# Patent

## Title
Method of producing L-serine derivative and enzyme used therefore

## Abstract

The present invention provides a new method for producing serine derivatives and their optically-activated derivatives in a convenient manner. In the presence of an enzyme, an L-α-amino acid of formula (I):




(in the formula (I), R1 is a hydrocarbon group)

is reacted with an aldehyde of formula (II):





(in the formula (II), R2 is a hydrocarbon)

to produce an L-serine derivative of formula (III).





.

## Background
This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2005-148660, filed May 20, 2005, and is a continuation under 35 U.S.C. §120 of PCT Patent Application No. PCT/JP2006/309949, filed May 18, 2006, both of which are incorporated by reference. The Sequence Listing filed electronically herewith is also hereby incorporated by reference in its entirety (File Name: US-352_Seq_List_Copy—1; File Size: 64 KB; Date Created: Nov. 20, 2007).


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing β-hydroxy-α-L-amino acid and in particular, to a method for producing an L-serine derivative with a novel enzyme.
2. Brief Description of the Related Art
Derivatives of the amino acid serine and amino acids having optical activity in the a position are typically used as intermediates in the production of pharmaceuticals. Examples of methods for producing optically active α-alkyl serine derivatives, which have two different substituents in the α position, and salts thereof, include the following methods:
1) asymmetric alkylation of an optically active oxazolidine compound obtained from the optically active serine derivative and pivalaldehyde (Helvetica Chimica Acta, 1987, 70, 1194-1216);
2) asymmetric aldol reaction of α-isocyano carboxylic acid ester and paraformaldehyde with an optically active metal catalyst (Tetrahedron Letters, 1988, 29, 235-238);
3) asymmetric alkylation of optically active β-lactam compounds obtained from an optically active oxazolidine chromium carbene complex and an oxazine compound (Journal of Organic Chemistry, 1993, 58, 5918-5924);
4) asymmetric ring-opening reaction of an optically active aziridine compound (Tetrahedron Letters, 1995, 36, 3639-3642)
5) asymmetric alkylation of an optically active pyrazinone compound obtained from an optically active valine derivative and an optically active alanine derivative (European Journal of Organic Chemistry, 2000, 2809-2820); and
6) Sharpless asymmetric dihydroxylation of a 2-methyl-2-propenoic acid derivative followed by introduction of the resulting optically active diol compound into an optically active azido compound for reduction (Tetrahedron Asymmetry, 2001, 12, 949-957).
α-Methyl-L-serine is a promising substance which may be used as an intermediate in the production of a medicament. In one of the known methods for producing α-methyl-L-serine by means of an enzymatic reaction, D-alanine and 5,10-methylenetetrahydrofolic acid are used as the materials, and 2-methyl serine hydroxymethyl transferase (EC 2.1.2.7) is used as the enzyme (Wilson et al., J. Biol. Chem. 237 3171-3179).
SUMMARY OF THE INVENTION
As mentioned above, many studies have been conducted on a wide variety of methods for producing optically active amino acids. However, there are many kinds of optically active amino acids and serine derivatives. A simpler method or an effective and low-cost method for producing optically active amino acids and serine derivatives is desired. An aspect of the present invention is to provide a novel simpler method for producing the serine derivatives and optically active substance thereof, as well as enzymes useful in such methods.
The inventors of the present invention have developed a novel method for producing serine derivatives, and have discovered a new protein. This protein catalyzes the reaction of an L-amino acid and a predetermined aldehyde. In addition, the inventors discovered that this protein could be used to conveniently produce serine derivatives, and also selectively produce an L-serine derivative having optical activity. Therefore, a reaction system in which the amino acid and formaldehyde were directly reacted in the absence of 5,10-methylenetetrahydro folic acid, was established. This type of reaction system has not been found before. The present invention is based on the knowledge of these discoveries by the inventors. The present invention provides a method for producing an L-serine derivative and enzymes used in the method, as mentioned below.
It is an aspect of the present invention to provide a method for producing a L-serine derivative of formula (III):




comprising:
reacting L-α-amino acid of formula (I):




with aldehyde of formula (II):




in the presence of an enzyme,
wherein R1 is selected from the group consisting of an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent, and
wherein R2 is selected from a group of a hydrogen, an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent.
It is a further aspect of the present invention to provide the method for producing the L-serine derivative as described above, wherein said enzyme is derived from a microorganism belonging to a genus selected from the group consisting of Ralstonia, Variovorax, Bosea and Silicibacter. 
It is a further aspect of the present invention to provide the method for producing the L-serine derivative as described above, wherein said enzyme is a protein selected from a group consisting of:
(A) a protein comprising the amino acid sequence of SEQ ID No: 5;
(B) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 5, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(C) a protein comprising the amino acid sequence of SEQ ID NO: 9;
(D) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 9, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(E) a protein comprising an amino acid sequence of SEQ ID NO: 15;
(F) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 15, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(G) a protein comprising the amino acid sequence of SEQ ID NO: 19;
(H) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 19, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(I) a protein comprising the amino acid sequence of SEQ ID NO: 23;
(J) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 23, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(K) a protein comprising the amino acid sequence of SEQ ID NO: 30; and
(L) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 30, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III).
It is a further aspect of the present invention to provide the method for producing the L-serine derivative as described above, wherein said L-α-amino acid is L-α-alanine and said L-serine derivative is α-methyl-L-serine.
It is a further aspect of the present invention to provide the method for producing the L-serine derivative as described above, wherein said L-α-amino acid is L-2-amino-n-butyric acid and said L-serine derivative is α-ethyl-L-serine.
It is a further aspect of the present invention to provide the method for producing the L-serine derivative as described above, wherein said L-α-amino acid is L-α-alanine and said L-serine derivative is α-methyl-L-threonine.
It is a further aspect of the present invention to provide a protein derived from a microorganism belonging to a genus selected from the group consisting of Ralstonia, Variovorax, Bosea, and Silicibacter, 
wherein said protein is able to catalyze a reaction of an L-α-amino acid of formula (I):




with an aldehyde of formula (II)




to produce a L-serine derivative of formula (III):




wherein R1 is selected from the group of an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent, and
wherein R2 is selected from a group of a hydrogen, an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent.
It is a further aspect of the present invention to provide a protein which is able to catalyze a reaction of an L-α-amino acid of formula (I):




with an aldehyde of formula (II)




to produce a L-serine derivative of formula (III):




wherein R1 is selected from the group consisting of an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent, and
wherein R2 is selected from the group consisting of a hydrogen, an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent, and
wherein said protein is selected from the group consisting of:
(A) a protein comprising the amino acid sequence of SEQ ID No: 5;
(B) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 5, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(C) a protein comprising the amino acid sequence of SEQ ID NO: 9;
(D) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 9, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(E) a protein comprising an amino acid sequence of SEQ ID NO: 15;
(F) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 15, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(G) a protein comprising the amino acid sequence of SEQ ID NO: 19;
(H) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 19, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(I) a protein comprising the amino acid sequence of SEQ ID NO: 23;
(J) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 23, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(K) a protein comprising the amino acid sequence of SEQ ID NO: 30; and
(L) a protein comprising an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 30, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition and inversion, and wherein said protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III).
It is a further aspect of the present invention to provide a polynucleotide encoding a protein as described above.
It is a further aspect of the present invention to provide a polynucleotide selected from the group consisting of:
(a) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 4;
(b) a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 4 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
(c) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 8;
(d) a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 8 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
(e) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 14;
(f) a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 14 under stringent conditions, and which encodes a protein having an activity of catalyzing a reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
(g) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 18;
(h) a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 18 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
(i) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 22;
(j) a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 22 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
(k) a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 29; and
(l) a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 29 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III); and
wherein formula (I) is:




wherein R1 of formula (I) is selected from the group consisting of an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent;
wherein said formula (II) is:




wherein R2 of formula (II) is selected from the group consisting of a hydrogen, an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and these groups may be either linear or branched and may have a substituent;
wherein said formula (III) is:




It is a further aspect of the present invention to provide a recombinant polynucleotide comprising said polynucleotide as described above.
It is a further aspect of the present invention to provide a transformant having said polynucleotide as described above.
The present invention allows L-serine derivatives to be produced by a simple method. Moreover, the present invention allows L-amino acids, such as the L-serine derivative having an optical activity, to be selectively produced, which provides an effective method for producing these types of L-amino acids.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a scheme showing the reaction system.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments according to the present invention are described with reference to the best mode of carrying out the invention.
Various types of genetic engineering approaches and methods are described in many standard experimental manuals, such as Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor press (2001/01/15), Saibo Kogaku Handbook (Cellular Engineering Handbook), Toshio KUOKI et al., Yodosya (1992), and Shin Idenshi Kogaku Handbook (New Gene Engineering Handbook), 3rd edition, Matsumura et al., Yodosya (1999), and by reference to these, any person skilled in the art may easily use these methods. An enzyme is a protein which is able to catalyze a chemical reaction.
To produce an L-serine derivative, an L-α-amino acid of formula (I) is reacted with an aldehyde of formula (II).
The alkyl group of R1 with 1 to 6 carbons includes, but is not limited to, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, a neo-pentyl group, a n-hexyl group, and an isohexyl group.
The aryl group of R1 with 6 to 14 carbons includes, but is not limited to, a phenyl group, a tolyl group, a xylyl group, a biphenylyl group, a naphthyl group, an antolyl group, and a phenantolyl group.
The cycloalkyl group of R1 with 3 to 10 carbons includes, but is not limited to, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptenyl group, a cyclooctanyl group, a cyclononenyl group, and a cyclodecenyl group.
The aralkyl group of R1 with 7 to 19 carbons includes, but is not limited to, phenylalkyl groups such as a benzyl group, a benzhydryl group, a phenethyl group, and a trityl group, a cinnamyl group, a stylyl group, and a naphthylalkyl group.
The alkoxyalkyl group of R1 with 2 to 11 carbons includes, but is not limited to an alkyl group with 1 to 10 carbons which has a substituent selected from the group consisting of a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a pentyloxy group, a phenoxy group, a heptoxy group, an octoxy group, a nonanoxy group, a decanoxy group, and an undecoxy group.
R1 may also be a group which has a carbon skeleton containing a hetero atom in any of the aforementioned hydrocarbons. Examples of the hetero atom include, but are not limited to, an oxygen atom, a nitrogen atom, and a sulfur atom.
When R1 is a hydrocarbon group containing a hetero atom in its carbon skeleton, it may include a heterocycle-containing hydrocarbon group. The heterocycle-containing hydrocarbon group is a cyclic hydrocarbon group, wherein the cyclic moiety contains the hetero atom. Examples of the heterocyclic hydrocarbon group include, but are not limited to, a heteroaryl group with or without aromaticity and may be either a monocyclic or polycyclic group. Specific examples of the heterocyclic hydrocarbon group include, but are not limited to, a furilic group, a thienyl group, a pyridyl group, a piperidyl group, a piperidino group, a morpholino group, an indolyl group, an imidazolyl group, and an alkyl group substituted with any of these heterocyclic groups.
In addition, R1 may also be a hydrocarbon group which has a carbon skeleton containing a unsaturated carbon-carbon bond in any of the aforementioned groups.
In addition, the aforementioned R1 may be linear or branched. Moreover, R1 may be the aforementioned hydrocarbon group which is partially substituted with the following group or to which the following group is partially added: one or more groups which may include a halogen atom, an alkyl group with up to 3 carbons, an alkoxyl group with up to 3 carbons, a keto group (═O), a hydroxyl group (—OH), a thiol group (—SH), an amino group (—NH2), an amido group (—CONH2), an imino group (═NH), and a hydrazino group (—NHNH2).
Examples of the L-α-amino acid of formula (I) include, but are not limited to, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, asparagine, glutamine, phenylalanine, tyrosine, tryptophan, aspartic acid, glutamic acid, lysine, arginine, histidine, and 2-amino-n-butyric acid. All of these are of the L-α-type, preferably, alanine and 2-amino-n-butyric acid, and more preferably, alanine.
R2 of formula (II) may be specifically described as follows.
R2 may be hydrogen.
The alkyl group of R2 with 1 to 6 carbons includes, but is not limited to, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, a neo-pentyl group, n-hexyl group, and an isohexyl group.
The aryl group of R2 with 6 to 14 carbons includes, but is not limited to, a phenyl group, a tolyl group, a xylyl group, a biphenylyl group, a naphthyl group, an antolyl group, and a phenantolyl group.
When R2 is a cycloalkyl group with 3 to 10 carbons, specific examples include, but are not limited to, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptenyl group, a cyclooctanyl group, a cyclononenyl group, and a cyclodecenyl group.
The aralkyl group of R2 with 7 to 19 carbons includes, but is not limited to, phenylalkyl groups such as a benzyl group, a benzhydryl group, a phenethyl group, and a trityl group, a cinnamyl group, a stylyl group, and a naphthylalkyl group.
The alkoxyalkyl group of R2 with 2 to 11 carbons includes, but is not limited to an alkyl group with 1 to 10 carbons which has a substituent of a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a pentyloxy group, a phenoxy group, a heptoxy group, an octoxy group, a nonanoxy group, a decanoxy group, or an undecoxy group.
R2 may also be a group which has a carbon skeleton containing a hetero atom in any of aforementioned hydrocarbon groups. The examples of the hetero atom include, but are not limited to, an oxygen atom, a nitrogen atom, and a sulfur atom.
When R2 is a hydrocarbon group containing a hetero atom in its carbon skeleton, it may include a heterocycle-containing hydrocarbon group. The heterocycle-containing hydrocarbon group is a cyclic hydrocarbon group, wherein a cyclic moiety contains the hetero atom. Examples of the heterocycle-containing hydrocarbon group includes, but is not limited to, a heteroaryl group with or without aromaticity and may be either monocyclic or polycyclic group. Specific examples of the heterocyclic hydrocarbon group include, but are not limited to, a furilic group, a thienyl group, a pyridyl group, a piperidyl group, a piperidino group, a morpholino group, an indolyl group, an imidazolyl group, and an alkyl group substituted by any of these heterocyclic groups.
In addition, R2 may also be a hydrocarbon group which has a carbon skeleton containing an unsaturated carbon-carbon bond in any of the aforementioned groups.
In addition, the aforementioned R2 may be linear or branched. Moreover, R2 may be the aforementioned hydrocarbon group which is partially substituted with the following group or to which the following group is partially added: one or more groups selected from a group of a halogen atom, an alkyl group with up to 3 carbons, an alkoxyl group with up to 3 carbons, a keto group (═O), a hydroxyl group (—OH), a thiol group (—SH), an amino group (—NH2), an amido group (—CONH2), an imino group (═NH), a hydrazino group (—NHNH2).
Examples of compounds of formula (II) may preferably include formaldehyde and acetaldehyde.
R1 and R2 of formula (III) are the same as R1 and R2 of formula (I) and (II), respectively. According to a specific combination of R1 and R2, the product may be an optically-inactive stereoisomer (mesoisomer). The method of the present invention is a method for producing an amino acid having an optical activity; therefore, the present invention does not include a combination of R1 and R2 which result in the production of the mesoisomer. For example, α-hydroxymethyl-serine is not an L-serine derivative; therefore, the combination of serine as a compound of formula (I) and formaldehyde as a compound of formula (II) is not included in the method for producing the L-serine derivative of the present invention.
The method of the present invention for producing the L-serine derivative involves a process of preferentially producing the L-serine derivative by the reaction with an enzyme. Herein, the phrase “preferentially producing the L-serine derivative” means that the ratio of the L-serine derivative is higher than the ratio of a D-serine derivative among the serine derivatives to be produced, and the ratio is preferably 70% or more, more preferably 80% or more, and further preferably 90% or more. In this case, the ratio of the L-serine derivative among the L-serine derivatives is calculated by the formula:

[L-serine derivative]/([D-serine derivative]+[L-serine derivative])*100.

One preferred embodiment of the method of the present invention includes a reaction system, in which α-methyl-L-serine is produced through the reaction of L-α-alanine and formaldehyde. FIG. 1 shows a specific example of the reaction system. The reaction system, in which formaldehyde is reacted directly with the L-amino acid without involving a compound such as 5,10-methylentetrahydro folic acid to produce the L-serine derivative, has not been known at all. According to the method of the present invention, the L-serine derivative may be produced in a simpler reaction system. In the case of using formaldehyde, it is preferable that a small amount of formaldehyde is added sequentially in the reaction system. The sequential addition of formaldehyde may suppress the generation of byproducts.
Another preferable embodiment of the present invention may include reaction systems in which α-ethyl-L-serine is produced through the reaction of L-2-amino-n-butyric acid and formaldehyde; and α-methyl-L-threonine is produced through the reaction of L-α-alanine and acetaldehyde.
A reaction temperature is preferably 10 to 60° C. and more preferably 20 to 40° C. The pH value for the reaction system is preferably 4 to 10 and more preferably 6 to 8.
An example of the method of isolating an L-serine derivative from the resulting solution of the aforementioned enzymatic reaction is as follows. Dissolved proteins are flocculated by lowering the pH with thermal sterilization, and then microbes and proteins are removed from the solution by means such as centrifugation, filtration, and ultra filtration (UF). Because the resulting solution includes inorganic salts, the solution is desalted to avoid precipitation of those salts during crystallization. Applicable methods may include any method such as nanofiltration (NF), electrodialysis, and ion exchange using a resin.
After the aforementioned desalting, when necessary, the solution is concentrated. Then, the L-serine derivative begins to crystallize; however, due to the crystals' fine and highly solvable properties, it is often difficult to isolate. Furthermore, the ratio of the recovered crystals cannot be allowed to be high, and the high viscosity makes handling difficult.
Therefore, crystallization by adding a poor solvent is preferably conducted after the solution is preliminarily concentrated to some extent, when necessary. For example, the preliminary concentrating may be continued until crystals begin to precipitate. Preferable examples of the poor solvent include lower alcohols and acetone, which are water soluble. Continuing with cooling crystallization after the crystallization with the poor solvent may also help to improve the crystallization ratio. The resulting slurry is isolated and the wetting cake thereof is dried to obtain crystals of the L-serine derivative.
According to the method of the present invention, an aldehyde of formula (II) is reacted with the L-α-amino acid in the presence of a predetermined enzyme. The enzyme capable of catalyzing the reaction may be obtained from a microorganism belonging to a genus such as Ralstonia, Variovorax, Bosea, and Silicibacter. More specific examples of the microorganism may include Ralstonia sp., Variovorax paradoxus, Bosea sp. and Silicibacter pomeroyi; preferably, Ralstonia sp. FERM ABP-10607, Variovorax paradoxus FERM ABP-10608, Variovorax paradoxus NBRC 15149, Variovorax paradoxus NBRC 15150, Bosea sp. FERM ABP-10609 and Silicibacter pomeroyi DSM 15171.
Strains having a FERM or NBRC number assigned are deposited strains as mentioned below; therefore, they are available by referencing the associated number and following the given procedure.
(1) Nomenclature: Ralstonia sp. A11 (or, AJ110405)
Deposit Number: FERM ABP-10607
Depositary authority: International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology
Address: Chuoh No. 6, Higashi 1-1-1, Tsukuba, Ibaraki, Japan
Deposit date: Mar. 8, 2005
(2) Nomenclature: Variovorax paradoxus B2-B2 (or, AJ110406 strain)
Deposit Number: FERM ABP-10608
Depositary authority: International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology
Address: Chuoh No. 6, Higashi 1-1-1, Tsukuba, Ibaraki, Japan
Deposit date: Mar. 8, 2005
(3) Nomenclature: Variovorax paradoxus AJ110408
Deposit Number: NBRC15149
Depositary authority: NITE Biological Resource Center
Department of Biotechnology (NBRC), Department of Biotechnology (DOB), National Institute of Technology and Evaluation (NITE)
Address: Kazusa Kamatari 2-5-8, Kisarazu, Chiba, Japan
(4) Nomenclature: Variovorax paradoxus AJ110409
Deposit Number: NBRC15150
Depositary authority: NITE Biological Resource Center
Department of Biotechnology (NBRC), Department of Biotechnology (DOB), National Institute of Technology and Evaluation (NITE)
Address: Kazusa Kamatari 2-5-8, Kisarazu, Chiba, Japan
(5) Nomenclature: Bosea sp. B2-R1 (or, AJ110407)
Deposit Number: FERM ABP-10609
Depositary authority: International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology
Address: Chuoh No. 6, Higashi 1-1-1, Tsukuba, Ibaraki, Japan
Deposit date: Mar. 8, 2005
Other than those strains, Silicibacter pomeroyi DSM 15171 is accessible to the public at Deusche Sammulung von Mikroorganismen und Zellkulturen GmbH (Address: Mascheroder Weg 1b, 38124 Braunschweig, GERMANY), and at the American Type Culture Collection (Contact: P.O. Box 1549, Manassas, Va. 20108, U.S.A.), with the reference number ATCC700808.
Tables 1-1 and 1-2 describe the mycological characteristics of Ralstonia sp. All strain (or, AJ110405, Deposit NO: FERM ABP-10607).







TABLE 1-1





Ralstonia sp. A11







1. Morphological characteristics








Culture conditions
Nutrient agar (Oxoid,



Hampshire, England)



culture medium, 30° C.


Cell morphology
Short bacillus (0.6 × 0.8 μm)


Cell polymorphism
−


Motility (flagellar immobility)
−


Spore (sporal site)
−







2. Culture characteristics








Culture conditions
Nutrient agar (Oxoid,



Hampshire, England)



culture medium, 30° C.


Color
Pale yellow


Luster
+


Color development
−


Culture conditions
Nutrient broth (Oxoid,



Hampshire, England)



culture medium, 30° C.


Surface growth
−


Cloudiness of culture medium
+


Culture condition
Gelatin stick culture 30° C.


Growth condition
+


Gelatin liquification1)
−


Culture condition2)
Litmus milk 30° C.


Coagulation
−


Liquification
−







3. Physiological characteristics








Gram stainability1)
−


Nitrate reduction3)
−


denitrification3)
+


MR test2)
−


VP test3)
−


Indole production3)
−


Production of hydrogen sulfide3)
−


Starch hydrolysis2)
−









Use of citric
(Koser)
+


acid2)
(Christensen)
+


Use of inorganic
Nitrate
+


nitrogen
Ammonium salt
+


resource2)


Urease activity3)

−


Catalase2)

+


Oxidase2)

+


Growth range;
 6
+


pH
 8
+



 9
+w


Growth range;
25
+


temperature (° C.)
30
+



37
+w



45
−








Anaerobic growth
−


O—F test (acidic/fermented)2)
−/−
















TABLE 1-2







4. Acid production/gas generation from saccharide2)












L-arabinose
−/−
D-xylose
−/−



D-glucose
−/−
D-mannose
−/−



D-fractose
−/−
D-galactose
−/−



maltose
−/−
sucrose
−/−



lactose
−/−
Trehalose
−/−



D-sorbitol
−/−
D-mannitol
−/−



inositol
−/−
Glycerin
−/−







5. Other physiological characteristics2)










β-galactosidase activity
−



arginine dihydrolase activity
−



lysine decarboxylase activity
−



tryptophan deaminase activity
−



Gelatinase activity
−







+: positive,



−: negative,



w: weakly reacted






Tables 2-1 and 2-2 describe the mycological characteristics of Variovorax paradoxus B2-B2 (AJ110406 strain, Deposit NO: FERM ABP-10608).







