Patent Publication Number: US-2009233336-A1

Title: Process for producing chondroitin

Description:
TECHNICAL FIELD 
     The present invention relates to a novel production method for a chondroitin with a desired sugar chain length, and the like. 
     BACKGROUND ART 
     First, abbreviations used in the present application document will be described. 
     CH: chondroitin
 
CS: chondroitin sulfate
 
HA: hyaluronic acid
 
GlcUA: glucuronic acid
 
     GalNAc: N-acetylgalactosamine 
     GPC: gel permeation chromatography
 
HPLC: high performance liquid chromatography
 
K4CP: chondroitin polymerase derived from  Escherichia coli  K4 strain
 
D241K: a point mutant of K4CP comprising the amino acid sequence shown in SEQ ID NO: 2 in which the aspartic acid residue of amino acid number 241 in SEQ ID NO: 2 is replaced by a lysine residue. This enzyme substantially lacks an activity to transfer GalNAc, but maintains an activity to transfer GlcUA.
 
D521K: a point mutant of K4CP comprising the amino acid sequence shown in SEQ ID NO: 2 in which the aspartic acid residue of amino acid number 521 in SEQ ID NO: 2 is replaced by a lysine residue. This enzyme substantially lacks an activity to transfer GlcUA, but maintains an activity to transfer GalNAc.
 
MALDI-TOF-MS: Matrix Assisted Laser Desorption/Ionization time-of-flight mass spectrometry
 
UDP: uridine 5′-diphosphate
 
PA: aminopyridine
 
     A CH is a kind of glycosaminoglycan in which GlcUA and GalNac are linearly and alternately bound by a β1-3 linkage and a β1-4 linkage, respectively. CH is present as CS proteoglycan in a cartilage and many connective tissues in an animal body, and plays an important role in cell adherence, cell generation, cell differentiation, nerve cell extension, cartilage formation, bone formation, tissue regeneration, and the like. 
     Although a CH polymerase derived from an animal has been cloned, a CH cannot be synthesized by using the enzyme alone. Moreover, such an enzyme has a weak enzymatic activity, so use of such an enzyme does not sufficiently contribute to the efficient industrial production of CH sugar chains. On the other hand, K4CP has also been cloned, and it is known that the enzyme alone has an activity to synthesize a CH (Patent Document 1 and Non-patent Document 1). 
     K4CP is an enzyme having two active sites for sugar transfer, and allows sugar chains to extend by using UDP-GlcUA and UDP-GalNAc as donors, respectively. By changing a reaction time and an addition amount of substrates, a size (sugar chain length) of a synthesized CH can be adjusted to a certain extent. However, since the obtained fraction is a mixture containing sugar chains each having a different molecular weight, a fraction consisting a CH having only a desired sugar chain length cannot be obtained. 
     Each of the two active sites for sugar transfer in K4CP bears activities to transfer the UDP-GlcUA and the UDP-GalNAc, respectively. It is also known that a mutant obtained by replacing an amino acid in one of the active sites for sugar transfer with another amino acid shows only a sugar transfer activity of the other sugar transfer site (Patent Document 2). 
     In addition, it is known that an HA oligosaccharide can be produced by using a point mutant of an HA synthase derived from  Pasteurella multocida  which is an animal-infectious bacterium, but production of a CH oligosaccharide and the like is not disclosed (Non-patent Document 2). 
     Patent Document 1: JP 2003-199583 A 
     Patent Document 2: JP 2005-65565 A 
     Non-patent Document 1: Ninomiya, T. et al., 2002, Journal of Biological Chemistry, Volume 277, No. 24, p. 21567-21575 
     Non-patent Document 2: Paul, L. DeAngelis et al., 2003, Journal of Biological Chemistry, Volume 278, No. 37, p. 35199-35203 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     An object of the present invention is to provide a method of producing a CH with a desired sugar chain length, a method of producing a fraction containing a CH with a substantially single sugar chain length, and the like. 
     Means for Solving the Problems 
     The inventors of the present invention intensively studied to solve the above-mentioned problems. As a result, the inventors have provided a method for producing a CH with a desired sugar chain length, a method for producing a fraction containing a CH with a substantially single sugar chain length, and the like by performing multiple specific steps alternately using a specific glycosyltransferase and the like, thereby the present invention has been completed. 
     That is, the present invention provides a method for producing a CH with a desired sugar chain length (hereinafter referred to as “Method 1 of the present invention”) comprising the steps of (a) and (b): 
     Step (a): a step of allowing a receptor substrate having a GlcUA residue at a non-reducing end thereof (a sugar chain obtained by the step (b) when the step (a) is performed after the step (b)), a GalNAc donor, and a GalNAc transferase to coexist in a reaction system; and 
     Step (b): a step of allowing a receptor substrate having a GalNAc residue at a non-reducing end thereof (a sugar chain obtained by the step (a) when the step (b) is performed after the step (a)), a GlcUA donor, and a GlcUA transferase to coexist in a reaction system, and the steps of (a) and (b) are performed alternately. 
