# Patent

## Title
Glycopeptides produced using Amycolatopsis orientalis glycosyltransferase gtfE

## Abstract

The invention provides isolated nucleic acid compounds encoding a glycosyltransferase enzyme of Amycolatopsis orientalis. Also provided are vectors carrying genes that encode said enzyme, transformed heterologous host cells for expressing said enzyme, and methods for producing glycopeptide compounds using the cloned genes that encode said enzyme.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a divisional of application Ser. No. 09/789,261 filed Feb. 20, 2001, now U.S. Pat. No. 6,566,100, which is a divisional of application Ser. No. 09/198,212, filed Nov. 23, 1998, now U.S. Pat. No. 6,232,102; which is a divisional of application Ser. No. 09/120,053, filed Jul. 21, 1998, now U.S. Pat. No. 5,932,464; which is a divisional of application Ser. No. 08/926,258, filed Sep. 5, 1997, now U.S. Pat. No. 5,871,983; which claims the benefit of 60/026,055, filed Sep. 13, 1996, the contents of each of which are herein incorporated by reference in their entirety.


BACKGROUND OF THE INVENTION
This invention relates to recombinant DNA technology. In particular the invention pertains to the cloning of a glycosyltransferase gene from Amycolatopsis orientalis, the use of the cloned gene to express and purify the encoded enzyme, and a method of using the cloned enzyme in the production of glycopeptide compounds.
The use of antibiotic compounds has had a profound impact on the practice of medicine in the United States and around the world. Two highly effective antibiotic compounds of the glycopeptide class, vancomycin and teichoplanin, have been approved for use in humans.




The glycopeptide antibiotics comprise natural and semi-synthetic compounds of highly functionalized linear heptapeptides having a core structure composed of either seven modified or unusual aromatic amino acids, or a mix of aromatic and aliphatic amino acids. Natural glycopeptide compounds have been found in a variety of bacterial genera including Streptomyces, Actinoplanes, Nocardia, Amycolatopsis, Kibdelosporangia, and Pseudonocardia. M. Zmijewski and J. Fayerman. “Glycopeptide Antibiotics,” In Genetics and Biochemistry of Antibiotic Production, Chap. 18. Ed. L. C. Vining and C. Studtard. Publ. Butterworth Heinemann, Boston (1995). Generally, glycopeptide compounds are differentiated by the placement of sugar substituents on the peptide core. In some instances differentiation arises from the positioning of fatty acid moieties on said sugar substituents. Research has shown that the sugar moieties attached to the core may have an effect on the biological activity of glycopeptide molecules.
At present, investigations into glycosylation of glycopeptides and glycopeptide cores are limited to preliminary observations on crude cellular extracts of bacterial strains that produce glycopeptide compounds. These experiments have demonstrated that the glycosylation reaction appears to involve one or more enzymatic activities which attach sugar residues onto a glycopeptide core. One study, for example, demonstrated a glycosylating activity in a crude cellular extract of a vancomycin-producing strain of Amycolatopsis orientalis. M. Zmijewski & B. Briggs.“Biosynthesis of vancomycin: identification of TDP-glucose:aglycosylvancomycin glucosyltransferase from Amycolatopsis orientalis” FEMS Microbiol. Lett. 59, 129-134 (1989).
The glycosylation of glycopeptide compounds, intrinsically interesting from a scientific point of view, presents a number of practical considerations that warrant continued study of this subject. Recently, a number of glycopeptide resistant strains of pathogenic organisms have been encountered within the clinical environment. This trend toward diminished efficacy of glycopeptide compounds is alarming because of a similar phenomenon in the case of β-lactam antibiotics. It is clear that the rise in antibiotic resistance has occured by a plurality of molecular mechanisms and that resistant organisms possess a diverse repertoire for counteracting the otherwise lethal effect of antibiotic compounds.
In light of the trend toward greater resistance, and in view of the absence of effective alternative treatments, there exists a pressing need to develop new antibiotic compounds. A useful strategy toward this end involves derivitizing presently available glycopeptide compounds by engineering in defined ways the placement and configuration of sugar moieties on the glycopeptide core structure. Achieving molecular rearrangements and substitutions of sugars on glycopeptide compounds by chemical means is difficult if not impossible in most cases. By contrast to chemical procedures, enzymatic methods, if available, would provide an effective means to engineer specific modifications onto the glycopeptide core.
The challenge to provide an enzymatic means for modifying glycopeptides or glycopeptide core molecules has been met by the present invention. Described herein are gtfE genes isolated from Amycolatopsis orientalis which encode glycosyltransferase enzyme GtfE, which adds D-glucose or D-xylose moieties onto the B ring of vancomycin and teichoplanin glyopeptides and core molecules.
BRIEF SUMMARY
The present invention is designed to meet the aforementioned need and provides, inter alia, the isolated gtfE gene and other nucleic acid molecules that encode the GtfE gene product from Amycolatopsis orientalis C329.4. The invention also provides the GtfE protein product of the Amycolatopsis orientalis gtfE gene, in substantially purified form. Both the native Amycolatopsis orientalis gene gtfE, which encodes the activity, as well as a PCR-derived variant thereof, are used to produce proteins which exhibit this activity in a recombinant host cell. The GtfE proteins produced by recombinant methods are useful in the production of novel glycopeptide compounds.
Having the cloned gtfE gene of Amycolatopsis orientalis enables the production of recombinant GtfE protein from which can be made novel derivatives of glycopeptide compounds.
In one embodiment the present invention relates to an isolated DNA molecule encoding GtfE protein, said DNA molecule comprising the nucleotide sequence identified as SEQ ID NO. 1:









ATGCGTGTGT TGTTGTCGAC CTGTGGGAGC CGCGGAGACG TCGAACCACT GGTGGCGTTG
60



 


GCGGTGCGGT TGCGGGAGCG CGGCGCCGAG GTGCGGATGT GCGCGCCGCC GGACTGCGCG
120


 


GATCGGCTGG CCGAAGTCGA CGTGCCGCAT CTGCCCCTCG GTGCGTCGGC GCGCCCGTCG
180


 


GCCGGGCAGG CGAAACCCTT GACGGCCGAG GACATGCTCC GGTTCACGAC CGAGACGATC
240


 


GCCACGCAGT TCGAGCGGAT TCCGGCGGCC GCCGAAGGAT GCGCCGCGGT GGTGACGACC
300


 


GGCCTGCTGG CCGCCGCCAT CGGCGTGCGG TCGGTGGCCG AAAAGCTGGG CATCCCCTAC
360


 


TTCTATGGCT TCCACTGCCC GAGCTATGTG CCGTCGCCGT ACTATGCGCC TCCGCCGCCC
420


 


CTCGGCGAGC CGCCCGCACC GGACGGGACC GACATCCAGG CGCTGTGGGA GCGCAACAAC
480


 


CAGAGCGCCT ACCGGCGGTA CGGGGAGCCG CTCAACAGCA GGCGCGCCGC CATCGGCCTG
540


 


CCGCCGGTGG AGGACATCTT CGGCCACGGC TACACCGATC ACCCGTGGAT GGCGGCGGAC
600


 


CCGGTACTGG CCCCGCTGCA ACCCACGGAT CTCGACGCCG TGCAGACCGG GGCGTGGATC
660


 


CTGCCCGACG AACGACCGAT TTCCGCTGAG CTGGAGGCGT TCCTGGACGC CGGCGCACCA
720


 


CCGGTGTACC TGGGGTTCGG CAGCCTTCGC GCCCCCGCCG ACGCCGCGAA GGTGGCCATC
780


 


GAGGCGATCC GTGCCCACGG CCACCGGGTG ATCCTCTCCC GCGGCTGGGC CGATCTGGTC
840


 


CTGCCCGACG ACCGGGAGGA CTGTTTCGCC ATCGGCGAAG TGAATCAGCA GGTGCTGTTC
900


 


CGCCGGGTGG CCGCCGTCAT CCACCACGGC GGCGCGGGCA CGACCCACGT GGCCACGCGG
960


 


GCGGGCGTCC CCCAGATCCT GGTTCCCCAG ATCGCGGACC AGCCCTACTA CGCCGCCCGG
1020


 


GTGGCCGAAC TGGGGGTCGG TGTGGCGCAT GACGGCCCGA CCCCGACCTT CGACACGTTG
1080


 


TCGGCGGCGC TCACCAAGGC CCTCGCTCCG GAAACGCGCG TGCGAGCGGA AGCCGTGGCG
1140


 


GAAACGGTCC AGACGGACGG GGCCGCGGTG GCCGCGGACC TGTTGTTCGC CGCGGTGACC
1200


 


GGGAACCAGC CCGCCGTTCC CGCC
1224






In another embodiment the present invention relates to a Glycosyltransferase protein molecule, encoded by SEQ ID NO:1 wherein said Glycosyltransferase protein molecule comprises the sequence identified as SEQ ID NO. 2.
In a further embodiment the present invention relates to a ribonucleic acid molecule encoding GtfE protein, said ribonucleic acid molecule comprising the sequence identified as SEQ ID NO. 3:
In yet another embodiment, the present invention relates to a recombinant DNA vector which incorporates the Amycolatopsis orientalis gtfE gene in operable linkage to gene expression sequences enabling the gtfE gene to be transcribed and translated in a host cell.
In still another embodiment the present invention relates to homologous or heterologous host cells which have been transformed or transfected with the cloned gtfE gene of Amycolatopsis orientalis such that the gtfE gene is expressed in the host cell.
In still another embodiment, the present invention relates to a method for producing glycopeptide compounds wherein GtfE protein produced by recombinant cells is utilized to add one or more sugar moieties onto a glycopeptide or glycopeptide core, in vitro or in vivo.
In yet another embodiment, the present invention relates to novel glycopeptide compounds.



DESCRIPTION OF THE DRAWINGS
FIG. 1. Plasmid pCZA338, which is useful for high level expression of the Amycolatopsis orientalis GtfEp enzyme activity in heterologous or homologous procaryotic host cells.
FIG. 2. Plasmid pCZA345, which may be used to express the Amycolatopsis orientalis GtfEp enzyme activity in heterologous host Streptomyces toyocaensis. 