TABLE 2-1





Variovorax paradoxus B2-B2







1. Morphological characteristics








Culture conditions
Nutrient agar (Oxoid, Hampshire,



England)



culture medium, 30° C.


Cell morphology
(0.6-07 × 1.5-2.0 μm)


Cell polymorphism
−


Motility (flagellar immobility)
+


Spore (sporal site)
−







2. Culture characteristics








Culture conditions
Nutrient agar (Oxoid, Hampshire,



England)



culture medium, 30° C.


Color
Yellow


Luster
+


Color development
+


Culture condition
Nutrient broth (Oxoid, Hampshire,



England)



culture medium, 30° C.


Surface growth
−


Cloudiness of culture medium
+


Culture conditions
Gelatin stick culture 30° C.


Growth conditions
−


Gelatin liquification1)
−


Culture conditions2)
Litmus milk 30° C.


Coagulation
−


Liquification
−







3. Physiological characteristics








Gram stainability1)
−


Nitrate reduction3)
−


denitrification3)
+


MR test2)
−


VP test3)
−


Indole production3)
−


Production of hydrogen sulfide3)
−


Starch hydrolysis2)
−









Use of citric
(Koser)
−


acid2)
(Christensen)
+


Use of inorganic
Nitrate
+w


nitrogen
Ammonium salt
+w


resource2)


Urease activity3)

−


Catalase2)

+


Oxidase2)

−


Growth range;
 6
+


pH
 8
+



 9
+


Growth range;
25
+


temperature (° C.)
30
+



37
+w



45
−








Anaerobic growth
+


O—F test (acidic/fermented)2)
−/−
















TABLE 2-2







4. Acid production/gas generation from saccharide2)












L-arabinose
−/−
D-xylose
−/−



D-glucose
−/−
D-mannose
−/−



D-fractose
−/−
D-galactose
−/−



maltose
−/−
sucrose
−/−



lactose
−/−
Trehalose
−/−



D-sorbitol
−/−
D-mannitol
−/−



inositol
−/−
Glycerin
−/−







5. Other physiological characteristics2)










β-galactosidase activity
−



arginine dihydrolase activity
−



lysine decarboxylase activity
−



tryptophan deaminase activity
−



Gelatinase activity
−







+: positive,



−: negative,



w: weakly reacted






Tables 3-1 and 3-2 describe the mycological characteristics of Bosea sp. B2-R1 strain (AJ110407, Deposit NO: FERM ABP-10609).







TABLE 3-1





Bosea sp. B2-R1







1. Morphological characteristics








Culture conditions
Nutrient agar (Oxoid, Hampshire,



England)



culture medium, 30° C.


Cell morphology
(0.6-07 × 1.5-2.0 μm)


Cell polymorphism
−


Motility (flagellar immobility)
+


Spore (sporal site)
−







2. Culture characteristics








Culture conditions
Nutrient agar (Oxoid, Hampshire,



England)



culture medium, 30° C.


Color
Pale yellow


Luster
+


Color development
−


Culture conditions
Nutrient agar (Oxoid, Hampshire,



England)



culture medium, 30° C.


Surface growth
−


Cloudiness of culture medium
+


Culture conditions
Gelatin stick culture 30° C.


Growth conditions
−


Gelatin liquification1)
−


Culture conditions2)
Litmus milk 30° C.


Coagulation
−


Liquification
−







3. Physiological characteristics








Gram stainability1)
−


Nitrate reduction3)
−


denitrification3)
−


MR test2)
−


VP test3)
−


Indole production3)
−


Production of hydrogen sulfide3)
−


Starch hydrolysis2)
−









Use of citric
(Koser)
+


acid2)
(Christensen)
+


Use of inorganic
Nitrate
+


nitrogen
Ammonium salt
+w


resource2)


Urease activity3)

−


Catalase2)

+


Oxidase2)