     The present invention also provides a method for producing a fraction containing a CH with a substantially single sugar chain length (hereinafter referred to as “Method 2 of the present invention”) comprising the steps of (a) and (b): 
     Step (a): a step of allowing a receptor substrate with a substantially single sugar chain length, the substrate having a GlcUA residue at a non-reducing end thereof (a sugar chain obtained by the step (b) when the step (a) is performed after the step (b)), a GalNAc donor, and a GalNAc transferase to coexist in a reaction system; and 
     Step (b): a step of allowing a receptor substrate with a substantially single sugar chain length, the substrate having a GalNAc residue at a non-reducing end thereof (a sugar chain obtained by the step (a) when the step (b) is performed after the step (a)), a GlcUA donor, and a GlcUA transferase to coexist in a reaction system, and the steps of (a) and (b) are performed alternately. 
     The present invention also provides a method for producing a CH with a sugar chain length longer by one sugar than that of a receptor substrate (hereinafter referred to as “Method 3 of the present invention”) comprising only one of the steps (a) and (b) as defined in Method 1 of the present invention. 
     Hereinafter, Methods 1 to 3 of the present invention is together referred to as “the method of the present invention”. 
     Each of the GalNAc transferase in the step (a) and the GlcUA transferase in the step (b) of the method of the present invention is preferably an enzyme shown in the following (A). 
     (A) an enzyme comprising the amino acid sequence shown in SEQ ID NO: 2 
     Moreover, it is also preferable that the GalNAc transferase in the step (a) of the method of the present invention is an enzyme shown in the following (B), and the GlcUA transferase in the step (b) of the method of the present invention is an enzyme shown in the following (C). 
     (B) a mutant of the enzyme comprising the amino acid sequence shown in SEQ ID NO: 2, in which one to several amino acids in a region shown by amino acid numbers 435 to 539 in SEQ ID NO: 2 are replaced by another amino acid. 
     (C) a mutant of the enzyme comprising the amino acid sequence shown in SEQ ID NO: 2, in which one to several amino acids in a region shown by amino acid numbers 153 to 258 in SEQ ID NO: 2 are replaced by another amino acid. 
     Of these, a mutant of the enzyme, in which a “region shown by amino acid numbers 435 to 539” is a “region shown by amino acid numbers 519 to 521”, a “region shown by amino acid numbers 153 to 2581” is a “region shown by amino acid numbers 239 to 241”, and “one to several” is “1 to 3”, is preferable. Further, a mutant of the enzyme, in which only an amino acid of amino acid number 521 is replaced by another amino acid, and only an amino acid of amino acid number 241 is replaced by another amino acid, is more preferable. 
     It is also preferable that the method of the present invention further comprises a step of removing at least one of the transferase and the donor which are allowed to coexist in each of the steps (a) and (b) soon after each of the steps. In this case, it is preferable to remove only the transferase. 
     In addition, it is also preferable that the GalNAc donor used in the method of the present invention is UDP-GalNAc, and the GlcUA donor used in the method of the present invention is UDP-GlcUA. 
     “Coexistence” in the method of the present invention is performed preferably for 10 minutes to 24 hours under a condition of 10 to 50° C., more preferably for 30 minutes to 5 hours under a condition of 20 to 40° C., and still more preferably for 1 to 4 hours under a condition of 25 to 37° C. 
     Further, each of the transferases which are allowed to coexist in each of the steps (a) and (b) in the method of the present invention is preferably immobilized on a carrier. 
     Besides, the receptor substrate used in the method of the present invention is preferably a CH or its derivative. The derivative of the CH is preferably a CH to which PA is bound via a covalent bond. 
     EFFECTS OF THE INVENTION 
     The method of the present invention is very useful, because the method easily produces a CH with a desired sugar chain length and a fraction containing a CH with a substantially single sugar chain length at a low cost in an industrial scale, without substantially producing by-products. 
     In addition, the CH with a desired sugar chain length, the fraction containing a CH with a substantially single sugar chain length, and the like, which are produced by the present invention, are very useful substances for searching a physiological activity and the like depending on a change of a sugar chain, which has not been explored so far. The substances are also useful for materials for a pharmaceutical, food and beverage, cosmetics, and the like. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention will be hereinafter described by the best mode for carrying out the invention. 
     &lt;1&gt; Method 1 of the Present Invention 
     Method 1 of the present invention is a method for producing a CH with a desired sugar chain length comprising the steps of (a) and (b) described below and performing these steps alternately. 
     Step (a): a step of allowing a receptor substrate having a GlcUA residue at its non-reducing end (a sugar chain obtained by the step (b) when the step (a) is performed after the step (b)), a GalNAc donor, and a GalNAc transferase to coexist in a reaction system. 
     Step (b): a step of allowing a receptor substrate having a GalNAc residue at its non-reducing end (a sugar chain obtained by the step (a) when the step (b) is performed after the step (a)), a GlcUA donor, and a GlcUA transferase to coexist in a reaction system. 
     Method 1 of the present invention can produce a CH while controlling an increase of a sugar chain length, so that a CH with a desired sugar chain length can be easily produced. Therefore, Method 1 of the present invention also includes a concept of a method of controlling (managing) an increase of a CH sugar chain length and the like. It should be noted that “CH”, which is an object (object in which an increase of a CH sugar chain length is controlled) produced by Method 1 of the present invention, includes not only an original CH composed of a repeating unit of GlcUA-GalNAc alone but also derivatives of CH oligosaccharide and CH and the like. 