DEFINITIONS
“AGV,” which denotes aglycosylvancomycin, comprises a vancomycin core having a free hydroxl group on the B ring in place of the disaccharide moiety.
“A47934” and “A41030A” refer to glycopeptide compounds, comprising a teichoplanin core, and naturally lacking a sugar moiety. A47934 is produced in Streptomyces toyocaensis; A41030A is produced in Streptomyces virginiae. 
“gtfE” refers to the native genomic sequence which encodes glucosyltransferase enzyme activity in Amycolatopsis orientalis. This sequence is identified as SEQ ID NO.1.
“gtfEp” refers to a PCR-derived variant of gtfE having two base pair changes in SEQ ID NO.1, at position 1003, where a “T” residue is inserted in place of a “C” residue, and at position 1179 where a “H” residue is inserted in place of a “C” residue. This variant was produced during a PCR reaction. It also encodes an active glucosyltransferase enzyme activity.
“GtfE” refers to the glucosyltransferase encoded by gtfE and identified as SEQ ID NO.2.
“GtfEp” refers to the glucosyltransferase encoded by gtfEp, the PCR variant, wherein a single amino acid substitution occurs in SEQ ID NO.2, at position 335, where Ser replaces Pro. GtfE and GtfEp exhibit glucosyltransferase enzyme activity.
The terms “cleavage” or “restriction” of DNA refers to the catalytic cleavage of the DNA with a restriction enzyme that acts only at certain sequences in the DNA (viz. sequence-specific endonucleases). The various restriction enzymes used herein are commercially available and their reaction conditions, cofactors, and other requirements are used in the manner well known to one of ordinary skill in the art. Appropriate buffers and substrate amounts for particular restriction enzymes are specified by the manufacturer or can readily be found in the literature.
The term “fusion protein” denotes a hybrid protein molecule not found in nature comprising a translational fusion or enzymatic fusion in which two or more different proteins or fragments thereof are covalently linked on a single polypeptide chain.
The term “plasmid” refers to an extrachromosomal genetic element. The starting plasmids herein are either commercially available, publicly available on an unrestricted basis, or can be constructed from available plasmids in accordance with published procedures. In addition, equivalent plasmids to those described are known in the art and will be apparent to the ordinarily skilled artisan.
“Recombinant DNA cloning vector” as used herein refers to any autonomously replicating agent, including, but not limited to, plasmids and phages, comprising a DNA molecule to which one or more additional DNA segments can or have been added.
The term “recombinant DNA expression vector” as used herein refers to any recombinant DNA cloning vector, for example a plasmid or phage, in which a promoter and other regulatory elements are present to enable transcription of the inserted DNA.
The term “vector” as used herein refers to a nucleic acid compound used for introducing exogenous DNA into host cells. A vector comprises a nucleotide sequence which may encode one or more protein molecules. Plasmids, cosmids, viruses, and bacteriophages, in the natural state or which have undergone recombinant engineering, are examples of commonly used vectors.
The terms “complementary” or “complementarity” as used herein refers to the capacity of purine and pyrimidine nucleotides to associate through hydrogen bonding in double stranded nucleic acid molecules. The following base pairs are complementary: guanine and cytosine; adenine and thymine; and adenine and uracil.
“Exconjugant” refers to Actinomycetes or other cell type which has incorporated a cloning vector, or other DNA, or recombinant DNA molecule following conjugal transfer from E. coli. 
The term “glycopeptide” refers to a functionalized linear heptapeptide compound of natural or semi-synthetic origin, said compound having a core structure.
“Glycopeptide core” or “core” or “core compound” interchangeably denote the progenitor structure of all glycopeptide compounds, comprising either 7 modified or unusual aromatic amino acids or a mix or aromatic and aliphatic amino acids.
“Glycosylating substrate” refers to a compound which functions as a donor of a sugar moiety in an enzymatic glycosylation reaction, for example, uridine diphosphate-D-glucose.
“Glucosyltransferase” means GtfE or GtfEp, or functional equivalent thereof.
“Isolated nucleic acid compound” refers to any RNA or DNA sequence, however constructed or synthesized, which is locationally distinct from its natural location.
A “primer” is a nucleic acid fragment which functions as an initiating substrate for enzymatic or synthetic elongation of, for example, a nucleic acid molecule.
The term “promoter” refers to a DNA sequence which directs transcription of DNA to RNA.
A “probe” as used herein is a labeled nucleic acid compound which hybridizes with another nucleic acid compound.
The term “hybridization” as used herein refers to a process in which two or more strands of nucleic acid join through base pairing with complementary strands. “Selective hybridization” refers to hybridization under conditions of high stringency. The degree of hybridization between nucleic acid molecules varies with the degree of complementarity, the stringency of the hybridization conditions, and the length of the strands.
The term “stringency” refers to a set of hybridization conditions, for example temperature and salt concentration, which may be varied to achieve “high stringency” or “low stringency” conditions, thereby varying the degree of hybridization of one nucleic acid molecule with another nucleic acid molecule. High stringency conditions disfavor non-homologous basepairing.
DETAILED DESCRIPTION
The gtfE gene of Amycolatopsis orientalis encodes a glycosylating enzyme, GtfE. The enzyme will add D-glucose or D-xylose onto the free hydroxl group of the B ring of aglycosylvancomycin (AGV), producing desvancosaminylvancomycin (DVV), or the xylose derivative thereof. The enzyme uses TDP-glucose, UDP-glucose, or UDP-xylose as the glycosylating substrate. The cloned GtfE enzyme will also add D-glucose onto teichoplanin cores such as A47934 and A41030. (see Table).