+


Growth range;
 6
+


pH
 8
+



 9
+


Growth range;
25
+


temperature (° C.)
30
+



37
+



45
−








Anaerobic growth
+


O—F test (acidic/fermented)2)
−/−
















TABLE 3-2







4. Acid production/gas generation from saccharide2)












L-arabinose
−/−
D-xylose
−/−



D-glucose
−/−
D-mannose
−/−



D-fractose
−/−
D-galactose
−/−



maltose
−/−
sucrose
−/−



lactose
−/−
Trehalose
−/−



D-sorbitol
−/−
D-mannitol
−/−



inositol
−/−
Glycerin
−/−







5. Other physiological characteristics2)










β-galactosidase activity
−



arginine dihydrolase activity
−



lysine decarboxylase activity
−



tryptophan deaminase activity
−



Gelatinase activity
−







+: positive,



−: negative,



w: weakly reacted






References and Kits Used:
1) BARROW, (G. I.) and FELTHAM, (R. K. A): Cowan and Steel's Manual for the Identification of Medical Bacteria. 3rd edition. 1993, Cambridge University Press.
2) Toshikazu SAKAZAKI, Etsuro YOSHIZAKI, and Kanji MIKI: Shin Saikin-baichi-gaku Kouza PART II (The Course of Culturing Medium for Microorganism PART II) <2nd edition>, 1988, Kindai Shuppan, Tokyo.
3) Bacteriopexy kit: AP120, NE.
(bioMerieux, France:http://www.biomerieux.fr/home_en.htm).
More specifically, examples of the enzymes used in the reaction for producing the L-serine derivative includes the following proteins:
(A) a protein of the amino acid sequence of SEQ ID No: 5;
(B) a protein of an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 5, wherein said variation is a substitution, deletion, insertion, addition and inversion, and wherein the protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(C) a protein of the amino acid sequence of SEQ ID NO: 9;
(D) a protein of an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 9, wherein said variation is a substitution, deletion, insertion, addition and inversion, and wherein the protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(E) a protein of an amino acid sequence of SEQ ID NO: 15;
(F) a protein of an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 15, wherein said variation is a substitution, deletion, insertion, addition and inversion, and wherein the protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(G) a protein of the amino acid sequence of SEQ ID NO: 19;
(H) a protein of an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 19, wherein said variation is a substitution, deletion, insertion, addition and inversion, and wherein the protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(I) a protein of the amino acid sequence of SEQ ID NO: 23;
(J) a protein of an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 23, wherein said variation a substitution, deletion, insertion, addition and inversion, and wherein the protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III);
(K) a protein of the amino acid sequence of SEQ ID NO: 30; and
(L) a protein of an amino acid sequence which has variation of one or a small number of amino acid(s) in the amino acid sequence of SEQ ID NO: 30, wherein said variation is a substitution, deletion, insertion, addition and inversion, and wherein the protein has an activity of catalyzing the reaction to form said L-serine derivative of formula (III).
Any of the aforementioned proteins may be used to conveniently produce the L-serine derivative. In particular, when L-α-alanine reacts with formaldehyde, only α-methyl-L-serine is substantially produced. The optically active amino acid is therefore efficiently obtained.
The protein having the amino acid sequence of SEQ ID NO: 5 may be isolated from Ralstonia sp. FERM ABP-10607. The protein having the amino acid sequence of SEQ ID NO: 9 may be isolated from Variovorax paradoxus FERM ABP-10608. The protein having the amino acid sequence of SEQ ID NO: 15 may be isolated from Variovorax paradoxus NBRC15149. The protein having the amino acid sequence of SEQ ID NO: 19 may be isolated from Variovorax paradoxus NBRC15150. The protein having the amino acid sequence of SEQ ID NO: 23 may be isolated from Bosea sp. FERM ABP-10609. The protein having the amino acid sequence of SEQ ID NO: 30 may be isolated from Silicibacter pomeroyi DSM 15171.
The genome sequence of Silicibacter pomeroyi DSM 15171 has been disclosed and a part of the sequence of SEQ ID NO: 30 is registered as a serine hydroxymethyltransferase (AAV96754.1). As a result, serine hydroxymethyltransferase (AAV96754.1) which has the registered sequence was expressed in Eshcerichia coli, and the desired protein was not detected and the resulting products did not have any serine hydroxymethyltransferase activity. However, as a result of research by the inventors, it was discovered that nine amino acid residues upstream of the registered sequence is necessary for activity of 2-methylserine hydroxymethyltransferase. Therefore, the nine amino acid residues is added upstream of the registered sequence, resulting in the sequence of SEQ ID NO: 30. As a result of expressing the sequence of SEQ ID NO: 30 in Eshcerichia coli, it was confirmed that the desired protein was detected, which has 2-methylserine hydroxymethyltransferase activity.
As mentioned above, variant proteins which are substantially the same as the above-mentioned proteins may be used. First, taking the protein of SEQ ID NO: 5 as an example, a protein which is substantially the same as the protein of SEQ ID NO: 5 is also provided. Herein, the term “a small number” indicates a number of amino acids which result in a protein structure which retains substantially the same activity, specifically 1 to 50, preferably 1 to 30, and more preferably 1 to 10, depending on the position of the amino acid residue in the protein structure and the type of amino acid. The amino acid sequence of the variant protein, which has variation of one or a small number of amino acid(s), in which the variation is a substitution, deletion, insertion, addition, and inversion, preferably conserves approximately half or more of the oxygen activity, preferably 80% or more, more preferably 90% or more, and further preferably 95% compared with the protein (A) under the conditions of 30° C., pH 7 to 8.
The variation in amino acids as described in the aforementioned variant protein may be achieved by alternating the nucleotide sequence so that the amino acid which corresponds to the specific site of the gene encoding the protein is substituted, deleted, inserted, or added using, e.g., the site-specific mutagenic method. Alternatively, the polynucleotide having the nucleotide sequence altered as mentioned above may be obtained through known conventional mutation process. The mutation process includes in vitro treatment of the DNA encoding the protein of SEQ ID NO. 5, for example, with hydroxylamine or the like and a method in which the microorganism belonging to genus Escherichia, which carries DNA encoding the protein of SEQ ID NO. 5 is treated with UV irradiation or with a mutagenic agent which is commonly used for artificial mutation such as N-methyl-N′-nitro-N-nitrosoguanidine (NTG) and nitrous acid.
The aforementioned variation, such as substitution, deletion, addition, and inversion, also includes naturally-occurring variation such as differences in species and strain of the microorganism. By expressing the DNA having the variation mentioned above in appropriate cells to examine the enzyme activity of the expressed products, the DNA encoding the variant protein may be obtained.
Similar to the relationship between the protein of SEQ ID NO. 5 and its variant protein, each of the proteins of SEQ ID NOs. 9, 15, 19, 23, and 30 may also exist as variant proteins which are substantially the same as defined above for the protein of SEQ ID NO. 5 and its variant.
Examples of the variant proteins which are substantially the same as the proteins of SEQ ID NOs. 9, 15, 19, 23, and 30 include proteins which have an amino acid sequence with homology of preferably 70% or more, more preferably 80% or more, and further preferably 90% or more, with respect to each of the proteins. In the present specification, the homology of the amino acid sequence was obtained by calculating a Marching count which indicates the percentage over the full-length of the ORF of the encoded polypeptide, using GENETYX software Ver7.0.9 (Genetics) with Unit Size to Compare=2, or by an equivalent calculation method.
The present invention provides polynucleotides encoding the aforementioned proteins. Due to codon degeneration, an amino acid sequence may be defined by more than one nucleotide sequence. That is, the polynucleotide of the present invention includes a polynucleotide having the nucleotide sequences encoding the aforementioned proteins of SEQ ID NOs. 9, 15, 19, 23, and 30, and their variants.
Specifically, examples of the polynucleotides of the present invention include, but are not limited to, the following polynucleotides:
(a) a polynucleotide of a nucleotide sequence of SEQ ID NO: 4;
(c) a polynucleotide of a nucleotide sequence of SEQ ID NO: 8;
(e) a polynucleotide of a nucleotide sequence of SEQ ID NO: 14;
(g) a polynucleotide of a nucleotide sequence of SEQ ID NO: 18;
(i) a polynucleotide of a nucleotide sequence of SEQ ID NO: 22; and
(k) a polynucleotide of a nucleotide sequence of SEQ ID NO: 29.
The polynucleotide of SEQ ID NO. 4, encoding the protein of SEQ ID NO. 5, may be isolated from the Ralstonia sp. FERM ABP-10607. The polynucleotide of SEQ ID NO. 8, encoding the protein of SEQ ID NO. 9, may be isolated from the Variovorax paradoxus FERM ABP-10608. The polynucleotide of SEQ ID NO. 14, encoding the protein of SEQ ID NO. 15, may be isolated from the Variovorax paradoxus NBRC15149. The polynucleotide of SEQ ID NO. 18, encoding the protein of SEQ ID NO. 19, may be isolated from the Variovorax paradoxus NBRC15150. The polynucleotide of SEQ ID NO. 22, encoding the protein of SEQ ID NO. 23, may be isolated from the Bosea sp. FERM ABP-10609. The polynucleotide of SEQ ID NO. 29, encoding the protein of SEQ ID NO. 30, may be isolated from the Silicibacter pomeroyi DSM 15171.
Taking the polynucleotide of SEQ ID NO. 4 as an example, a method for isolating polynucleotides is described. The DNA having the nucleotide sequence listed in the sequence of SEQ ID NO. 4 may be obtained from a chromosomal DNA or a DNA library of Ralstonia sp. by PCR (polymerase chain reaction, refer to White, T. J. et al; Trends Genet., 5, 185 (1989)) or hybridization. A primer which can be used in PCR may be designed based on, for example, an internal amino acid sequence of the purified protein having an activity of catalyzing the reaction involved in the method of the present invention. Alternatively, the primer or a probe for hybridization may be designed based on the nucleotide sequence of SEQ ID NO: 4 or may be isolated using a probe. A combination of a primer having a sequence corresponding to a 5′ non-translated region, and a sequence corresponding to a 3′ non-translated region, between which is found the coding region, may be used for the primer for PCR. Then, PCR can be used to amplify the full-length of the protein coding region.
The primer may be synthesized in a typical manner, for example, by the phosphoramidite method (refer to Tetrahedron Letters (1981), 22, 1859) using DNA synthesizing equipment Model 380B (Applied Biosystems). The PCR process may be conducted using, for example, Gene Amp PCR System 9600 (PERKIN ELMER) and TaKaRa LA PCR in vitro Cloning Kit (TaKaRa Bio), according to the method specified by the suppliers or manufacturers.
Variant polynucleotides which are substantially the same as the aforementioned polynucleotides of SEQ ID NOs. 4, 8, 14, 18, 22, and 29 are also included in the present invention.
A variant polynucleotide of SEQ ID NO. 4 includes a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 4 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
A variant polynucleotide of SEQ ID NO. 8 includes a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 8 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
A variant polynucleotide of SEQ ID NO. 14 includes a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 14 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
A variant polynucleotide of SEQ ID NO. 18 includes a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 18 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid of formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III);
A variant polynucleotide of SEQ ID NO. 22 includes a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 18 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III); and
A variant polynucleotide of SEQ ID NO. 29 includes a polynucleotide which hybridizes with a polynucleotide having a nucleotide sequence complementary to that of SEQ ID NO: 29 under stringent conditions, and which encodes a protein having an activity of catalyzing the reaction of an L-α-amino acid formula (I) with an aldehyde of formula (II) to produce an L-serine derivative of formula (III).
A probe, for example, may be used to hybridize the polynucleotides as described above. In each case, the probe may be prepared in a typical manner based on the nucleotide sequences of SEQ ID Nos: 4, 8, 14, 18, 22, and 29. The objective polynucleotide may be isolated using the probe to hybridize in the usual manner. The DNA probe, for example, may be prepared by amplifying the nucleotide sequences cloned into a plasmid or a phage vector, cutting out the desired nucleotide sequence with a restriction enzyme, and then extracting the nucleotide sequence. The portion to be cut out may be adjusted according to the objective DNA. Once the aforementioned polynucleotide, which is substantially the same as any other nucleotide, has been detected, the polynucleotide may be amplified in a usual manner, such as PCR.