     The step (a) includes a step of allowing a receptor substrate having a GlcUA residue at its non-reducing end (a sugar chain obtained by the step (b) when the step (a) is performed after the step (b)), a GalNAc donor, and a GalNAc transferase to coexist. That is, the step (a) includes: transferring a GalNAc residue of the GalNAc donor to a GlcUA residue of the receptor substrate having a GlcUA residue at its non-reducing end by a GalNAc transferase as a reaction enzyme to produce a sugar chain which has a repeating unit of GlcUA-GalNAc as a non-reducing end and has a saccharide residue number longer by one more residue than the receptor substrate. 
     On the other hand, the step (b) includes a step of allowing a receptor substrate having a GalNAc residue at its non-reducing end (a sugar chain obtained by the step (a) when the step (b) is performed after the step (a)), a GlcUA donor, and a GlcUA transferase to coexist. That is, the step (b) includes: transferring a GlcUA residue of the GlcUA donor to a GalNAc residue of the receptor substrate having a GalNAc residue at its non-reducing end by a GlcUA transferase as a reaction enzyme to produce a sugar chain that has the repeating unit of GalNAc-GlcUA as a non-reducing end and has a saccharide residue number longer by one residue than the receptor substrate. 
     A “receptor substrate having a GlcUA residue at its non-reducing end” herein described is not particularly limited as long as the receptor substrate is a sugar chain (including its derivative) having a GlcUA residue at its non-reducing end. Further, a “receptor substrate having a GalNAc residue at its non-reducing end” is not particularly limited as long as the receptor substrate is a sugar chain (including its derivative) having a GalNAc residue at its non-reducing end. 
     As these receptor substrates, sugar chains each represented by the following general formulae (1) and (2) may be exemplified. 
       GlcUA-GalNAc-R 1   (1) 
       GalNAc-GlcUA-R 2   (2) 
     where—represents a glycoside linkage and R 1  and R 2  each represent an optional group, which are the same or different from each other. 
     As “R 1 ” and “R 2 ”, a sugar chain residue having a CH skeleton and a sugar chain residue having an HA skeleton may be exemplified. Examples of the “sugar chain residue having a CH skeleton” herein described include a CH residue and a CS residue. These sugar chain residues may be further bound with another chemical substance or the like. 
     In the method of the present invention, “GlcUA” and “GalNAc” are preferably D-GlcUA and D-GalNAc, respectively. The glycoside linkage between GlcUA and GalNAc (GlcUA-GalNAc) is preferably a β1-3 linkage, and the glycoside linkage between GalNAc and GlcUA (GalNAc-GlcUA) is preferably a β1-4 linkage. 
     A sugar chain size of the receptor substrate is not particularly limited, and may also range from a high molecular weight polysaccharide chain to an oligosaccharide having about 1 to 20 saccharides. Specific examples of the “receptor substrate having a GlcUA residue at its non-reducing end” include CH oligosaccharides such as CH disaccharide, CH trisaccharide, CH tetrasaccharide, CH pentasaccharide, CH hexasaccharide, CH heptasaccharide, CH octosaccharide, CH nonasaccharide, CH decasaccharide and a high molecular weight CH as a sugar chain in the formula (1), and a sugar chain represented by the general formula (1) having CS oligosaccharides such as CS disaccharide, CS trisaccharide, CS tetrasaccharide, CS pentasaccharide, CS hexasaccharide, CS heptasaccharide, CS octosaccharide, CS nonasaccharide, CS decasaccharide and a high molecular weight CS as R 1 , and having HA oligosaccharides such as HA disaccharide, HA trisaccharide, HA tetrasaccharide, HA pentasaccharide, HA hexasaccharide, HA heptasaccharide, HA octosaccharide, HA nonasaccharide, HA decasaccharide and a high molecular weight HA as R 1 . Specific examples of the “receptor substrate having a GalNAc residue at its non-reducing end” include CH oligosaccharides such as CH disaccharide, CH trisaccharide, CH tetrasaccharide, CH pentasaccharide, CH hexasaccharide, CH heptasaccharide, CH octosaccharide, CH nonasaccharide, CH decasaccharide and a high molecular weight CH as a sugar chain represented by the formula (2), and a sugar chain represented by the general formula (2) having CS oligosaccharides such as CS disaccharide, CS trisaccharide, CS tetrasaccharide, CS pentasaccharide, CS hexasaccharide, CS heptasaccharide, CS octosaccharide, CS nonasaccharide, CS decasaccharide and a high molecular weight CS as R 2 , and having HA oligosaccharides such as HA disaccharide, HA trisaccharide, HA tetrasaccharide, HA pentasaccharide, HA hexasaccharide, HA heptasaccharide, HA octosaccharide, HA nonasaccharide, HA decasaccharide and a high molecular weight HA as R 2 . 
     These receptor substrates can be produced by a known method, and also commercially available. In addition, as derivatives of these sugar chains, derivatives obtained by binding other chemical substances to these sugar chains can be exemplified. Kinds and the like of the other chemical substances that binds to these sugar chains are not particularly limited. As these chemical substances, PA is exemplified. Manners of binding of the chemical substances to the sugar chains are not limited. Examples thereof include a covalent bond. Of these, a manner in which PA is bound to a sugar chain via a covalent bond is preferable. A manner in which PA is bound to a reducing end of a sugar chain is more preferable. A manner in which PA is bound to a reducing end of a CH (including oligosaccharides of CH) via a covalent bond is most preferable. A sugar chain to which PA is bound via a covalent bond can be prepared by a method of amino-alkylating PA to bind to a reducing end of the sugar chain using a reductant. As the reductant, cyanoborohydride, a dimethylamino borane complex, a trimethylamino borane complex, or the like is preferably used. A method using a trimethylamino borane complex is particularly preferable. 
