The Diiron Monooxygenase CmlA from Chloramphenicol Biosynthesis Allows Reconstitution of β-Hydroxylation during Glycopeptide Antibiotic Biosynthesis

β-Hydroxylation plays an important role in the nonribosomal peptide biosynthesis of many important natural products, including bleomycin, chloramphenicol, and the glycopeptide antibiotics (GPAs). Various oxidative enzymes have been implicated in such a process, with the mechanism of incorporation varying from installation of hydroxyl groups in amino acid precursors prior to adenylation to direct amino acid oxidation during peptide assembly. In this work, we demonstrate the in vitro utility and scope of the unusual nonheme diiron monooxygenase CmlA from chloramphenicol biosynthesis for the β-hydroxylation of a diverse range of carrier protein bound substrates by adapting this enzyme as a non-native trans-acting enzyme within NRPS-mediated GPA biosynthesis. The results from our study show that CmlA has a broad substrate specificity for modified phenylalanine/tyrosine residues as substrates and can be used in a practical strategy to functionally cross complement compatible NRPS biosynthesis pathways in vitro.

F-O-G Ring Formation in Glycopeptide Antibiotic Biosynthesis is Catalysed by OxyE

The glycopeptide antibiotics are peptide-based natural products with impressive antibiotic function that derives from their unique three-dimensional structure. Biosynthesis of the glycopeptide antibiotics centres of the combination of peptide synthesis, mediated by a non-ribosomal peptide synthetase, and the crosslinking of aromatic side chains of the peptide, mediated by the action of a cascade of Cytochrome P450s. Here, we report the first example of in vitro activity of OxyE, which catalyses the F-O-G ring formation reaction in teicoplanin biosynthesis. OxyE was found to only act after an initial C-O-D crosslink is installed by OxyB and to require an interaction with the unique NRPS domain from glycopeptide antibiotic - the X-domain - in order to display catalytic activity. We could demonstrate that OxyE displays limited stereoselectivity for the peptide, which mirrors the results from OxyB-catalysed turnover and is in sharp contrast to OxyA. Furthermore, we show that activity of a three-enzyme cascade (OxyB/OxyA/OxyE) in generating tricyclic glycopeptide antibiotic peptides depends upon the order of addition of the OxyA and OxyE enzymes to the reaction. This work demonstrates that complex enzymatic cascades from glycopeptide antibiotic biosynthesis can be reconstituted in vitro and provides new insights into the biosynthesis of these important antibiotics.

The pathway-specific regulatory genes, tei15* and tei16*, are the master switches of teicoplanin production in Actinoplanes teichomyceticus

Pathogenic antibiotic-resistant bacteria are an unprecedented threat to health care worldwide. The range of antibiotics active against these bacteria is narrow; it includes teicoplanin, a "last resort" drug, which is produced by the filamentous actinomycete Actinoplanes teichomyceticus. In this report, we determine the functions of tei15* and tei16*, pathway-specific regulatory genes that code for StrR- and LuxR-type transcriptional factors, respectively. The products of these genes are master switches of teicoplanin biosynthesis, since their inactivation completely abolished antibiotic production. We show that Tei15* positively regulates the transcription of at least 17 genes in the cluster, whereas the targets of Tei16* still remain unknown. Integration of tei15* or tei16* under the control of the aminoglycoside resistance gene aac(3)IV promoter into attBϕC31 site of the A. teichomyceticus chromosome increased teicoplanin productivity to nearly 1 g/L in TM1 industrial medium. The expression of these genes from the moderate copy number episomal vector pKC1139 led to 3-4 g/L teicoplanin, while under the same conditions, wild type produced approximately 100 mg/L. This shows that a significant increase in teicoplanin production can be achieved by a single step of genetic manipulation of the wild-type strain by increasing the expression of the tei regulatory genes. This confirms that natural product yields can be increased using rational engineering once suitable genetic tools have been developed. We propose that this new technology for teicoplanin overproduction might now be transferred to industrial mutants of A. teichomyceticus.