TABLE









Glycopeptide












Glycosylating Substrate
AGV
A41036
A47934







No sugar
−
−
−



TDP-glucose
+
+
+



UDP-glucose
+
+
+



UDP-galactose
−



UDP-mannose
−



UDP-xylose
+



UDP-N-acetylglucosamine
−



UDP-galactouronic acid
−










The gtfE gene of Amycolatopsis orientalis comprises a DNA sequence of 1224 nucleotide base pairs (SEQ ID NO. 1). There are no intervening sequences. Those skilled in the art will recognize that owing to the degeneracy of the genetic code (i.e. 64 codons which encode 20 amino acids), numerous “silent” substitutions of nucleotide base pairs could be introduced into the sequence identified as SEQ ID NO. 1 without altering the identity of the encoded amino acid(s) or protein product identified as SEQ ID NO:2. All such substitutions are intended to be within the scope of the invention. Moreover, skilled artisans will recognize that many amino acid substitutions may be made without altering the activity or function of a protein. All such substitutions are intended to be within the scope of this invention. For example, one specific variant of gtfE was isolated during a PCR. This variant, termed gtfEp, introduces two base pair changes in SEQ ID NO.1 resulting in one amino acid change in SEQ ID NO.2 (See Definitions). The gtfEp variant and the protein it encodes, GtfEp, encode a functional glucosyltransferase activity.
Gene Isolation Procedures
Those skilled in the art will recogize that the GtfE gene may be obtained by a plurality of applicable techniques including, for example, polymerase chain reaction (PCR) amplification, or de novo DNA synthesis. (See e.g., J. Sambrook et al. Molecular Cloning, 2d Ed. Chap. 14 (1989)).
Methods for constructing gene libraries in a suitable vector such as a plasmid or phage for propagation in procaryotic or eucaryotic cells are well known to those skilled in the art. [See e.g. J. Sambrook et al. Supra]. Suitable cloning vectors are widely available.
Skilled artisans will recognize that the gtfE gene of Amycolatopsis orientalis or fragment thereof could also be isolated by PCR amplification of Amycolatopsis orientalis genomic DNA using oligonucleotide primers targeted to any suitable region of SEQ ID NO. 1. Methods for PCR amplification are widely known in the art. See e.g. PCR Protocols: A Guide to Method and Application, Ed. M. Innis et al., Academic Press (1990), which hereby is incorporated by reference. The PCR amplification, which comprises genomic DNA, suitable enzymes, primers, and buffers, is conveniently carried out in a DNA Thermal Cycler (Perkin Elmer Cetus, Norwalk, Conn.). A positive PCR amplification is determined by detecting an appropriately-sized DNA fragment following agarose gel electrophoresis.
The gtfE gene, which comprises nucleic acid encoding SEQ ID NO:2, may also be produced using synthetic methodology. The synthesis of nucleic acids is well known in the art. See, e.g., E. L. Brown, R. Belagaje, M. J. Ryan, and H. G. Khorana, Methods in Enzymology, 68:109-151 (1979). The DNA segments corresponding to the gtfE gene could be generated using a conventional DNA synthesizing apparatus, such as the Applied Biosystems Model 380A or 380B DNA synthesizers (Applied Biosystems, Inc., 850 Lincoln Center Drive, Foster City, Calif. 94404) which employ phosphoramidite chemistry. Alternatively, phosphotriester chemistry may be employed to synthesize the nucleic acids of this invention. [See, e.g., M. J. Gait, ed., Oligonucleotide Synthesis, A Practical Approach, (1984).]
The ribonucleic acids of the present invention may be prepared using the polynucleotide synthetic methods discussed supra, or they may be prepared enzymatically using RNA polymerases to transcribe a DNA template.
The most preferred systems for preparing the ribonucleic acids of the present invention employ the RNA polymerase from the bacteriophage T7 or the bacteriophage SP6. These RNA polymerases are highly specific and require the insertion of bacteriophage-specific sequences at the 5′ end of the template to be transcribed. See, J. Sambrook, et al., supra, at 18.82-18.84.
This invention also provides nucleic acids, RNA or DNA, which are complementary to SEQ ID NO:1 or SEQ ID NO:3.
The present invention also provides probes and primers useful for a variety of molecular biology techniques. For example, the nucleic acid compounds of the present invention may be used to hybridize to genomic DNA which has been digested with one or more restriction enzymes and separated on an electrophoretic gel. The hybridization of radiolabeled probes onto such restricted DNA, usually fixed to a membrane after electrophoresis, is well known in the art. See, e.g., J. Sambrook, supra. A compound which comprises SEQ ID NO:1, SEQ ID NO:3 or a complementary sequence of SEQ ID No:1 or SEQ ID NO:3, or a fragment thereof, and which is at least 18 base pairs in length, and which will selectively hybridize to Amycolatopsis orientalis DNA or mRNA encoding gtfE, is provided. Preferably, the 15 or more base pair compound is DNA. The probes and primers of this invention can be prepared by techniques well known to those skilled in the art (See e.g. Sambrook et al. supra). In a most preferred embodiment these probes and primers are synthesized using chemical means as described above.
Another aspect of the present invention relates to recombinant DNA cloning vectors and expression vectors comprising the nucleic acids of the present invention. Many of the vectors encompassed within this invention are described above. The preferred nucleic acid vectors are those which comprise DNA. The most preferred recombinant DNA vectors comprise the isolated DNA sequence, SEQ ID NO:1.