     In Method 1 of the present invention, one kind of sugar chain with a desired sugar chain length can be produced by using a receptor substrate composed of one kind of compound as such a receptor substrate. Alternatively, by using a plural kinds (preferably 2 to 5 kinds and more preferably 2 to 3 kinds) of receptor substrates, a plurality of sugar chains each containing desired sugar chain lengths derived from each of the receptor substrates may be produced. When the production of only CH decasaccharide (sugar chain length: 10 sugars) is desired, for example, one kind of CH oligosaccharide having a shorter sugar chain length than that of decasaccharide may be used as a receptor substrate. When a mixture of a CH octasaccharide (sugar chain length: 8 sugars) and a CH dodecasaccharide (sugar chain length: 12 sugars) is simultaneously produced, for example, CH oligosaccharides each having chain lengths of (8-n) sugars and (12-n) sugars (n represents an integer of 1 or more) may be used as receptor substrates. 
     Method 1 of the present invention is characterized by performing the steps (a) and (b) alternately. Therefore, a “receptor substrate having a GlcUA residue at its non-reducing end” in the step (a) means a “sugar chain obtained by the step (b)” when the step (a) is performed after the step (b). Similarly, a “receptor substrate having a GalNAc residue at its non-reducing end” in the step (b) means a “sugar chain obtained by the step (a)” when the step (b) is performed after the step (a). 
     A “GlcUA donor” used in Method 1 of the present invention is not limited as long as the donor is a molecule capable of donating a GlcUA residue to a sugar chain molecule, and a GlcUA nucleotide is preferable. As the GlcUA nucleotide, UDP-GlcUA, and dTDP (deoxythymidine5′-diphosphate)-GlcUA can be exemplified, and the UDP-GlcUA is preferable. 
     A “GalNAc donor” used in Method 1 of the present invention is not limited as long as the donor is a molecule capable of donating a GalNAc residue to a sugar chain molecule, and a GalNAc nucleotide is preferable. As the GalNAc nucleotide, and UDP-GalNAc, dTDP (deoxythymidine5′-diphosphate)-GalNAc can be exemplified, and the UDP-GalNAc is preferable. 
     These sugar nucleotides may be produced by a known method, or commercially available. 
     In addition, a “GalNAc transferase” used in Method 1 of the present invention is not limited as long as the enzyme transfers GalNAc, and an enzyme which does not substantially transfer GlcUA is preferable. Further, a “GlcUA transferase” used in Method 1 of the present invention is not limited as long as the enzyme transfers GlcUA, and an enzyme which does not substantially transfer GalNAc is preferable. Both transferases may be the same kind of enzyme or different kinds of enzymes. 
     When the same kind of enzyme is used as both of the transferases, the enzyme shown in the following (A) is preferable. 
     (A) an enzyme comprising the amino acid sequence shown in SEQ ID NO: 2. 
     On the other hand, when different kinds of enzymes are used as the enzymes, it is preferable that a GalNAc transferase in the step (a) of the method of the present invention is an enzyme shown in the following (B), and a GlcUA transferase in the step (B) is an enzyme shown in the following (C). 
     (B) a mutant of the enzyme comprising the amino acid sequence shown in SEQ ID NO: 2, wherein one to several amino acids in the region shown by amino acid numbers 435 to 539 in SEQ ID NO: 2 are replaced by another amino acid. 
     (C) a mutant of the enzyme comprising the amino acid sequence shown in SEQ ID NO: 2, wherein one to several amino acids in the region shown by amino acid numbers 153 to 258 in SEQ ID NO: 2 are replaced by another amino acid. 
     SEQ ID NO: 1 shows the DNA sequence which is derived from  Escherichia coli  and encodes the amino acid sequence of SEQ ID NO: 2, together with the amino acid sequence. 
     Of these, preferable enzymes are enzymes in which “the region of amino acid numbers 435 to 539” is “the region of amino acid numbers 519 to 521”, “the region of amino acid numbers 153 to 258” is “the region of amino acid numbers 239 to 241”, and “one to several” is “1 to 3”. Among these enzymes, an enzyme in which only the amino acid of amino acid number 521 is replaced by another amino acid, and only the amino acid of amino acid number 241 is replaced by another amino acid is preferable. 
     Modes of amino acid substitution, such as amino acid substitutions in the region described above, the number of amino acid substitutions, and kinds of “another amino acid” described above are not limited as long as the enzyme after substitution maintains desired enzymatic activity. “Another amino acid” described above may be selected from natural amino acids and nonnatural amino acids. 
     When substitution of amino acids is performed by genetic engineering, “another amino acid” described above is preferably selected from the natural amino acids (glycine, L-alanine, L-valine, L-leucine, L-isoleucine, L-serine, L-threonine, L-aspartic acid, L-glutamic acid, L-asparagine, L-glutamine, L-cysteine, L-methionine, L-lysine, L-arginine, L-histidine, L-phenylalanine, L-tyrosine, L-tryptophan, and L-proline). 