Glycerol affects the acyl moieties of teicoplanin components produced by Actinoplanes teichomyceticus MSl2210

Teicoplanin, a glycopeptide antibiotic, is composed of five main components, denoted T-A2-1 to T-A2-5. We investigated the use of glycerol as a carbon source affecting the teicoplanin components and its acyl moieties. As a result, we show the change of teicoplanin components, as well as an increase of total teicoplanin yields, caused by the addition of glycerol to the production medium. Analysis of the total cell lipids upon the addition of glycerol also showed a corresponding change in the proportion of teicoplanin, suggesting that glycerol strongly affects a change of teicoplanin branched acyl moieties.

Phosphate-controlled regulator for the biosynthesis of the dalbavancin precursor A40926

The actinomycete Nonomuraea sp. strain ATCC 39727 produces the glycopeptide A40926, the precursor of the novel antibiotic dalbavancin. Previous studies have shown that phosphate limitation results in enhanced A40926 production. The A40926 biosynthetic gene (dbv) cluster, which consists of 37 genes, encodes two putative regulators, Dbv3 and Dbv4, as well as the response regulator (Dbv6) and the sensor-kinase (Dbv22) of a putative two-component system. Reverse transcription-PCR (RT-PCR) and real-time RT-PCR analysis revealed that the dbv14-dbv8 and the dbv30-dbv35 operons, as well as dbv4, were negatively influenced by phosphate. Dbv4 shows a putative helix-turn-helix DNA-binding motif and shares sequence similarity with StrR, the transcriptional activator of streptomycin biosynthesis in Streptomyces griseus. Dbv4 was expressed in Escherichia coli as an N-terminal His(6)-tagged protein. The purified protein bound the dbv14 and dbv30 upstream regions but not the region preceding dbv4. Bbr, a Dbv4 ortholog from the gene cluster for the synthesis of the glycopeptide balhimycin, also bound to the dbv14 and dbv30 upstream regions, while Dbv4 bound appropriate regions from the balhimycin cluster. Our results provide new insights into the regulation of glycopeptide antibiotics, indicating that the phosphate-controlled regulator Dbv4 governs two key steps in A40926 biosynthesis: the biosynthesis of the nonproteinogenic amino acid 3,5-dihydroxyphenylglycine and critical tailoring reactions on the heptapeptide backbone.

A two-dimensional electrophoresis and mass spectrometry protein analysis of the antibiotic producer Nonomuraea sp. ATCC 39727 in different growth conditions

Nonomuraea sp. ATCC 39727 is an aerobic actinomycete, industrially important as a producer of the glycopeptide A40926, which is used as a precursor of the semi-synthetic antibiotic dalbavancin. Previous studies showed that the production of A40926 is depressed by calcium, but promoted by l-glutamine or l-asparagine. In this study, the protein expression changes of Nonomuraea sp. ATCC 39727 in these two different growth and antibiotic-production conditions have been investigated by two-dimensional electrophoresis and mass spectrometry (MS) analysis. Few protein spots show statistically significant expression changes, and, among this group of proteins, malate dehydrogenase (MDH) shows a significant decrease in the overproduction condition. The decrease of MDH is of particular interest because it is the first described significant change in the expression levels of enzymes of the central metabolism related with A40926 overproduction.

Crystal structure of StaL, a glycopeptide antibiotic sulfotransferase from Streptomyces toyocaensis

Over the past decade, antimicrobial resistance has emerged as a major public health crisis. Glycopeptide antibiotics such as vancomycin and teicoplanin are clinically important for the treatment of Gram-positive bacterial infections. StaL is a 3'-phosphoadenosine 5'-phosphosulfate-dependent sulfotransferase capable of sulfating the cross-linked heptapeptide substrate both in vivo and in vitro, yielding the product A47934, a unique teicoplanin-class glycopeptide antibiotic. The sulfonation reaction catalyzed by StaL constitutes the final step in A47934 biosynthesis. Here we report the crystal structure of StaL and its complex with the cofactor product 3'-phosphoadenosine 5'-phosphate. This is only the second prokaryotic sulfotransferase to be structurally characterized. StaL belongs to the large sulfotransferase family and shows higher similarity to cytosolic sulfotransferases (ST) than to the bacterial ST (Stf0). StaL has a novel dimerization motif, different from any other STs that have been structurally characterized. We have also applied molecular modeling to investigate the binding mode of the unique substrate, desulfo-A47934. Based on the structural analysis and modeling results, a series of residues was mutated and kinetically characterized. In addition to the conserved residues (Lys(12), His(67), and Ser(98)), molecular modeling, fluorescence quenching experiments, and mutagenesis studies identified several other residues essential for substrate binding and/or activity, including Trp(34), His(43), Phe(77), Trp(132), and Glu(205).