Choosing the most appropriate cloning vector or expression vector depends upon a number of factors including the availability of appropriate restriction enzyme sites, the type of host cell into which the vector is to be transfected or transformed, the purpose of the transfection or transformation (e.g., stable transformation as an extrachromosomal element, or integration into the host chromosome), the presence or absence of readily assayable or selectable markers (e.g., antibiotic resistance markers and metabolic markers), and the desired number of copies of the gene to be present in the host cell.
Vectors suitable to carry the nucleic acids of the present invention comprise RNA viruses, DNA viruses, lytic bacteriophages, lysogenic bacteriophages, stable bacteriophages, plasmids, viroids, and the like. The most preferred vectors are plasmids.
When preparing an expression vector the skilled artisan understands that there are many variables to be considered, for example, whether to use a constitutive or inducible promoter. Inducible promoters are preferred because they enable high level, regulatable expression of an operably linked gene. A number of inducible promoters responding to a variety of induction signals are available, for example, carbon source, metal ions, and heat. The practitioner also understands that the amount of nucleic acid or protein to be produced dictates, in part, the selection of the expression system. The addition of certain nucleotide sequences, such as a sequence encoding a signal peptide preceding the coding sequence, is useful to direct localization of the resulting polypeptide.
Host cells harboring the nucleic acids disclosed herein are also provided by the present invention. A preferred host is E. coli which has been transfected or transformed with a vector which comprises a nucleic acid of the present invention. Another preferred host is Streptomyces toyocaensis. 
The present invention also provides a method for constructing a recombinant host cell capable of expressing SEQ ID NO:2, said method comprising transforming or otherwise introducing into a host cell a recombinant DNA vector that comprises an isolated DNA sequence which encodes SEQ ID NO:2. A preferred host cell is any strain of E. coli which can accomodate high level expression of a gene(s) introduced by transformation or transfection. Preferred vectors for expression are those which comprise SEQ ID NO:1. Transformed host cells may be cultured under conditions well known to skilled artisans such that SEQ ID NO:2 is expressed, thereby producing GtfE protein in the recombinant host cell.
Protein Production Methods
One embodiment of the present invention relates to the substantially purified protein GtfE identified as SEQ ID NO:2 and encoded by the gtfE gene or functionally related proteins of Amycolatopsis orientalis. 
Skilled artisans will recognize that the proteins of the present invention can be synthesized or purified by any number of suitable methods. For example, the amino acid compounds of the invention can be made by chemical methods well known in the art, including solid phase peptide synthesis or recombinant methods. Both methods are described in U.S. Pat. No. 4,617,149, incorporated herein by reference.
The principles of solid phase chemical synthesis of polypeptides are well known in the art and are described in a number of general texts on the subject. See, e.g., H. Dugas and C. Penney, Bioorganic Chemistry (1981) Springer-Verlag, New York, 54-92. For example, peptides may be synthesized by solid-phase methodology using an Applied Biosystems 430A peptide synthesizer (Applied Biosystems, Foster City, Calif.) and synthesis cycles supplied by Applied Biosystems. Protected amino acids, such as t-butoxycarbonyl-protected amino acids, and other reagents are commercially available from many chemical supply houses.
Sequential t-butoxycarbonyl chemistry using double- couple protocols are applied to the starting p-methyl benzhydryl amine resins for the production of C-terminal carboxamides. For the production of C-terminal acids, the corresponding pyridine-2-aldoxime methiodide resin is used. Asparagine, glutamine, and arginine are coupled using preformed hydroxy benzotriazole esters. Following completion of the synthesis the peptides may be deprotected and cleaved from the resin with anhydrous hydrogen fluoride containing 10% meta-cresol. Cleavage of the side chain protecting group(s) and of the peptide from the resin is carried out at zero degrees Celcius or below, preferably −20° C. for thirty minutes followed by thirty minutes at 0° C.
The proteins of the present invention can also be produced by recombinant DNA methods using the cloned gtfE gene of Amycolatopsis orientalis. Recombinant methods are preferred if a high yield is desired. Expression of the cloned gtfE gene can be carried out in a variety of suitable host cells well known to those skilled in the art. The gtfE gene is introduced into a host cell by any suitable transformation, transfection, or conjugation means, well known to those skilled in the art. While chromosomal integration of the cloned gtfE gene is within the scope of the present invention, it is preferred that the gene be cloned into a suitable extra-chromosomally maintained expression vector in which the coding region of the gtfE gene is operably linked to a constitutive or inducible promoter.
The basic steps in the recombinant production of the GtfE protein are:

    
    
        a) constructing a natural, synthetic or semi-synthetic DNA encoding GtfE protein;
        b) integrating said DNA into an expression vector in a manner suitable for expressing the GtfE protein, either alone or as a fusion protein;
        c) transforming, transfecting, or otherwise introducting said expression vector into an appropriate eukaryotic or prokaryotic host cell to form a recombinant host cell,
        d) culturing said recombinant host cell under conditions that favor expression of the GtfE protein; and
        e) recovering and purifying the GtfE protein by any suitable means.

Expressing Recombinant GtfE Protein in Procaryotic and Eucaryotic Host Cells

    
    


In general, prokaryotes are used for cloning DNA and for constructing the vectors of the present invention. Prokaryotes are also employed in the production of the GtfE protein. For example, the Escherichia coli K12 strain 294 (ATCC No. 31446) is particularly useful for the expression of foreign proteins. Other strains of E. coli, bacilli such as Bacillus subtilis, enterobacteriaceae such as Salmonella typhimurium or Serratia marcescans, various Pseudomonas species, and other bacteria, such as Streptomyces, may also be employed as host cells in the cloning and expression of the recombinant proteins of this invention.
Promoters suitable for driving the expression of gene sequences in prokaryotes include β-lactamase [e.g. vector pGX2907, ATCC 39344, contains a replicon and β-lactamase gene], lactose systems [Chang et al., Nature (London), 275:615 (1978); Goeddel et al., Nature (London), 281:544 (1979)], alkaline phosphatase, and the tryptophan (trp) promoter system [vector pATH1 (ATCC 37695) which is designed to facilitate expression of an open reading frame as a trpE fusion protein under the control of the trp promoter]. Hybrid promoters such as the tac promoter (isolatable from plasmid pDR540, ATCC-37282) are also suitable. Still other bacterial promoters, whose nucleotide sequences are generally known, enable one of skill in the art to ligate such promoter sequences to DNA encoding the proteins of the instant invention using linkers or adapters to supply any required restriction sites. Promoters for use in bacterial systems also will contain a Shine-Dalgarno sequence operably linked to the DNA encoding the desired polypeptides. These examples are illustrative rather than limiting.
The protein of this invention may be synthesized by recombinant or chemical means as the amino acid sequence identified as SEQ ID NO:2, or as a fusion protein comprising the protein of interest and another protein or peptide which may be removable by enzymatic or chemical cleavage. Expression as a fusion protein may prolong the lifespan, increase the yield of the desired peptide, or provide a convenient means for purifying the protein. A variety of peptidases (e.g. enterokinase and thrombin) which cleave a polypeptide at specific sites are known. Furthermore, particular chemicals (e.g. cyanogen bromide) will cleave a polypeptide chain at specific sites. The skilled artisan will appreciate the modifications necessary to the amino acid sequence (and synthetic or semi-synthetic coding sequence if recombinant means are employed) to incorporate site-specific internal cleavage sites. See e.g., P. Carter, “Site Specific Proteolysis of Fusion Proteins”, Chapter 13, in Protein Purification: From Molecular Mechanisms to Large Scale Processes, American Chemical Society, Washington, D.C. (1990).
In addition to prokaryotes, mammalian host cells and eukaryotic microbes such as yeast may also be used to isolate and express the genes of the present invention. The simple eucaryote Saccharomyces cerevisiae, is the most commonly used eukaryotic microorganism, although a number of other yeasts such as Kluyveromyces lactis are also suitable. For expression in Saccharomyces, the plasmid YRp7 (ATCC-40053), for example, may be used. See, e.g., L. Stinchcomb, et al., Nature, 282:39 (1979); J. Kingsman et al., Gene, 7:141 (1979); S. Tschemper et al., Gene, 10:157 (1980). Plasmid YRp7 contains the TRP1 gene which provides a selectable marker for use in a trp1 auxotrophic mutant.
Purification of GtfE Protein Produced in Recombinant Host
The recombinantly produced protein may be purified from cellular extracts of transformed cells by any suitable means. In a preferred protein purification method, the gtfE gene is modified at the 5′ end to incorporate several histidine residues at the amino terminus of the GtfE protein product. The “histidine tag” enables a single-step protein purification method referred to as “immobilized metal ion affinity chromatography” (IMAC), essentially as described in M. C. Smith et al. “Chelating Peptide-immobilized metal-ion affinity chromatography,” Chapter 12, in Protein Purification: From Molecular Mechanisms to Large Scale Processes, American Chemical Society, Washington, D.C. (1990), and in U.S. Pat. No. 4,569,794 both of which hereby are incorporated by reference. The IMAC method enables rapid isolation of substantially pure protein.
Synthesis of Glycopeptide Compounds Using a Cloned Enzyme
The cloned GtfE enzyme is useful for developing new glycopeptide compounds by, for example, glycosylating already existing glycopeptide compounds and cores in vivo or in vitro. A method embodied herein comprises glycosylating a glycopeptide or glycopeptide core compound, by contacting the glycopeptide with the cloned GtfE protein and monitoring the glycopeptide compound that is produced.
The instant invention provides an enzymatic method for glycosylating vancomycin and teichoplanin core compounds using the cloned A. orientalis gtfE gene, said method comprising the steps of:

    
    
        a) expressing the cloned gtfE gene in a host cell so that GtfE enzyme is produced;
        b) exposing said GtfE enzyme to a glycopeptide or core compound, in vivo or in vitro;
        c) providing a suitable glycosylating substrate; and
        d) characterizing and/or purifying the product glycopeptide by any suitable means.
    