     Particularly, in the case where only the amino acid of amino acid number 521 in SEQ ID NO: 2 (L-aspartic acid) is replaced by another amino acid and also in the case where only the amino acid of amino acid number 241 in SEQ ID NO: 2 (L-aspartic acid) is replaced by another amino acid, “another amino acid” is preferably L-lysine. Hereinafter, an enzyme obtained by replacing only the amino acid of amino acid number 521 in SEQ ID NO: 2 (L-aspartic acid) with L-lysine may be referred to as “D521K”. An enzyme obtained by replacing only the amino acid of amino acid number 241 in SEQ ID NO: 2 (L-aspartic acid) with L-lysine may be referred to as “D241K11”. 
     “D521K” and “D241K” can be obtained by the method described in the above-mentioned Non-patent Document 2. The “D241K” is an enzyme which transfers GlcUA to a non-reducing end of a receptor substrate to form a glycoside linkage by reacting a CH having a GalNAc residue at its non-reducing end as a receptor substrate with a GlcUA nucleotide (such as UDP-GlcUA) as a donor substrate, and is an enzyme (a mutant) which substantially lacks an activity of transferring GalNAc. The “D521K” is an enzyme which transfers GalNAc to a non-reducing end of a receptor substrate to form a glycoside linkage by reacting a CH having a GlcUA residue at its non-reducing end as a receptor substrate with a GalNAc nucleotide (such as UDP-GalNAc) serving as a donor substrate, and is an enzyme (a mutant) which substantially lacks an activity of transferring GlcUA. 
     These enzymes may be used as a free enzyme or may be used in a state of being immobilized on a carrier (a state of an immobilized enzyme). 
     In the steps (a) and (b), each of a method and a condition in which a receptor substrate, a sugar donor, and a glycosyltransferase are allowed to coexist is not limited as long as the molecules thereof are brought into contact with each other to thereby allow the glycosyltransferase to act on the receptor substrate and the sugar donor. Molecular weights and the like of them at the time of co-existence can be suitably set by those skilled in the art depending on the purpose and the like. 
     For example, “co-existence” is preferably performed at around a neutral pH (such as a pH of about 6.5 to 8.5), and is more preferably performed in a buffer solution having a buffer action at the pH. In addition, as a temperature and a time suitable for “co-existence”, there are exemplified: for 10 minutes to 24 hours under a condition of 10 to 50° C.; for 30 minutes to 5 hours under a condition of 20 to 40° C.; and for 1 to 4 hours under a condition of 25 to 37° C. In general, the longer the desired sugar chain is, the longer contact time is required, and another peak is sometimes observed. However, this problem can be solved by further extending the contact time. 
     The amounts of the glycosyltransferase and the receptor substrate at the time of “co-existence” is preferably set to about 1 nmol to 1 mmol, more preferably about 100 nmol of the receptor substrate with respect to 90 μl of the glycosyltransferase. Further, at the time of “co-existence”, the sugar donor may be set to 1 equivalent or more with respect to the receptor substrate. It is more preferable that the sugar donor is allowed to exist at 1.5 to 30 equivalents with respect to the receptor substrate to perform a complete reaction of the glycosyltransferase. It is more preferable that the sugar donor is allowed to exist at 2 to 10 equivalents with respect to the receptor substrate. 
     Alternatively, “co-existence” may be also performed by: immobilizing the glycosyltransferase on a suitable carrier (such as beads, an ultrafiltration membrane, and a dialysis membrane); and continuously bringing the carrier into contact with a solution containing the sugar donor and the receptor substrate. Therefore, a column-type reactor, a membrane-type reactor, or the like can be adopted. Further, the method shown in WO 00/27437 can be also used, in which a receptor substrate is immobilized on a carrier to perform a transferase reaction. Still further, a bioreactor or the like which regenerates (synthesizes) a sugar donor may be used in combination. 
     Method 1 of the present invention may further comprise other steps as long as it comprises at least both of the steps (a) and (b). For example, it is preferable that Method 1 of the present invention further comprises a step of removing at least one of the transferase and the donor being allowed to coexist in each of the steps (a) and (b) soon after the steps (a) and (b) in Method 1 of the present invention has been performed. In this case, it is preferable that only the transferase is removed. 
     The term “remove” in Method 1 of the present invention means to remove an action of a molecule from the co-existence system. Therefore, the term “remove” includes, needless to say, physically removing molecules themselves, and also includes a mode in which the action of the molecule is removed by deactivating the molecules. 
     A method of removing at least one of a transferase and a donor is not particularly limited. In the case of removing the transferase, which is immobilized on a solid phase; the solid phase is removed by a proper method, thereby the transferase can be removed. The donor can be removed by using, for example, gel filtration chromatography or an ultrafiltration membrane. 
     However, the reaction for producing a sugar chain with a sugar residue number longer by one residue than that of the receptor substrate in the steps (a) and (b) of Method 1 of the present invention can be controlled by reaction conditions (such as a reaction time and the like) as described in the examples shown below, so it is not essential to remove at least one of the transferase and the donor that were allowed to coexist in each of the steps so as to perform each reaction independently. 
     Therefore, the degree of “removal” is not necessarily 100%, and the degree can be suitably set by those skilled in the art depending on the purpose and the like. 