The “stringent conditions” indicate conditions under which a so-called specific hybrid is formed but a nonspecific hybrid is not formed. Although it is difficult to clearly define the condition in terms of numerical values, an example of such conditions may be those under which the DNAs having high homology, for example, 70% or more, more preferably 80% or more, further preferably 90% or more, and still further preferably 95% or more, are hybridized while the DNAs having lower homology are not hybridized. The homology (%) of the nucleotide sequences is represented by numeric values obtained by percentage calculation over the full-length of the ORF of each gene (including a stop codon) using GENETYX software Ver7.0.9 (Genetics) with Unit Size to Compare=6, pick up location=1. As another example, stringent conditions may be those of ordinary washing conditions in Southern hybridization, under which the DNAs are hybridized at 60° C. and salt concentration of 1×SSC, 0.1% SDS, and preferably 0.1×SSC, 0.1% SDS. The genes which hybridize under such conditions include, but are not limited to, a gene containing a stop codon or a gene encoding a non-active protein due to a mutation in the DNA sequence encoding the activity center region. However, these may be easily screened out by inserting the obtained genes in a commercially-available expression vector, expressing the genes in an appropriate host, and determining the enzyme activity of the expressed product by a method described herein.
As mentioned above, desirably, the aforementioned variant polynucleotide of SEQ ID NO. 4 conserves approximately half or more of catalytic activity, preferably 80% or more, and more preferably 90% or more compared with the protein having the amino acid sequence encoded by the nucleotide sequence of SEQ ID NO: 4 under the conditions of 30° C., pH 8.0. Likewise, the aforementioned relationship is applicable to the aforementioned variant polynucleotide of SEQ ID NO. 8 in connection with the protein of SEQ ID NO. 9; to the aforementioned variant polynucleotide of SEQ ID NO. 14 in connection with the protein of SEQ ID NO. 15; to the aforementioned variant polynucleotide of SEQ ID NO. 18 in connection with the protein of SEQ ID NO. 19; to the aforementioned variant polynucleotide of SEQ ID NO. 22 in connection with the protein of SEQ ID NO. 23; and to the aforementioned variant polynucleotide of SEQ ID NO. 29 in connection with the protein of SEQ ID NO. 30.
According to the method of the present invention, any form of the enzyme may be used as long as it is capable of catalyzing the aforementioned reaction in the reaction system. Examples of the specific forms thereof include a cultured product of an enzyme-producing microorganism, cells of the microorganism separated from the cultured product, and a processed cell product. The cultured product of the microorganism is a product obtained by culturing the microorganism. More specifically, the cultured product may include a product such as a mixture containing the cells of the microorganisms, the cultivation medium used for culturing the microorganism, and the substances produced by the cultured microorganism. The cells of the microorganisms may be washed before using. The processed cell product may be disrupted, lysed, and/or freeze-dried. Also, a crude-purified protein that is collected from the processed cells, and a purified protein that is further purified may also be used. As for the purified proteins, a partially-purified protein which is obtained by a variety of purification methods may be used. Alternatively, a protein which is fixed by a covalent bond method, an adsorption method, or an entrapment method may be used. Depending on the chosen microorganism, a the cells may be lysed during cultivation. In this case, the supernatant of the cultivation medium may also be used as the enzyme-containing substance.
Next, the method for producing the proteins of the present invention, and the method for preparing the recombinants and transformants used in producing the proteins will be described hereinbelow using the aforementioned protein of SEQ ID NO. 5 as an example. These methods of the present invention are also applicable to other proteins.
The transformant which expresses the aforementioned protein of SEQ ID NO. 5 may be prepared using a previously prepared recombinant polynucleotide which contains the polynucleotide having any of the aforementioned nucleotide sequences incorporated therein. The transformant which expresses the aforementioned protein of SEQ ID NO. 5 may be obtained by, for example, preparing a recombinant DNA containing a DNA having the nucleotide sequence of SEQ ID NO: 4, and then introducing the resulting DNA into an appropriate host. Examples of the host for expressing the protein include a variety of prokaryotic cells, including microorganisms belonging to genus Escherichia such as Escherichia coli, microorganisms belonging to genus Corynebacterium, Bacillus subtilis, and a variety of eukaryotic cells including Saccharomyces cerevisiae, Pichia stipitis, and Aspergillus oryzae. When a host is chosen which is easily handled without any expensive components for cultivation, L-serine derivatives may be easily produced on a large scale.
The recombinant DNA for introducing the DNA of SEQ ID NO. 4 into a host may be prepared by inserting the DNA into a vector suitable for the type of the host, so that the inserted DNA can express the protein encoded thereby. If the native promoter to the gene encoding the aforementioned enzyme derived from microorganisms such as Ralstonia sp., Variovorax paradoxus, and Bosea sp. is capable of functioning in the host cell, this promoter may be used to express the protein. Alternatively, if necessary, other promoters which function in the host may be linked to the DNA of SEQ ID NO: 4, for example, so that the proteins are expressed under the control of the promoter.
The method for introducing the recombinant DNA into the host cell includes the D. M. Morrison method (Methods in Enzymology 68, 326 (1979)) and a method for increasing the permeability of the DNA by treating the recipient host cells with calcium chloride (Mandel, M. and Higa, A., J. Mol. Biol., 53, 159 (1970)).
When the objective proteins are produced on a large-scale using recombinant DNA technology, the association of the proteins to form protein inclusion bodies within the host transformant, is also for a preferred method for carrying out the present invention. The advantages of this expression production method is the protection of the objective protein from digestion from proteases in the microbial cells, and easy purification of the objective protein by disruption of the microbial cells followed by centrifugation. To obtain the active protein from the protein inclusion body, a series of manipulations such as solubilization and activity regeneration is required, and thus, the manipulations are more complicated than those used when directly producing the active protein. However, when a protein which affects microbial cell growth is produced on a large scale in the microbial cells, the effects thereof may be avoided by accumulating the protein as an inactive inclusion body in the microbial cells.
Examples of the methods for producing the objective protein on a large scale as an inclusion body includes methods of expressing the objective protein alone under the control of a strong promoter, as well as methods of expressing the objective protein as a fusion protein with a protein known to be expressed in a large amount.
As the host to be transformed, any strain commonly used to express heterogenes may be used. Suitable examples thereof include the Escherichia coli JM109, DH5α, HB101, and BL21(DE3) strains, which are subspecies of the Escherichia coli K12 strain. The method for transforming the host and the method for selecting the transformants are described in Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor press (2001/01/15). An example of the method for preparing the transformed Escherichia coli and producing a predetermined enzyme using the transformed E. coli will be specifically described hereinbelow.
As the promoter for expressing the DNA encoding the protein having catalytic activity used for the present invention, the promoters typically used for producing xenogenic proteins in E. coli may be used, and examples thereof may include strong promoters such as T7 promoter, lac promoter, trp promoter, trc promoter, tac promoter, and PR promoter and PL promoter, T5 promoter of lambda phage. As the vector, pUC19, pUC18, pBR322, pHSG299, pHSG298, pHSG399, pHSG398, RSF1010, PACYC177, pACYC184, pMW119, pMW118, pMW219, pMW218, pQE30, and derivatives thereof may be used. Other vectors of phage DNA may also be used. In addition, expression vectors which contain a promoter and can express the inserted DNA sequence may also be used.
In order to produce the protein in the form of a fusion protein inclusion body, a fusion protein gene is prepared by linking a gene encoding the second protein, preferably a hydrophilic peptide, to the upstream or downstream of the aforementioned protein. Such a gene encoding another protein may be those which increase the amount of the accumulated fusion protein and enhance the solubility of the fusion protein after denaturation and regeneration. Examples of candidates thereof may include the T7 gene 10, β-galactosidase gene, dehydrofolic acid reductase gene, interferon γ gene, interleukin-2 gene and prochymosin gene.
Such a gene may be ligated to the gene encoding the protein so that reading frames of codons are matched. This may be achieved by ligating at an appropriate restriction enzyme site or using a synthetic DNA having an appropriate sequence.
In some cases, it is preferable to ligate a terminator, i.e. the transcription termination sequence, downstream of the fusion protein gene in order to increase the production amount. Examples of this terminator may include T7 terminator, fd phage terminator, T4 terminator, tetracycline resistant gene terminator, and E. coli trpA gene terminator.
The vector for introducing the gene encoding the protein having catalytic activity or the fusion protein thereof into E. coli is preferably a multicopy vector. Examples thereof include plasmids having a replication origin derived from ColE1, such as pUC based plasmids, pBR322 based plasmids or derivatives thereof. As used herein, the term “derivative” means the plasmid modified by the substitution, deletion, insertion, addition and/or inversion of bases. “Modified” referred to herein includes modification by mutagenesis with a mutagen or UV irradiation, and natural mutation.
In order to select the transformants, it is preferable to employ a vector having a marker such as an ampicillin resistant gene. As such a plasmid, expression vectors having a strong promoter are commercially available (pUC series: Takara Bio Co., Ltd., pPROK series and pKK233-2: Clontech, etc.).
The DNA fragment containing the promoter, the gene encoding the protein having the objective activity or the fusion protein of the objective protein with the other protein, and in some cases the terminator, are ligated sequentially, and then ligated to the vector DNA to obtain a recombinant DNA.
The resulting recombinant DNA is used to transform Escherichia coli, and then the transformed Escherichia coli is cultured, so to express and produce the predetermined protein or its fused protein.
In the case of expressing the fusion protein, the fusion protein may be cleaved to obtain the objective protein using a restriction protease which recognizes a sequence not present in the objective protein, such as blood coagulation factor Xa, kallikrein.
As production media, media such as M9-casamino acid medium and LB medium which are typically used for cultivation of E. coli may be used. The conditions for cultivation and a production induction may be appropriately selected depending on types of the marker and the promoter of the vector and the host used.
The following methods are available for recovering the objective protein or the fusion protein containing the objective protein. If the objective protein or the fusion protein thereof is solubilized in the microbial cells, the cells may be collected and then disrupted or lysed to thereby obtain a crude enzyme solution. If necessary, the crude solution may be purified using techniques such as ordinary precipitation, filtration and column chromatography, to obtain the purified objective protein or the fusion protein. In this case, the purification may be performed using an antibody against the objective protein or the fusion protein. When the protein inclusion body is formed, it may be solubilized with a denaturant, and then the denaturant may be removed by dialysis or the like to obtain the objective protein.
EXAMPLES
The present invention will be described in more detail with reference to the following non-limiting examples.
Example 1
Detection of 2-Methyl Serine Hydroxylmethyl Transferase Activity
In a Nutrient Broth agar medium (Difco), the microorganisms listed in Table 4 were cultured at 30° C. for 24 hours. A platinum loopful of the resulting cells were inoculated into 3 ml of Nutrient Broth liquid medium and then cultured at 30° C. for 24 hours, with 120 reciprocations/minute. 0.15 ml of the resulting culture was inoculated into 3 ml of Nutrient Broth liquid medium containing 0.2% α-methyl-DL-serine and cultured at 30° C. for 24 hours at 120 reciprocations/minute.
After cultivation, the cells were centrifuged and then washed twice with an equal volume of 50 mM potassium phosphate buffer (pH 7.4) containing 0.1 mM pyridoxal phosphate. 50 mM potassium phosphate buffer (pH 7.4) containing 0.1 mM pyridoxal phosphate was used to prepare a total amount (0.3 ml) of cell suspension, and then the suspension was ultrasonically disrupted at 4° C. The supernatant obtained by centrifugation (16,000 g, 10 min.) was dialyzed with 50 mM potassium phosphate buffer (pH 7.4) containing 0.1 mM pyridoxal phosphate to obtain a cell-free extracted solution.
0.05 ml of the cell-free extracted solution was added to a reaction mixture of 50 mM potassium phosphate buffer (pH 7.4), 10 mM α-methyl-DL-serine, 0.1 mM pyridoxal phosphate, and 1 mM magnesium sulfate, and then a total amount (0.1 ml) of mixture was reacted at 30° C. for 10 minutes. The reaction was stopped by mixing 0.1 ml of alkaline agent (5N-potassium hydroxide) supplied with the Formaldehyde Kit-Test Wako (Wako). Subsequently, the formaldehyde detection reaction was executed by reference to the manual supplied with the kit to measure absorbance at 550 nm (E11). As a control, another reaction was performed in the same way as above, except that α-methyl-DL-serine was replaced with water in the aforementioned solution, and the absorbance (E10) of the resulting mixture was measured.
The change in adsorption specific to α-methyl-DL-serine was calculated (EΔ1=E11−E10). The results are shown in Table 4. As the results shows, 2-methyl serine hydroxymethyl transferase activity was confirmed.