    


An expression vector carrying the cloned gtfE gene of Amycolatopsis orientalis is transformed, transfected, or introduced by conjugation into a suitable host cell using standard methods. Suitable conjugation methods are described in P. Matsushima and R. H. Baltz, “A gene cloning system for Streptomyces toyocaensis” Microbiol. 142, 261-267 (1996), which hereby is incorporated by reference. Cells which contain the vector are propagated under conditions suitable for expression of the Glycosyltransferase protein. If the gtfE gene is under the control of an inducible promoter, growth media and other conditions should incorporate the appropriate inducer.
The instant method can be used to enzymatically attach sugar residues to glycopeptide or glycopeptide cores such as, for example, members of the vancomycin and teichoplanin core structures. The method will, for example, attach a D-glucose or D-xylose moiety at the free hydroxyl group of the B ring of aglycosylvancomycin. The method can also be used to glucosylate teichoplanin cores that naturally lack sugar residues, such as, for example, compounds A41030A and A47934 (See e.g. M. Zmijewski and J. Fayerman. “Glycopeptide Antibiotics,” In Genetics and Biochemistry of Antibiotic Production, Chap. 18. Ed. L. C. Vining and C. Studtard. Publ. Butterworth Heinemann, Boston (1995)).
The method can be adapted to substantially purified recombinant GtfE protein, as described herein, or to a crude cellular extract isolated from a recombinant cell culture that expresses the GtfE protein by virtue of having been transformed, transfected, or conjugated with the Amycolatopsis orientalis gtfE gene.
The invention also comprises in vivo glycosylation reactions in which the cloned A. orientalis gtfE gene is introduced into a glycopeptide-producing bacterial strain such that under suitable growth conditions the glycopeptide compound, which is indigenous to the strain, is specifically glycosylated intracellularly. For example, the gtfE gene may be introduced into an A47934-producing strain of S. toyocaensis such that compound A47934, which naturally lacks a sugar moiety, is glucosylated at the free hydroxl group of the B ring. The preferred method for introducing the gtfE gene into S. toyocaensis is by conjugation with an E. coli strain which carries the gtfE gene on a suitable recombinant plasmid.
The following examples more fully describe the present invention. Those skilled in the art will recognize that the particular reagents, equipment, and procedures described are merely illustrative and are not intended to limit the present invention in any manner.
EXAMPLE 1
Construction of a DNA Vector Containing the gtfE Gene
A gtfE gene cassette may be conveniently generated from A. orientalis genomic DNA by PCR. Suitable oligonucleotide primers are synthesized to contain appropriate cloning sites and regions complementary to the terminal region of SEQ ID NO.1. The amplified DNA which comprises the gtfE gene cassette is then ligated into any suitable vector, for example, PET11A (Novogen, Madison, Wis.).
EXAMPLE 2 
Construction of a DNA Vector Containing gtfEp Gene
A gtfEp gene cassette may be conveniently made by any suitable site-directed mutagenesis procedure. A suitable commercially available kit, “MORPH,” utilizes a DpnI hemimethylation procedure (available from 5 Prime 3 Prime, Inc. Boulder, Colo. 80303).
Briefly, a plasmid carrying the wild-type sequence, gtfE, is prepared from any dam+ E. coli, such as DH5α, HB101, RR1, and JM101. The purified target DNA is then denatured at 100° C. and annealed to an oligonucleotide which carries the desired mutation. In this case, a “T” is inserted in place of a “C” at position 1003 of SEQ ID NO.1. The oligonucleotide is extended with T4 DNA polymerase to generate hemi-methylated, double-stranded DNA molecules resistant to digestion by DpnI endonuclease. Following transformation into a mutS bacterial strain colonies which carry the mutated gene may be identified by any suitable means well known to those skilled in the art. A second round of mutagenesis can be carried out in order to introduce a “T” in place of a “C” at position 1179 of SEQ ID NO.1. The desired cassette can then be inserted into a suitable vector by any suitable means.
EXAMPLE 3 
Construction of a DNA Vector Which Expresses in Escherichia coli a Glycosylase Activity Encoded By a Glucosyltranserase Gene of Amycolatopsis orientalis 
Plasmid pCZA338 (see FIG. 1) is an approximately 7 kilobasepair expression vector suitable for expressing the gtfEp gene at high levels in a procaryotic host, for example E. coli. Plasmid pCZA338 was derived from parent plasmid PET-11a (obtained from Novagen, Madison, Wis.), which contains an origin of DNA replication (ori), an ampicillin resistance gene (Amp), the T7 promoter region, and the laci gene for repressing the lac operon.
The gtfEp gene cassette inserted into pCZA338 was generated by the PCR carried out on genomic DNA isolated from A. orientalis strain C329.4 (NRRL accession #2452) using standard conditions. Primers used in the amplification reaction were complementary to the 5′ and 3′ ends of the gtfE gene sequence specified in SEQ ID NO: 1 and were engineered to contain NdeI and Bgl II restriction sites. The PCR-amplified gtfEp gene sequence was digested with NdeI and Bgl II and ligated into pET11a, which had been digested with NdeI and BamHI.
The gtfEp gene cassette in pCZA338 encodes a single amino acid substitution in SEQ ID NO.2 wherein a Pro at position 335 is replaced by a Ser at position 335. The protein encoded by gtfEp, designated GtfEp, retains glycosyltransferase enzyme activity.
EXAMPLE 4 
Construction of a Vector for Expressing the Amycolatopsis orientalis Glucosyltransferase Activity in Streptomyces toyocaensis 
Plasmid pCZA338 (see Example 3) was digested with XbaI and HindIII and an approximately 1.5 Kb DNA fragment carrying the gene was isolated by agarose gel electrophoresis and ligated into XbaI and HindIII-digested pIJ4070. pIJ4070 is a derivative of pIJ2926 [Jannsen, G. et al. Gene 124, 133 (1993)] in which the ermEp promoter (functional in S. toyocaensis), carried on a KpnI to BamHI fragment, has a 3 bp deletion in the −35 region [Schmitt-John and Engels, Appl. Microbiol. Biotechnol. 36, 493 (1992)]. The plasmid resulting from the ligation of said gene cassette and pIJ4070, designated pCZA340, was digested. with Bgl II and an approximately 1.8 Kb fragment which contained the ermEp promoter and the gene sequence encoding glycosyltransferase activity, was ligated into appropriately restricted pSET152 [Bierman, M. et al. Gene, 116, 43 (1992)]. The resulting plasmid, pCZA345, is approximately 7 kilobase pair and will transform E. coli efficiently. Plasmid pCZA345 also enables expression of A. orientalis glycosyltransferase activity in S. toyocaensis following conjugation with an E. coli cell harboring plasmid pCZA345.
EXAMPLE 5 
Transformation of Escherichia coli With an Expression Plasmid Which Encodes a Glycosyltransferase Activity Derived from Amycolatopsis orientalis 
Plasmid pCZA338 was transformed into E. coli BL21(DE3) (hsdS gal λcIts857 ind1Sam7nin5lacUV5-T7gene 1) using standard methods (See e.g. Sambrook et al. Supra).
EXAMPLE 6 
Introduction of Plasmid pCZA345 Into S. toyocaensis by Conjugation
Plasmid pCZA345 was transformed by standard methods into E. coli strain S17-1. For conjugation from E. coli to Streptomyces toyocaensis about 100 μl of a spore stock comprising S. toyocaensis A80934 ( ̃4×108/ml) was mixed with 50 μl stationary phase S17-1 containing pCZA345 and spread onto the surface of modified R2 agar. The agar plates were incubated for 16-24 hours at 29° C., then apramycin plus naladixic acid in 3 ml soft nutrient agar was added to the surface of each plate to give a final bottom agar concentration of 25 μg/ml for each antibiotic. The plates were incubated for 5 to 10 days and apramycin resistant exconjugants were counted.
EXAMPLE 7 
In Vitro Glycosylation of Desyancosaminyl Vannomycin Using Cloned Gene from Amycolatopsis orientalis 
Approximately 25 ml of a culture of E. coli BL21(DE3) cells transformed with plasmid pCZA338 were grown to an OD600 of about 0.6. Induction of gene expression was effected by adding 1 mM IPTG with shaking at room temperature for 2 to 3 hours. Thereafter, cells from about 20 ml of the induced culture were pelleted by centrifugation and resuspended in 2 ml of 50 mM Tris pH 9.0, 100 μg/ml lysozyme with incubation on ice for 10 minutes to effect cell lysis. After cell lysis the suspension was passed through a 23-gauge syringe and centrifuged at 10,000×g for 15 minutes to pellet cell debris. The resulting cell extract was used for the glycosylation reaction.
The 1 ml glycosylation reaction contained:


    
    
        1 mg AGV in 50 mM Tris HCl, pH 9.0
        5 mg TDP-glucose
        1 mg bovine serum albumin (BSA)
        20 μl 1 M MgCl2 
        20 μl 1 M CaCl2 
        5 μl 1 M dithiothreitol (DTT)
        445 μl cell extract
        Distilled water to 1 ml.

A control reaction contained cell extract from non-transformed BL21 (DE3). After incubation overnight at 37° C. with slight shaking the reaction was filtered through a 0.45 micron filter and analyzed by HPLC. The test sample but not the control showed a new peak appearing at about 10 minutes retention time. The new peak was found by mass spectrometry to possess the mass expected of desvancosaminyl vancomycin. (Data not shown).

    
    


EXAMPLE 8 
In Vivo Glycosylation of a Glycopeptide in Streptomayces toyocaensis Using Cloned Amycolatopsis orientalis Glycosyltransferase Gene
Recombinant S. toyocaensis A80934 carrying plasmid pCZA345 (prepared as described in Example 6) was fermented on a glucose containing medium for 7 days at 30° C. The fermentation medium contained (per liter): glucose—15 g; potato dextrin—30 g; blackstrap molasses—3 g; nutrisoy flour—15 g; casein—5 g; CaCO3—5 g, at pH 6.8-7.0. After fermentation the cells were extracted and the glycopeptide constituents analyzed by HPLC, as described in Zmijewski et al. Antimicrob. Agents. Chemother. 31, 1497-1501 (1987). The HPLC analysis revealed a new peak which was absent in the untransformed control.
EXAMPLE 9 
Bioactivity of a Glycosylated A47934 Produced In Vivo In Streptococcus toyocaensis 
The glycosylated A47934 produced in Example 8 was purified by preparative HPLC methodology from crude cellular extracts of exconjugants using a Waters C18 Nova-Pak column (40×300 mm) and UV detection at 280 nm. Elution was accomplished with a linear gradient of 5% CH3CN-95% buffer to 80% CH3CN-20% buffer over 30 minutes. The buffer used was 0.5% triethylamine in water, adjusted to pH 3 with H3PO4. The desired fractions were subsequently desalted with a Waters C18 Sep-Pak (35 cc) and lyophilized.
The HPLC-purified glycosylated A47934 was demonstrated to have antibacterial activity when tested by a standard plate assay.

## Claims

1. A glycopeptide having the formula (I):

2. A glycopeptide having the formula (II):