     For removal of the glycosyltransferase, for example, the glycosyltransferase may be deactivated by heat. When the glycosyltransferase is immobilized on a carrier, the removal may be performed by physically removing the carrier. The physical removal of the carrier may be easily performed by using a filtration membrane or the like or conducting centrifugation or the like. 
     Furthermore, it is needless to say that Method 1 of the present invention may further comprise a step of purifying the CH (with a desired sugar chain length) obtained by Method 1 of the present invention and a step of performing quality check. 
     Method 1 of the present invention is characterized by performing the steps (a) and (b) alternately. Therefore, the steps (a) and (b) may be performed alternately starting from the step (a) (for example, step (a), step (b), step (a), step (b), . . . ), and may be performed alternately starting from the step (b) (for example, step (b), step (a), step (b), step (a), . . . ). It should be noted that the term “alternately” also includes a case where the reaction is terminated only by performing two steps (for example, a case where a set of step (a) and step (b) is performed, and the reaction is finished and a case where a set of step (b) and step (a) is performed, and the reaction is finished). 
     One of the step (a) and step (b) is performed once, thereby a sugar chain is extended by one saccharide. Therefore, a CH with a desired sugar chain length can be produced by appropriately setting the number of each of the steps “alternately” performed. Those skilled in the art can suitably set and control the number of each of the steps to be alternately performed on the basis of the condition of co-existence of each molecule in each of the steps described above. 
     A product produced by Method 1 of the present invention (a CH with a desired sugar chain length) may be in the state of a solution or in the state of a solid (such as a powder or a frozen solution). 
     &lt;2&gt; Method 2 of the Present Invention 
     Method 2 of the present invention is a method for producing a fraction containing a CH with a substantially single sugar chain length, which comprises the steps (a) and (B) described below and these steps are performed alternately: 
     step (a): a step of allowing a receptor substrate with a substantially single sugar chain length having a GlcUA residue at its non-reducing end (a sugar chain obtained by the step (b) when the step (a) is performed after the step (b)), a GalNAc donor, and a GalNAc transferase to coexist; and 
     step (b): a step of allowing a receptor substrate with a substantially single sugar chain length having a GalNAc residue at its non-reducing end (a sugar chain obtained by the step (a) when the step (b) is performed after the step (a)), a GlcUA donor, and a GlcUA transferase to coexist. 
     Method 2 of the present invention is a method for producing a fraction containing a CH with a substantially single sugar chain length, and can be performed by “using only one kind” of the “receptor substrates” in Method 1 of the present invention. 
     Therefore, Method 2 of the present invention is the same as Method 1 of the present invention except that the target of production is “a fraction containing a CH with a substantially single sugar chain length”, and except that each of a receptor substrate having a GlcUA residue at its non-reducing end and a receptor substrate having a GalNAc residue at its non-reducing end has “substantially single sugar chain length”. Thus, a reaction, an enzyme, and reactants themselves such as a substrate having a GlcUA residue at its non-reducing end and a substrate having a GalNAc residue at its non-reducing end used in Method 2 of the present invention are the same as those used in Method 1 of the present invention. 
     Here, the term “substantially single” means that when a fraction is analyzed by MALDI-TOF-MS, the height of a peak derived from a sugar chain with a specific sugar chain length accounts for 70% or more of the sum of the heights of the total peaks including that peak. Analysis conditions by MALDI-TOF-MS are shown in Examples described below. 
     In a reaction for producing a sugar chain with a sugar residue number longer by one residue than that of a receptor substrate in the steps (a) and (b) of Method 2 of the present invention, it is not essential to remove at least one of the transferase and the donor that were allowed to coexist in each of the steps so as to perform each reaction independently, similarly as in Method 1 of the present invention. It is preferable that each of the reactions is performed after at least one of the transferase and the donor is removed substantially 100%. The method of removing at least one of the transferase and the donor is the same as Method 1 of the present invention. 
     Here, the term “removed substantially 100%” means that when a step of producing a sugar chain with a sugar residue number longer by only one residue is performed after the transferase or the substrate is removed, at least one of the transferase and the donor is removed to the extent that the peak of a sugar chain with a sugar residue number longer by only one residue is not substantially detected by MALDI-TOF-MS (substantially neglectable). For example, “removed substantially 100%” includes the condition shown in Example 3 (2) where D521K is not used (in this case, the transferase is removed), and the peak of PA-CH7 is not substantially detected (substantially neglectable), specifically, in the condition, PA-CH6 (100 nmol) is dissolved in a Tris-HCl buffer solution containing 1.2 mM of 20 mM manganese chloride and 150 mM NaCl, then 10 μl of 50 mM MUDP-GalNAc is added thereto, and the mixture is shaken at 30° C. for 2 hours, followed by purification and freeze-drying to obtain a fraction, which was then subjected to MALDI-TOF-MS. 
     &lt;3&gt; Method 3 of the Present Invention 
     Method 3 of the present invention is a method for producing a CH with a sugar chain length longer by one than that of a receptor substrate, and comprises only one of the steps (a) and (b) described in Method 1 of the present invention. 
     Method 3 of the present invention is a method for producing a CH with a sugar chain length longer by one than that of a receptor substrate, in which only one of the steps (a) and (b) in Method 1 of the present invention is performed without alternately performing the steps (a) and (b). 