TABLE 4







Strain
EΔ1









Ralstonia sp. A11
0.70



Variovorax paradoxus B2-B2
0.86



Bosea sp. B2-R1
0.42










Example 2
Purification of 2-Methyl Serine Hydroxymethyl Transferase Derived from and Native to the Ralstonia sp. A11 (AJ110405) Strain
(1) Preparation of the Cell-Free Extracted Solution
Cells of Ralstonia species were cultured in the Nutrient Broth agar medium (Difco) at 30° C. for 25.5 hours. The cultured cells were inoculated into 50 ml of Nutrient Broth liquid medium in a 500 ml Sakaguchi flask, and cultured at 30° C. for 21 hours, 120 reciprocation/minute. The resulting culture was inoculated into 2 L of liquid medium containing 0.2% α-methyl-DL-serine, 0.17% Yeast Nitrogen Base w/o amino acid and ammonium sulfate (pH 7.0). 100 ml each of the mixture was dispensed into 500 ml Sakaguchi flasks, and then cultured at 30° C. for 24 hours, 120 reciprocation/minute. The resulting cells were collected by centrifugation (8,000 g, 10 minutes) and washed twice with 25 mM Tris-HCl buffer (pH 8.0) containing 0.02 mM pyridoxal phosphate, and then 50 ml of cell suspension was prepared. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 minutes), and the resulting supernatant was ultra-centrifuged (200,000 g, 30 minutes). The resulting supernatant was dialyzed using the same buffer, thus obtaining a cell-free extracted solution.
(2) Anion-Exchange Chromatography
The cell-free extracted solution obtained in the aforementioned (1) was applied in ResourceQ columns (Amersham Biosciences), which had been previously equilibrated with 25 mM tris-HCl buffer (pH8.0) containing 0.02 mM pyridoxal phosphate, and the enzyme was eluted by a linear concentration gradient of 0-1M sodium chloride. This process was conducted three times by dividing the cell-free extracted solution into three aliquots.
(3) Hydrophobic Interaction Chromatography
Active fractions of the enzyme obtained in the aforementioned (2) were dialyzed in 25 mM tris-HCl buffer (pH7.4) containing 0.02 mM pyridoxal phosphate (hereinafter, simply referred to as the buffer I), and mixed with the buffer I containing an equivalent amount of 2M ammonium sulfate, and then applied to Phenyl-Sepharose columns (Amersham Biosciences) which had been previously equilibrated with the buffer I containing 1M ammonium sulfate. Then, the enzyme was eluted by the linear concentration gradient of 1-0M ammonium sulfate.
(4) Hydroxyapatite Column Chromatography
The active fractions obtained in the aforementioned (3) were dialyzed with 2.5 mM potassium phosphate buffer (pH 7.0) containing 0.02 mM pyridoxal phosphate, and then applied in the CellulofineHAp columns (SEIKAGAKU Corp.) which had been previously equilibrated with the same buffer. The enzyme was eluted in 2.5-500 mM potassium phosphate buffer (pH7.0).
The active fractions of the enzyme having 0.72 U/mg of relative activity, which were obtained in this manner, were electrophoresed with SDS-polyacrylamide, and the gel was stained with Coomassie brilliant blue staining fluid. A homogeneous band appeared at a position of approximately 47,000 of molecular weight.
Example 3
Determination of the Amino Acid Sequence and the Encoding Nucleotide Sequence of 2-Methyl Serine Hydroxymethyl Transferase Derived from and Native to the Ralstonia sp. A11 (AJ110405) Strain
100 pmol of purified enzyme, which had been prepared in Example 2, was electrophoresed in SDS-polyacrylamide, transcribed on a PVDF membrane, and then put in a protein sequencer to determine 30 amino acids (SEQ ID NO: 1).
Second, 5 μg of genomic DNA derived from the Ralstonia sp. AJ110405 was cleaved with SalI (75 U), and then ligated to SalI cassettes in line with the method described in the manual supplied with the TaKaRa LA PCR in vitro Cloning Kit. Using the ligated mixture as a template, PCR (94° C.: 30 sec., 47° C.: 2 min., 72° C.: 1 min., 30 cycles) was performed with a combination of a cassette primer C1 and a primer ALD_RV_S1 (SEQ ID NO: 2). Subsequently, using the PCR reaction mixture as a template, the second PCR (94° C.: 30 sec., 55° C.: 2 min., 72° C.: 1 min., 30 cycles) was performed with a cassette primer C2 and a primer ALD_RV_S2 (SEQ ID NO: 3). Approximately 0.7 kb-length fragments which were amplified, were ligated to pGEM-Teasy (Promega) and used to transform Escherichia coli JM109.
Defining the nucleotide sequence of approximately 0.7 kb of fragments, the nucleotide sequence encoding the N terminal amino acid sequence of the objective protein was detected. Using approximately 0.3 kb-length gene fragments obtained by treating the plasmid with EcoRI/SphI as a probe, chromosomal DNAs were subject to Southern analysis after treatment with various types of restriction enzymes. When the chromosome DNAs were treated with SphI, a positive signal was confirmed in an approximately 2.4 kb region.
Subsequently, the chromosomal DNAs were treated with SphI, and then electrophoresed in an agarose gel, to purify the approximately 2.5 kb fragment. The fragment was then ligated to the pUC18 SphI site. Using this reaction mixture, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to perform colony hybridization to obtain positive colonies. A plasmid was extracted from the positive colonies. Using the resulting plasmid as pSKA04098, the nucleotide sequences of the inserted sequence were determined. An ORF (SEQ ID NO. 4) encoding 438 amino acids was found.
Example 4
Expression of 2-Methyl Serine Hydroxymethyl Transferase Gene Derived from and Native to the Ralstonia Sp. A11 (AJ110405) in Escherichia coli 
Using pSKA04098 as a template, PCR was performed with the primer Ral_Eco (SEQ ID NO: 6) and the primer Ral_ter_Pst (SEQ ID NO: 7) to amplify a 1.3 kb region of 2-methyl serine hydroxymethyl transferase. The amplified sequence was treated with EcoRI/PstI, and then ligated to pUC18 which had been previously treated with EcoRI/PstI, to transform Escherichia coli JM109. The transformant having plasmid (pRal2) containing the objective gene fragments was obtained and designated JM109/pRal2.
JM109/pRal2 was pre-cultured in the LB culture medium containing 100 mg/l ampicillin at 37° C. for 16 hours. 0.15 ml of pre-cultured solution was inoculated into 3 ml LB culture medium containing 100 mg/l ampicillin and cultured at 37° C. One hour after the onset, IPTG was added so that the final concentration thereof reached 1 mM, and then the mixture was further cultured for four hours. The resulting cells were collected by centrifugation and washed with the 50 mM phosphoric acid buffer (pH 7.4) containing 0.1 mM pyridoxal phosphate.
A cell suspension was then prepared using 0.3 mL of the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant as a cell-free extracted solution. 2-methyl serine hydroxymethyl transferase activity was measured in the supernatant. The measured value was 0.03 U/mg. On the other hand, in the case of using a cell-free extracted solution obtained by the aforementioned method using the transformant JM109/pUC18, which is a transformant obtained by introducing pUC18 into JM109, the measured activity thereof was below the detection limit.
Example 5
Production of α-Methyl-L-Serine with 2-Methyl Serine Hydroxymethyl Transferase Derived from Ralstonia Sp. A11 (AJ110405)
50 μl of purified enzyme solution prepared in Example 2 was added to a solution of 100 mM formaldehyde, 100 mM L-alanine, 0.1 mM pyridoxal phosphate, and 100 mM phosphoric acid buffer (pH7.4). The reaction was performed at 30° C. for 20 hours. As formaldehyde, the highest quality of formaldehyde liquid product [code No.: 16223-55] from Nakarai Tesk was used. After the reaction, 100 μl of 1 mM aqueous copper sulfate and 50 μl of water were added to 50 μl of the reaction mixture, and then HPLC analysis was performed using Sumichiral OA-6100 (Sumitomo Kagaku Analysis Center) (mobile phase: 0.5 mM aqueous copper sulfate, column temperature: 30° C., flow rate: 1 ml/min., detection: UV215 nm). The result showed that 27.5 mM α-methyl-L-serine was produced but no peak attributed to α-methyl-D-serine was detected. As a reference standard, α-methyl-L-serine [Code NO: 29001-2500], α-methyl-D-serine [Code NO: 29002-2500] from Acros Organics were used.
Example 6
Production of α-Methyl-L-Serine Using the 2-Methyl Serine Hydroxymethyl Transferase Gene-Expressed Escherichia coli Derived from Ralstonia Sp. A11 (AJ110405)
JM109/pRal2 was cultured in LB medium containing 100 mg/l at 30° C. for 24 hours, and further cultured in the LB medium containing 100 mg/l and 0.5 mM IPTG at 34° C. for 16 hours. The cells obtained in 400 ml of the cultured medium were collected by centrifugation, and then washed with the 100 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphate. The resulting cells were suspended in 100 ml of reaction mixture (300 mM L-alanine, 0.1 mM pyridoxal phosphate, 100 mM phosphoric acid buffer (pH7.4)). 50.5 ml of 600 mM aqueous formaldehyde was added to the reaction mixture at 30° C. over 24 hours while stirring. As formaldehyde, the highest quality of formaldehyde liquid product [code No.: 16223-55] from Nakarai Tesk was used. After the adding process, 50 μl of 1 mM aqueous copper sulfate and 100 μl of water were added to 50 μl of the reaction mixture, and HPLC analysis was performed using Sumichiral OA-6100 (Sumitomo Kagaku Analysis Center) (mobile phase: 0.5 mM aqueous copper sulfate, column temperature: 30° C., flow rate: 1 ml/min., detection: UV215 nm). The result showed that 27.0 mmol α-methyl-L-serine was produced but no peak attributable to α-methyl-D-serine was detected.
Example 7
Acquisition of 2-Methyl Serine Hydroxymethyl Transferase Gene Derived from Variovorax paradoxus B2-B2 (AJ110406)
In line with the same manner described in Example 3, an ORF domain derived from Ralstonia sp. AJ110405 was amplified by PCR. Using the resulting PCR product as a probe, genomic DNA of Variovorax paradoxus B2-B2 was subject to Southern analysis after treatment with PstI. A positive signal was found in a region of approximately 2 kb length.
Subsequently, the genomic DNA of Variovorax paradoxus B2-B2 was treated with PstI and electrophoresed in an agarose gel. Approximately 2 kb of fragments were purified and ligated to the pUC118 PstI site. Using this reaction mixture, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to hybridize colonies to collect positive colonies. A plasmid was extracted from the positive colonies. Using the resulting plasmid as pUCB2-B2, the nucleotide sequence of the inserted sequence was determined. The presence of an ORF of 441 amino acids (SEQ ID NO. 8) was confirmed.
Subsequently, using pTV118N (Takara Bio) as a template, primers pTV118N_Nde (SEQ ID NO. 10) and pTV118N_Ndec (SEQ ID NO: 11) were used to obtain pTV118Nd using Quikchange site directed mutagenesis kit (Promega). The amplified fragment of 1.2 kb was obtained by PCR with the primers B2-B2_Nde (SEQ ID NO: 12) and B2-B2_ter_Pst (SEQ ID NO. 13) using pUCB2-B2 as a template. The resulting fragment was treated with NdeI/PstI and inserted into pTV118Nd NdeI/PstI site, which was designated pTVVHMT01. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pTVVHMT01.
JM109/pTVVHMT01 was pre-cultured in LB medium containing 100 mg/l ampicillin and 0.11 mM IPTG at 37° C. for 16 hours. The resulting cells were collected by centrifugation and washed with 50 mM phosphoric acid buffer (pH 7.4) containing 0.1 mM pyridoxal phosphate, and then a cell suspension was prepared with the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant as a cell-free extracted solution. 2-methyl serine hydroxymethyl transferase activity was measured in the supernatant. Generated formaldehyde was determined after reaction in the reaction mixture containing 50 mM Tris-HCl buffer (pH8.5), 10 mM α-methyl-L-serine, and 0.1 mM pyridoxal phosphate at a reaction temperature 30° C. The measured value was 9 mU/mg. On the other hand, when using a cell-free extracted solution obtained in line with the aforementioned method using the transformant JM109/pTV118Nd, which is a transformant obtained by introducing pTV118Nd into JM109, the measured activity thereof was below the detection limit.