Resistance to glycopeptide antibiotics in the teicoplanin producer is mediated by van gene homologue expression directing the synthesis of a modified cell wall peptidoglycan

Glycopeptide resistance has been studied in detail in enterococci and staphylococci. In these microorganisms, high-level resistance is achieved by replacing the C-terminal D-alanyl-D-alanine of the nascent peptidoglycan with D-alanyl-D-lactate or D-alanyl-D-serine, thus reducing the affinities of glycopeptides for cell wall targets. Reorganization of the cell wall is directed by the expression of the van gene clusters. The identification of van gene homologs in the genomes of several glycopeptide-producing actinomycetes suggests the involvement of a similar self-resistance mechanism to avoid suicide. This report describes a comprehensive study of self-resistance in Actinoplanes teichomyceticus ATCC 31121, the producer of the clinically relevant glycopeptide teicoplanin. A. teichomyceticus ATCC 31121 showed a MIC of teicoplanin of 25 microg/ml and a MIC of vancomycin of 90 microg/ml during vegetative growth. The vanH, vanA, and vanX genes of A. teichomyceticus were found to be organized in an operon whose transcription was constitutive. Analysis of the UDP-linked peptidoglycan precursors revealed the presence of UDP-glycomuramyl pentadepsipeptide terminating in D-alanyl-D-lactate. No trace of precursors ending in d-alanyl-d-alanine was detected. Thus, the van gene complex was transcribed and expressed in the genetic background of A. teichomyceticus and conferred resistance to vancomycin and teicoplanin through the modification of cell wall biosynthesis. During teicoplanin production (maximum productivity, 70 to 80 microg/ml), the MIC of teicoplanin remained in the range of 25 to 35 microg/ml. Teicoplanin-producing cells were found to be tolerant to high concentrations of exogenously added glycopeptides, which were not bactericidal even at 5,000 microg/ml.

Understanding and manipulating glycopeptide pathways: the example of the dalbavancin precursor A40926

Glycopeptide antibiotics represent an important class of microbial compounds produced by several genera of actinomycetes. The emergence of resistance to glycopeptides among enterococci and staphylococci has prompted the search for second-generation drugs of this class and semi-synthetic derivatives are currently under clinical trials. Dalbavancin is obtained by chemical modification of the natural glycopeptide A40926, produced by a Nonomuraea sp. Recently, there has been considerable progress in the elucidation of biosynthesis of glycopeptide antibiotics; several gene clusters have been characterized, thus providing an understanding of the biosynthesis of these chemically complex molecules. Furthermore, such investigations have yielded the first glycopeptide derivatives produced by genetic or enzymatic intervention. We have isolated and characterized the dbv clusters, involved in the formation of the glycopeptides A40926. The development of a gene-transfer system for Nonomuraea sp. has allowed the manipulation of the A40926 pathway. New derivatives were obtained by inactivating selected dbv genes. In addition, our data suggest differences in the biosynthetic routes for heptapeptide formation between the vancomycin and the teicoplanin families of glycopeptides.