     Therefore, Method 3 of the present invention is the same as Method 1 of the present invention except that the target of production is “a CH with a sugar chain length longer by one sugar than that of a receptor substrate”, and except that only one of the steps (a) and (b) in Method 1 of the present invention is performed. Thus, a reaction, an enzyme, a reactant, and the like in each step are the same as in Method 1 of the present invention. 
     Hereinafter, the present invention will be described in detail more specifically by referring to Examples. 
     (Analysis Method) 
     A CH and its derivatives obtained by Examples below were subjected to MALDI-TOF-MS (AutoFlex manufactured by Bruker Daltonics) for a structural analysis. The analysis was performed in a negative mode for detecting a generated anion, and the CH and its derivatives were analyzed in a reflection mode. 
     (Preparation of Target) 
     1 μl of the obtained specimen (containing 20 to 100 pmole of CH) and 10 mg/ml of DHB (2,5-dihydroxy-benzoic acid) were mixed in 1 μl of 50% acetonitrile solution. 1 μl of the resultant mixture was spotted on a target plate, followed by drying by immediately blowing a nitrogen gas. 
     Example 1 
     Immobilization of the Enzyme 
     To NHS-activated Sepharose Beads (manufactured by Amersham Biosciences Co., Ltd., 0.1 ml), 1 ml of a physiologic phosphate buffer solution (pH of 7.2) (hereinafter referred to as “PBS”) containing 0.5 mg of D241K or D521K (each obtained according to the examples of JP 2005-65565 A) and glycerol (final concentration of 20%) were added, followed by shaking at 4° C. for 6 hours. After the reaction, 4 μl of 1 M ethanol amine was added thereto, and followed by shaking at 4° C. for 1 hour. Then, washing was performed sequentially with 20 mM Tris-HCl buffer solution (pH of 8.0) three times, with 20 mM sodium acetate buffer solution (pH of 4.0) three times, and with 20% glycerol-PBS three times to thereby the immobilized enzymes for each of D241K and D521K were prepared. The obtained immobilized enzymes were suspended with 20% glycerol-PBS and then stored at 4° C. 
     By using 10 μl each of the obtained immobilized enzymes together with CH hexasaccharide and UDP-[ 3 H]GalNAc as substrates, GalNAc transfer activity was measured. By using 10 μl each of the obtained immobilized enzymes together with CH heptasaccharide and UDP-[14C]GlcUA as substrates, GlcUA transfer activity was measured. As a result, it was confirmed that the immobilized enzyme D241K (hereinafter referred to as D241K beads) retained only GlcUA transfer activity, and the immobilized enzyme D521K (hereinafter referred to as D521K beads) only retained GalNAc transfer activity. 
     Example 2 
     Production of CH Oligosaccharide to which PA is Bound by Covalent Bond (Pyridylaminated) 
     (1) Production of CH6 (CH Hexasaccharide) and CH7 (Heptasaccharide) 
     Hyaluronidase derived from sheep testis (Sigma-Aldrich Corporation) was added to a CH obtained by chemical desulfation of CS (manufactured by SEIKAGAKU CORPORATION) to perform limited degradation of the CH in a sodium acetate buffer solution containing NaCl, thereby oligosaccharides composed of even number saccharides and having a GlcUA residue at its non-reducing end were obtained. The obtained oligosaccharides were purified by gel filtration and iron-exchange column to collect a fraction corresponding to CH6. The obtained fraction was freeze-dried. The obtained fraction was subjected to an uronic acid content analysis (carbazole method), HPLC (GPC), MALDI-TOF-MS, a disaccharide analysis after chondroitinase treatment. As a result, it was confirmed that the obtained fraction was hexasaccharide having a GalNAc residue at its reducing end and a GlcUA residue at its non-reducing end. 
     Furthermore, β-glucuronidase (SIGMA) was added to a mixture of CH oligosaccharides composed of multiple kinds of even number saccharides obtained by subjecting a CH to a hyaluronidase treatment in the same manner as described above. The mixture was left standing at 37° C. for 18 hours in a sodium acetate buffer solution containing NaCl. The reaction solution was subjected to a purification treatment in the same manner as that described above. A fraction corresponding to CH7 was collected and then freeze-dried. The obtained fraction was subjected to the same analyses described above. As a result, it was confirmed that the obtained fraction was CH7 having GalNAc at its reducing end and GalNAc at its non-reducing end. 
     (2) Production of CH6 to which PA is Bound by Covalent Bond (PA-CH6) 
     The CH6 (10 mg) obtained by the procedure (1) was dissolved in 1 ml of water, and 1 ml of PA aqueous solution adjusted to pH of 5.6 with hydrochloric acid and 1 ml of methanol solution of trimethyl amino borane complex (Aldrich) were added thereto, followed by reaction at 70° C. for 3 days under sealing. The reaction solution was concentrated under reduced pressure, and freeze-dried, which was then dissolved in 0.1 ml of water again. Subsequently, the solution was passed through Dowex 50 WX8 cationic exchange resin (manufactured by The Dow Chemical Company), and was subjected to gel filtration chromatography (flow rate: 2 ml/minute) with Superdex 30 HR 16/60 column (Amersham) using 0.2 M ammonium acetate as a development solution. The solution to be detected was monitored with a fluorescence detector (Ex: 310 nm, Em: 370 nm), and fractions containing PA-CH6 were collected. The fractions were further subjected to ion-exchange chromatography by Linear Gradient method using 30 to 200 mM of KH 2 PO 4  with SAX Magnum 9/25HPLC column (manufactured by Whatman, Inc.) for purification, thereby PA-CH6 was obtained. The PA-CH6 was analyzed in the same manner as the procedure (1) to confirm the structure and purity of the PA-CH6 ( FIG. 1 ). 