Example 8
Acquisition of 2-Methyl Serine Hydroxymethyl Transferase Genes Derived from the Variovorax paradoxus NBRC15149
In line with the same manner described in Example 3, an ORF domain derived from Ralstonia sp. AJ110405 was amplified by PCR. Using the resulting PCR product as a probe, genomic DNA of Variovorax paradoxus NBRC 15149 was subjected to Southern analysis after treatment with PstI. A positive signal was found in a 2 kb-length region.
Subsequently, the genomic DNA of Variovorax paradoxus NBRC 15149 was treated with PstI and electrophoresed in an agarose gel. Approximately 2 kb of fragments were purified and ligated to the pUC118 PstI site. Using this reaction mixture, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to hybridize colonies to collect positive colonies. A plasmid was extracted from the positive colonies. Using the resulting plasmid as pUC15149, the nucleotide sequence of the inserted sequence was determined. The presence of an ORF of 440 amino acids (SEQ ID NO: 14) was confirmed. Using pUC15149 as a template, PCR was performed with primers 15149_Nde (SEQ ID NO: 16) and 15149_ter_Pst (SEQ ID NO: 17). An amplified fragment of 1.2 kb was obtained by PCR. The resulting fragment was treated with NdeI/PstI, and inserted into the pTV118Nd NdeI/PstI site, which was designated pTVVHMT02. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pTVVHMT02.
JM109/pTVVHMT02 was pre-cultured in LB medium containing 100 mg/l ampicillin and 0.1 mM IPTG at 37° C. for 16 hours. The resulting cells were collected by centrifugation and washed with 50 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphate, and then a cell suspension was prepared with the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant as a cell-free extracted solution. 2-methyl serine hydroxymethyl transferase activity was measured in the supernatant. The measured value was 13 mU/mg.
Example 9
Acquisition of 2-Methyl Serine Hydroxymethyl Transferase Genes Derived from the Variovorax paradoxus NBRC15150 Strain
In accordance with the same manner described in Example 3, an ORF domain derived from Ralstonia sp. AJ110405 was amplified by PCR. Using the resulting PCR product as a probe, genomic DNA of Variovorax paradoxus NBRC 15150 was subject to Southern analysis after treatment with PstI. A positive signal was found in a 2 kb-length region.
Subsequently, the genomic DNA of Variovorax paradoxus NBRC 15150 was treated with PstI and electrophoresed in the agarose gel. Approximately 2 kb of fragments were purified and ligated to the pUC118 PstI site. Using this reaction mixture, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to hybridize colonies to collect positive colonies. A plasmid was extracted from the positive colonies. Using the resulting plasmid as pUC15150, the nucleotide sequence of the inserted sequence was determined. The presence of an ORF of 440 amino acids (SEQ ID NO: 18) was confirmed. Using pUC15150 as a template, PCR was performed with primers 15150_Nde (SEQ ID NO: 20) and 15150_ter_Pst (SEQ ID NO: 21). The amplified fragment of 1.2 kb was obtained by PCR. The resulting fragment was treated with NdeI/PstI, and inserted into the pTV118Nd NdeI/PstI site, which was designated pTVVHMT03. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pTVVHMT03.
JM109/pTVVHMT03 was pre-cultured in the LB medium containing 100 mg/l ampicillin and 0.1 mM IPTG at 37° C. for 16 hours. The resulting cells were collected by centrifugation and washed with 50 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphate, and then a cell suspension was prepared with the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant as a cell-free extracted solution. 2-methyl serine hydroxymethyl transferase activity was measured in the supernatant. The measured value was 36 mU/mg.
Example 10
Acquisition of 2-Methyl Serine Hydroxymethyl Transferase Genes Derived from the Bosea sp. B2-R1 (AJ110407) Strain
In line with the same manner described in Example 3, an OFR domain derived from Ralstonia sp. AJ110405 was amplified by PCR. Using the resulting PCR product as a probe, genomic DNA of Bosea sp. B2-R1 was subject to Southern analysis after treatment with PstI. A positive signal was found in a 5 kb-length region.
Subsequently, the genomic DNA of the Bosea sp. B2-R1 strain was treated with PstI and electrophoresed in an agarose gel. Approximately 5 kb of fragments were purified and ligated to the pUC118 PstI site. Using this reaction mixture, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to hybridize colonies to collect positive colonies. A plasmid was extracted from the positive colonies. Using the resulting plasmid as pUCB2-R1, the nucleotide sequence of the insertion was determined. The presence of an ORF of 440 amino acids (SEQ ID NO: 22) was confirmed. Using pUCB2-R1 as a template, PCR was performed with primers B2-R1_Psh (SEQ ID NO: 24) and B2-R1_ter_Pst (SEQ ID NO: 25). An amplified fragment of 1.2 kb was obtained by PCR. The resulting fragments were treated with PshBI/PstI, and inserted into the pTV118 NdeI/PstI site, which was designated pTVBHMT. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pTVBHMT. Using pUCB2-R1 as a template, PCR was performed with primers B2-R1_Eco (SEQ ID NO: 26) and B2-R1_ter_Pst (SEQ ID NO: 25). The amplified fragment of 1.2 kb was obtained by PCR. The resulting fragment was treated with EcoRI/PstI, and inserted into pUC18 EcoRI/PstI site, which was designated pUCBHMT. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pUCBHMT.
JM109/pTVBHMT was pre-cultured in LB medium containing 100 mg/l ampicillin and 0.1 mM IPTG at 37° C. for 16 hours. The resulting cells were collected by centrifugation and washed with 50 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphate, and then a cell suspension was prepared with the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant as a cell-free extracted solution. 2-methyl serine hydroxymethyl transferase activity was measured in the supernatant. The measured value was 95 mU/mg. JM109/pUCBHMT was pre-cultured in LB medium containing 100 mg/l ampicillin and 0.1 mM IPTG at 37° C. for 16 hours. The resulting cells were collected by centrifugation and washed with 50 mM phosphoric acid buffer (pH 7.4) containing 0.1 mM pyridoxal phosphate, and then a cell suspension was prepared with the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant as a cell-free extracted solution. 2-methyl serine hydroxymethyl transferase activity was measured in the supernatant. The measured value was 318 mU/mg.
In the case of using a cell-free extracted solution obtained in line with the aforementioned method using the JM109/pUC18, the measured activity thereof was below the detection limit.
Example 11
Acquisition of 2-Methyl Serine Hydroxymethyl Transferase Gene Derived from Silicibacter pomeroyi DSM15171
Using genomic DNA of Silicibacter pomeroyi DSM15171 as a template, the amplified fragment of 1.3 kb including SEQ ID NO: 29 was obtained by PCR with primers Silici ATG EcoRI (SEQ ID NO: 27) and Silici_ter_Pst (SEQ ID NO: 28). The resulting fragment was treated with EcoRI/PstI, and inserted into pUC18 EcoRI/PstI site, which was designated pUCSHMT. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pUCSHMT.
JM109/pUCSHMT was pre-cultured in LB medium containing 100 mg/l ampicillin and 0.1 mM IPTG at 37° C. for 16 hours. The resulting cells were collected by centrifugation and washed with 50 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphate, and then a cell suspension was prepared with the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant as a cell-free extracted solution. 2-methyl serine hydroxymethyl transferase activity was measured in the supernatant. Separated formaldehyde was determined after reaction in the reaction mixture containing 50 mM Tris-HCl buffer (pH 7.4), 10 mM α-methyl-L-serine, and 0.1 mM pyridoxal phosphate at a reaction temperature 30° C. The measured value was 190 mU/mg.
Subsequently, using genomic DNA of Silicibacter pomeroyi DSM15171 as a template, the PCR product of approximately 1.3 kb length including SEQ ID NO: 29 was obtained by PCR with primers Silici ATG pQE30 BamHI (SEQ ID NO: 34) and Silici_ter_Pst (SEQ ID NO: 28). The resulting product was digested with BamHI-PstI to prepare DNA fragments, and the fragment was inserted into pQE30 BamHI-PstI site, thus obtaining a plasmid which was capable of forming 2-methyl serine hydroxymethyl transferase coupled with 6×His at the 5′ terminal thereof. The plasmid was designated pQE30SHMT. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pQE30SHMT.
The obtained JM109/pQE30SHMT was cultured in the LB medium containing 100 mg/l ampicillin (LB+amp) at 30° C. for 14 hours, and further cultured for three hours after adding 1 mM IPTG. The resulting cells were collected by centrifugation and washed with 50 mM phosphoric acid buffer (pH 7.4) containing 0.1 mM pyridoxal phosphate, and then a cell suspension was prepared with the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant using QIAexprssionist (QIAGEN) in accordance with the attached protocol thereof. The obtained protein was designated His fused SHMT.
Using the obtained His fused SHMT, a reaction was performed in a 100 μL solution containing 10 mM formaldehyde, 100 mM L-alanine, 0.1 mM pyridoxal phosphate, 100 mM phosphoric acid buffer (pH 7.4) at 30° C. for 10 min. As formaldehyde, the highest quality of formaldehyde liquid product [code No.: 16223-55] from Nakarai Tesk was used. After the reaction, 200 μl of 1 mM aqueous copper sulfate was added into 100 μl of the reaction mixture, and HPLC analysis was performed using Sumichiral OA-6100 (Sumitomo Kagaku Analysis Center) (mobile phase: 0.5 mM aqueous copper sulfate, column temperature: 30° C., flow rate: 1 ml/min., detection: UV215 nm). The result showed that 0.367 mM α-methyl-L-serine was produced but no peak attributable to α-methyl-D-serine was detected.
Example 12
Production of α-Methyl-L-Serine with Escherichia coli Expressing 2-Methyl Serine Hydroxymethyl Transferase Gene Derived from Variovorax paradoxus Strain
JM109/pTVVHMT01, JM109/pTVVHMT02, and JM109/pTVVHMT03 prepared in line with the aforementioned example were respectively pre-cultured in LB medium containing 100 mg/l ampicillin and 0.1 mM IPTG at 37° C. for 16 hours. The resulting cells were collected from 100 ml medium by centrifugation and washed with 100 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphate.
The resulting cells were respectively suspended in 100 ml of a reaction mixture (150 mM L-alanine, 0.1 mM pyridoxal phosphate, 100 mM phosphoric acid buffer (pH7.4)). 50.5 ml of 300 mM aqueous formaldehyde was added to the reaction mixture at 30° C. over 24 hours while stirring. As formaldehyde, the highest quality of formaldehyde liquid product [code No.: 16223-55] from Nakarai Tesk was used. After the adding process, 50 μl of 1 mM aqueous copper sulfate and 100 μl of water were added to 50 μl of the reaction mixture, and HPLC analysis was performed using Sumichiral OA-6100 (Sumitomo Kagaku Analysis Center) (mobile phase: 0.5 mM aqueous copper sulfate, column temperature: 30° C., flow rate: 1 ml/min., detection: UV215 nm). The results are shown in Tabbe 5. It was confirmed that α-methyl-L-serine was produced but no peak attributable to α-methyl-D-serine was detected.










TABLE 5







Strain
Yield of α-methyl-L-serine (mmol)



















JM109/pTVVHMT01
1.2



JM109/pTVVHMT02
5.3



JM109/pTVVHMT03
13.7










Example 13
Preparation of a Strain Expressing 2-Methyl Serine Hydroxymethyl Transferase Derived from Bosea Sp. B2-R1 (AJ110407)
Fragments of 0.3 kb containing a promoter region of the trp operon on the chromosomal DNAs of Eshcherichia coli W3110 were amplified with oligonucleotide primers of SEQ ID NO: 31 and NO: 32, and then the resulting DNA fragments were ligated into pGEM-Teasy vector (Promega). In the ligation solution, E. coli JM109 was transformed, and a strain which contained the objective plasmid, in which the trp promoter had been inserted in the opposite direction of the lac promoter, was selected from the ampicillin-resistant strains. Subsequently, this plasmid was ligated with a DNA fragment containing trp promoter treated by EcoO109I/EcoRI and a product obtained by treating pUC19 (Takara) with EcoO109I/EcoRI. In the ligation solution, E. coli JM109 was transformed, and a strain containing the objective plasmid was selected from the ampicillin-resistant strains. This plasmid was treated with HindIII/PvuII and the resulting DNA fragment was ligated with DNA fragment of O.7 kb prepared by treating pKK223-3 (Amersham Pharmacia) with HindIII/HincI and containing the TrrnB terminator. Using this ligation solution, Eshcherichia coli JM109 was transformed, and a strain containing the objective plasmid was selected from the ampicillin-resistant strains. The plasmid was designated ptrp2. Using this ptrp2 as a template, 0.3 kb fragments containing the trp promoter were amplified with primers (SEQ ID NO: 31 and 33). In order to replace the promoter region of the ptrp2 with the resulting PCR product, a fragment prepared by digesting the resulting PCR product with EcoO109I/NdeI was ligated with a product prepared by treating ptrp2 with EcoO109I/NdeI. Using the resulting products, Eshcherichia coli JM109 was transformed, and a strain containing the objective plasmid was selected from the ampicillin-resistant strains. This plasmid was designated ptrp4. Subsequently, pTWV228 (TaKaRa) was treated with NdeI, and then the terminal thereof was blunt-ended. The resulting product was treated with AatII, obtaining a fragment of 1.9 kb. The resulting fragment was ligated with a 0.4 kb fragment prepared by treating ptrp4 AatII/HindIII and a 0.7 kb fragment prepared by treating pKK223-3 with PvuII/HindIII. Using the resulting ligation solution, Escherichia coli JM109 was transformed, and a strain containing the objective plasmid was selected from the ampicillin-resistant strains. This plasmid was designated ptrp13.
Using genomic DNA of Bosea sp. B2-R1 as a template, PCR was performed with primers B2-R1_Psh (SEQ ID NO: 24) and B2-R1_ter_Pst (SEQ ID NO: 25). The amplified fragment of 1.2 kb was obtained by PCR. The resulting fragment was treated with PshBI/PstI, and inserted into the ptrp13 NdeI/PstI site, which was designated ptrp13BHMT. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/ptrp13BHMT.
JM109/ptrp13BMT, mentioned above, was cultured on LB agar medium (10 g/l peptone, 5 μl yeast extract, 10 μl NaCl) containing 100 μg/ml ampicillin at 30° C. for 24 hours. Subsequently, cells which were on one eighth of a plate were transferred to 50 mL LB medium (10 μl peptone, 5 μl yeast extract, 10 μl NaCl), and cultured at 30° C. for 16 hours on a shaker (120 rpm). Subsequently, 1 ml of the resulting culture was inoculated into a 300 ml medium containing the following composition, and then a batch culture was performed in a 1.0-liter volume fermentor while stirring at a revolution speed 700 rpm, and aeration (1/1 vvm). After the sugar was consumed, a 15 ml aliquot of the culture was inoculated into a 300 ml medium composed of the same composition, and then a culture was performed in the same type of fermentor under the conditions of stirring, aeration (1/1 vvm), sugar feeding and at 35° C. pH thereof was automatically adjusted to 7.0 by ammonium gas.
Composition of the Medium (g/l)
Glucose 25.0
MgSO4.7H2O 1.0
(NH4)2SO4 5.0
H3PO4 3.5
FeSO4 7aq 0.05
MnSO4 7aq 0.05 Thiamine HCl 0.001
Pyridoxyne HCl 0.01
GD113 0.1
Ampicillin 0.1
Glucose and magnesium sulfate were individually sterilized. The pH of other elements was adjusted at 5.0 with KOH.
Composition of Feeding Sugar Solution (g/l)
Glucose 500.0
pH Not adjusted
Example 14
Production of α-Methyl-L-Serine with 2-Methyl Serine Hydroxymethyl Transferase Derived from Bosea Sp. B2-R1 (AJ110407)
Using the 30 ml of the resulting culture of JM109/ptrp13BHMT prepared in accordance with the aforementioned Example 13, the reaction to produce α-methyl-L-serine with 2-methyl serine hydroxymethyl transferase was conducted. 150 ml of 2400 mM formaldehyde aqueous solution was added to the 300 ml culture (1200 mM L-alanine, 0.1 mM pyridoxal phosphate, and 100 mM phosphoric acid buffer (pH 7.4), 10% of the cultured mixture of JM109/ptrp13BHMT) at 30° C. over 48 hours while stirring. As formaldehyde, the highest quality of formaldehyde liquid product [code No.: 16223-55] from Nakarai Tesk was used. After the adding process, 950 μl of 1 mM aqueous copper sulfate was added to 50 ml of the resulting solution. After 5-fold dilution with water, HPLC analysis was performed using Sumichiral OA-6100 (Sumitomo Kagaku Analysis Center) (mobile phase: 0.5 mM aqueous copper sulfate, column temperature: 30° C., flow rate: 1 ml/min., detection: UV215 nm). The result showed that 327.3 mmol α-methyl-L-serine was produced but no peak attributable to α-methyl-D-serine was detected.
Example 15
Purification of α-Methyl-L-Serine
The cells are roughly removed from the resulting reaction mixture prepared in accordance with Example 14. 3.3 g sulfuric acid was added to the 451 g resulting reaction mixture (α-methyl-L-serine: 9.08%) to adjust to pH 3, and then dissolved proteins were flocculated by heating at 50° C. for 1 hour. The resulting product was filtered with 0.2 μm MF, obtaining a 482 g solution α-methyl-L-serine: 8.45%, D-alanine: 0.13%, L-alanine: 0.08%) including residual washing water. 165 g of this solution was diluted with water to 5% α-methyl-L-serine. After the dilution, the solution was fed into a resin column filled with 120 ml H-type strong-acid cation exchange resin (Bayel, Lewatit S-1468), thus adsorbing α-methyl-L-serine. After washing with twofold volume of water of the resin, 352 g of aqueous solution (Content of α-methyl serine: approximately 3.8%) was obtained by elution using 1 M ammonia water.
The resulting solution was evaporated under reduced pressure to roughly remove ammonia. The pH of the solution at this stage was approximately 8.2. To remove any remaining cations, the solution was passed through a column filled with 20 ml H-type weak-acid cation exchange resin (IONAC, A-365), thus obtaining 204 g flow-through solution including the washing solution, with a pH was 5.2. Subsequently, the flow-through solution was condensed. The condensing process was stopped when crystals began to precipitate out. At this moment, the volume weight of the solution was 35.55 g α-methyl-L-serine: 37.2%). Then, crystallization by adding poor solvent was performed by adding 67 g methanol at room temperature. Then, after maturing at 10° C. for 1 hour while stirring, crystals were separated and washed with 12 g of 75% methanol aqueous solution. The obtained wet crystal was dried under reduced pressure at 40° C., resulting in 12.13 g of dried crystal. The content of α-methyl-L-serine was 100.7% compared to a commercially available standard. The resulting crystal contained 0.06% D-alanine and 0.05% L-alanine as impurities.
Example 16
Production of α-Ethyl-L-Serine with Esherichia coli Expressing 2-Methyl Serine Hydroxymethyl Transferase Gene Derived from Bosea Sp
JM109/pUCBHMT as cell-enzyme was suspended in 100 ml solution mixture (150 mM L-2-amino-n-butyric acid, 0.1 mM pyridoxal phosphate, 100 mM phosphoric acid buffer (pH 7.4)). 50.5 ml of 300 mM aqueous formaldehyde was added to the reaction mixture at 30° C. over 24 hours while stirring. As formaldehyde, the highest quality of formaldehyde liquid product [code No.: 16223-55] from Nakarai Tesk was used. After the cell separation (8000 g, 10 min), the resulting mixture (50 ml containing 632 mg of 4.75 mmol α-ethyl-serine) was applied to Mega Bond Elut SCX (10G) (Varian, Inc) which had been previously activated with 50 ml methanol and equilibrated with 100 ml H2O. Then, after washing with 100 ml water, fractions of 2.5 ml were each eluted with 0.5 N—HCl. HPLC analysis was performed for each fraction to confirm the amount of α-ethyl-serine/(α-ethyl serine+L-2-amino-n-butyric acid), thus obtaining the separated fraction with more than 99%. Non-separated fractions were evaporated to dryness, and then dissolved into approximately 10 ml water. The pH of the resulting solution was adjusted to around pH 7.0 by NaOH, and again the separation process was performed in accordance with the same manner mentioned above. This operation was repeated twice to collect the separated fractions, and these separated fractions were evaporated to dryness. The resulting product was dissolved into approximately 100 ml water and anion exchange resin (DEAE-cellulose, whatman) was added therein, and its pH was adjusted to around 6.0. After that, the resin was removed by filtration. Acetone was dropped into the resulting filtrate to precipitate crystals. The precipitated crystals were dried, obtaining white crystals (348 mg, 2.6 mmol). The structure of the obtained crystals was determined by NMR spectral and ESI-MS analysis, and then the optical rotation thereof was measured by a optical rotation measuring device (DIP-370) manufactured by Nippon Bunko ([a]D20=−3.4±0.4 (c=1, 5N—HCl), [a]D20=−4.5±0.04 (C=10, 5N—HCl)). It was confirmed that the major product of the enzymatic reaction had a (−)-form, i.e., (s)-form in reference to values described in the literature (Journal of Peptide Science, 2001, 7, 619-625; Tetrahedron Letters, 1988, 29, 235-238).
After the cell separation (8000 g, 10 min), 5 mmol NaHCO3 was added to the resulting mixture (25 ml containing 316 mg of 2.38 mmol α-ethyl-serine), and the pH was adjusted to 9.5 under ice cooling. 2.38 mmol Benzoyl chloride dissolved in 10 ml acetone was dropped therein over 1 hour while maintaining the pH at 9-10. After that, the reaction was performed for 3 hours at room temperature, and then HCl was added therein to adjust to pH 2.0. After EtOAc (10 ml×3) extraction and dehydration with MgSO4, the reaction product was evaporated to dryness. According to HPLC analysis, it was confirmed that the residue included a large amount of benzoic acid. For that reason, the product was dissolved in methanol and separation was performed by TLC (PLC plate 20×20 cm, Silica gel 60F254 2 mm (Merck), developing solvent: EtOAc/AcOH=20/1). After the detection step by UV irradiation, silica gel was collected by scraping, and subjected to extraction with methanol (100 ml). The resulting product was evaporated to dryness, thus obtaining white crystals. The white crystals were crystallized again by the following steps: adding a small amount of water thereto and adjusting the pH to around 8.0 with NaOH to dissolve them; and dropping HCl and adjusting the pH to around 2.0, to obtain the crystals again. The resulting crystals were separated by filtration. After the filtered crystals were dried, they were dissolved in a small amount of 2-propanol, and then hexane was dropped therein to crystallize again, thus obtaining 110 mg standard product (0.46 mmol). The result of the HPLC analysis indicated 99% area. The structure was determined by NMR spectral and ESI-MS analysis, and then the optical rotation was measured ([α]D20=−11.4±0.2 (C=1, methanol)). It was confirmed that the major product of the enzymatic reaction had (−)-form, i.e., (s)-form in reference to values described in the literature (Journal of Peptide Science, 2001, 7, 619-625).
Example 17
Production of α-Methyl Threonine with 2-Methyl Serine Hydroxymethyl Transferase Derived from Ralstonia sp. A11 (AJ110405)
50 μl of purified enzyme solution prepared in accordance with Example 2 was added to a solution composed of 51 mM acetaldehyde, 50 mM L-alanine, 0.1 mM pyridoxal phosphate, and 100 mM phosphoric acid buffer (pH 7.4). The reaction was performed at 30° C. for 17.5 hours. After the reaction, a supernatant was prepared by centrifugation (18,000 g, 10 min, 4° C.). The peak attributed to the molecular ion of α-methyl threonine was detected by ESI-MS analysis in the obtained supernatant.
INDUSTRIAL APPLICABILITY
The method of the present invention is useful in industries involving in amino acid production. It is expected that the present invention would contribute to the production of various types of serine derivatives and optically active amino acids, and specifically, the method may be used in producing, for example, intermediates for drugs and medicals.
While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Each of the aforementioned documents is incorporated by reference herein in its entirety.
Free Text of Sequence Listing
SEQ ID NO: 1: primer
SEQ ID NO: 2: primer
SEQ ID NO: 3: primer
SEQ ID NO: 6: primer
SEQ ID NO: 7: primer
SEQ ID NO: 10: primer
SEQ ID NO: 11: primer
SEQ ID NO: 12: primer
SEQ ID NO: 13: primer
SEQ ID NO: 16: primer
SEQ ID NO: 17: primer
SEQ ID NO: 20: primer
SEQ ID NO: 21: primer
SEQ ID NO: 24: primer
SEQ ID NO: 25: primer
SEQ ID NO: 26: primer
SEQ ID NO: 27: primer
SEQ ID NO: 28: primer
SEQ ID NO: 31: primer
SEQ ID NO: 32: primer
SEQ ID NO: 33: primer
SEQ ID NO: 34: primer

## Claims

1. A method for producing an L-serine derivative of formula (III):



comprising reacting an L-α-amino acid of formula (I):




with an aldehyde of formula (II):




in the presence of an enzyme,
wherein R1 is selected from the group consisting of an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, wherein these groups may be either linear or branched and may have a substituent, and
wherein R2 is selected from the group consisting of a hydrogen, an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, wherein these groups may be either linear or branched and may have a substituent;
wherein said enzyme is a protein selected from the group consisting of:
(A) a protein comprising the amino acid sequence of SEQ ID NO: 23; and
(B) a protein comprising an amino acid sequence which has variation in the amino acid sequence of SEQ ID NO: 23, wherein said variation is selected from the group consisting of substitution, deletion, insertion, addition, inversion, and combinations thereof, of amino acids in said sequence, and wherein said protein is at least 90% homologous with the sequence of SEQ ID NO. 23 and is able to catalyze the reaction to form said L-serine derivative of formula (III).

2. The method for producing the L-serine derivative according to claim 1, wherein said enzyme is derived from and native to the microorganism Bosea.

3. The method for producing the L-serine derivative according to claim 1, wherein said L-α-amino acid is L-α-alanine, and said L-serine derivative is α-methyl-L-serine.

4. The method for producing the L-serine derivative according to claim 1, wherein said L-α-amino acid is L-2-amino-n-butyric acid, and said L-serine derivative is α-ethyl-L-serine.

5. The method for producing the L-serine derivative according to claim 1, wherein said L-α-amino acid is L-α-alanine, and said L-serine derivative is α-methyl-L-threonine.

6. The method of claim 1, wherein said protein is at least 95% homologous with the sequence of SEQ ID NO. 23 and is able to catalyze the reaction to form said L-serine derivative of formula (III).

7. A method for producing an L-serine derivative of formula (III):



comprising reacting an L-α-amino acid of formula (I):




with an aldehyde of formula (II):




in the presence of an enzyme,
wherein R1 is selected from the group consisting of an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, wherein these groups may be either linear or branched and may have a substituent, and
wherein R2 is selected from the group consisting of a hydrogen, an alkyl group with 1 to 6 carbons, an aryl group with 6 to 14 carbons, a cycloalkyl group with 3 to 10 carbons, an aralkyl group with 7 to 19 carbons, an alkoxyalkyl group with 2 to 11 carbons, a group containing a hetero atom in the carbon skeleton thereof, and a group containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, wherein these groups may be either linear or branched and may have a substituent;
wherein said enzyme is a protein selected from the group consisting of:
(A) a protein comprising the amino acid sequence encoded by the nucleotide sequence of SEQ ID NO: 22; and
(B) a protein comprising an amino acid sequence encoded by a nucleotide sequence that is at least 95% or more homologous with the sequence of SEQ ID NO: 22, and said protein is able to catalyze the reaction to form said L-serine derivative of formula (III).

8. The method for producing the L-serine derivative according to claim 6, wherein said enzyme is derived from and native to the microorganism Bosea.

9. The method for producing the L-serine derivative according to claim 6, wherein said L-α-amino acid is L-α-alanine, and said L-serine derivative is α-methyl-L-serine.

10. The method for producing the L-serine derivative according to claim 6, wherein said L-α-amino acid is L-2-amino-n-butyric acid, and said L-serine derivative is α-ethyl-L-serine.

11. The method for producing the L-serine derivative according to claim 6, wherein said L-α-amino acid is L-2-amino-n-butyric acid, and said L-serine derivative is α-ethyl-L-serine.