     Example 3 
     Production of Pyridylaminated-Oligosaccharide with Desired Sugar Chain Length 
     (1) Setting of Reaction Time 
     The PA-CH6 (100 nmol) obtained in Example 2 (2) was dissolved in 1.2 ml of 50 mM Tris-HCl buffer solution (pH of 7.2) containing 20 mM manganese chloride and 150 mM NaCl, and the mixture was added to a container containing the D521K beads obtained in Example 1. 10 μl of 50 mM UDP-GalNAc and 5 μmol (0.1 μCi) of UDP-[ 3 H]GalNAc were added into the container. The container was shaken at 30° C., and 1 hour later, the reaction solution was subjected to separation with gel filtration chromatography using Superdex Peptide HR 10/30 column. A transfer amount of GalNAc was measured by a scintillation counter, which confirmed that the sugar transfer reaction was almost perfectly completed one hour later. Based on the result, the reaction time was set as 2 hours. 
     (2) Production of PA-CH7 
     In the same manner as Example 3 (1), the PA-CH6 obtained in Example 2 (2) was dissolved in the same Tris-HCl buffer solution as described above, and the mixture was added into a container containing D521K beads obtained in Example 1. UDP-GalNAc was added into the container, followed by shaking at 30° C. for 2 hours. The reaction solution (1.2 ml) was subjected to filtration with a filter (Ultra Free CL, manufactured by Millipore Corporation, pore diameter of 0.45 μm) to remove the enzyme-immobilized beads, thereby a filtrate containing PA-CH7 was obtained. The filtrate was used as it is for the following saccharide transfer reaction. 
     The filtrate was subjected to gel filtration chromatography using Superdex Peptide HR 10/30 column to purify PA-CH7, and the purified PA-CH7 was freeze-dried. The purified fractions were subjected to MALDI-TOF-MS analysis, which confirmed that the purified fractions were high-purity PA-CH7 ( FIG. 2 ). 
     (3) Production of PA-CH8 (Pyridylaminated-CH Octosaccharide) 
     The PA-CH7 solution obtained in Example 3 (2) was added into a container containing D241K beads, and 10 μl of 50 mM UDP-GlcUA was added thereto, followed by shaking at 30° C. for 2 hours. The reaction solution was treated in the same manner as the procedure (2) to remove the enzyme-immobilized beads, thereby a filtrate containing PA-CH8 was obtained. The filtrate was used as it is for producing PA-CH9 in the production of PA-CH9 to PA-CH16 (pyridylaminated-CH nonasaccharide to pyridylaminated-CH hexadecasaccharide) shown below. Purification and analysis of PA-CH8 were carried out in the same manner as described above ( FIG. 3 ). 
     Production of PA-CH9 to PA-CH16 
     PA-CH9 was obtained by performing the same operation as in the procedure (2) using the filtrate containing the PA-CH8. PA-CH10 was obtained by performing the same operation as in the procedure (3) using the filtrate containing the PA-CH9. In the same manner as described above, the operations in the procedures (2) and (3) were repeated to thereby obtain pyridylaminated-CH oligosaccharides in which the sugar chain length was extended one by one. The thus obtained PA-CH9 to PA-CH16 were purified and analyzed in the same manner as described above ( FIGS. 4 to 11 ). 
     Example 4 
     Synthesis of Oligosaccharides by Continuous Sugar Chain Extension 
     By using the CH6 obtained in Example 2 (1), the reactions were alternately performed in the same manner as in Example 3 until sugar chains with a desired sugar chain length were obtained, thereby each of CH7 to CH16 (CH heptasaccharide to CH hexadecasaccharide) was produced. Purification and analysis of CH7 to CH16 were carried out in the same manner as described above. It was confirmed that each of CH7 to CH16 was obtained. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates MALDI-TOF-MS spectrum of PA-CH6. 
       FIG. 2  illustrates MALDI-TOF-MS spectrum of PA-CH7. 
       FIG. 3  illustrates MALDI-TOF-MS spectrum of PA-CH8. 
       FIG. 4  illustrates MALDI-TOF-MS spectrum of PA-CH9. 
       FIG. 5  illustrates MALDI-TOF-MS spectrum of PA-CH10. 
       FIG. 6  illustrates MALDI-TOF-MS spectrum of PA-CH11. 
       FIG. 7  illustrates MALDI-TOF-MS spectrum of PA-CH12. 
       FIG. 8  illustrates MALDI-TOF-MS spectrum of PA-CH13. 
       FIG. 9  illustrates MALDI-TOF-MS spectrum of PA-CH14. 
       FIG. 10  illustrates MALDI-TOF-MS spectrum of PA-CH15. 
       FIG. 11  illustrates MALDI-TOF-MS spectrum of PA-CH16.