Structure and expression of the atp operon coding for F1F0-ATP synthase from the antibiotic-producing actinomycete Nonomuraea sp. ATCC 39727

Nonomuraea sp. ATCC 39727 is a poorly characterized actinomycete, producer of the glycopeptide antibiotic A40926. In this study, the nucleotide sequence of the atp operon coding for F1F0-ATP synthase of Nonomuraea sp. ATCC 39727 was determined. It consisted of ten open reading frames arranged in the order atpI (encoding the i protein), orfX, atpB (a subunit), atpE (c subunit), atpF (b subunit), atpH (delta subunit), atpA (alpha subunit), atpG (gamma subunit), atpD (beta subunit) and atpC (epsilon subunit). The orfX coded for a putative small hydrophobic 71 amino acid peptide of unknown function related to several bacterial permeases. Its presence appeared to be a distinctive feature of the atp operon of phylogenetically distant actinobacteria. Transcription of the atp operon was evaluated. The results of northern blot and RT-PCR experiments demonstrated that the atp genes were co-transcribed into a single polycistronic mRNA. Real-time RT-PCR data provided evidence showing that transcription of the atp operon was biphasic during Nonomuraea growth. The amount of the atpD transcript decreased at the end of the exponential growth phase, and then moderately increased during the early stationary phase when, in contrast, the levels of ctaC, encoding the cytochrome c oxidase subunit II, progressively decreased. Western blot analysis confirmed that ATP synthase was also present in the membrane during the stationary phase. These results together with previous data demonstrate that oligomycin-sensitive ATP-driven proton pumping activity remained constant in the stationary phase; in contrast, the activity and cytochrome content of the respiratory enzymes became negligible.

Comparative analysis and insights into the evolution of gene clusters for glycopeptide antibiotic biosynthesis

The bal, cep, dbv, sta and tcp gene clusters specify the biosynthesis of the glycopeptide antibiotics balhimycin, chloroeremomycin, A40926, A47934 and teicoplanin, respectively. These structurally related compounds share a similar mechanism of action in their inhibition of bacterial cell wall formation. Comparative sequence analysis was performed on the five gene clusters. Extensive conserved synteny was observed between the bal and cep clusters, which direct the synthesis of very similar compounds but originate from two different species of the genus Amycolatopsis. All other cluster pairs show a limited degree of conserved synteny, involving biosynthetically functional gene cassettes: these include those involved in the synthesis of the carbon backbone of two non-proteinogenic amino acids; in the linkage of amino acids 1--3 and 4--7 in the heptapeptide; and in the formation of the aromatic cross-links. Furthermore, these segments of conserved synteny are often preceded by conserved intergenic regions. Phylogenetic analysis of protein families shows several instances in which relatedness in the chemical structure of the glycopeptides is not reflected in the extent of the relationship of the corresponding polypeptides. Coherent branchings are observed for all polypeptides encoded by the syntenous gene cassettes. These results suggest that the acquisition of distinct, functional genetic elements has played a significant role in the evolution of glycopeptide gene clusters, giving them a mosaic structure. In addition, the synthesis of the structurally similar compounds A40926 and teicoplanin appears as the result of convergent evolution.

Glycopeptide resistance determinants from the teicoplanin producerActinoplanes teichomyceticus

In enterococci and other pathogenic bacteria, high-level resistance to vancomycin and other glycopeptide antibiotics requires the action of the van genes, which direct the synthesis of peptidoglycan terminating in the depsipeptide D-alanyl-D-lactate, in place of the usual D-Ala-D-Ala. The Actinoplanes teichomyceticus tcp cluster, devoted to the biosynthesis of the glycopeptide antibiotic teicoplanin, contains van genes associated to a murF-like sequence (murF2). We show that A. teichomyceticus contains also a house-keeping murF1 gene, capable of complementing a temperature sensitive Escherichia coli murF mutant. MurF1, expressed in Streptomyces lividans, can catalyze the addition of either D-Ala-D-Ala or D-Ala-D-Lac to the UDP-N-acetyl-muramyl-L-Ala-D-Glu-d-Lys. However, similarly expressed MurF2 shows a small enzymatic activity only with D-Ala-D-lactate. Introduction of a single copy of the entire set of van genes confers resistance to teicoplanin-type glycopeptides to S. coelicolor.

Biosynthetic gene cluster of the glycopeptide antibiotic teicoplanin: characterization of two glycosyltransferases and the key acyltransferase

The gene cluster encoding biosynthesis of the clinically important glycopeptide antibiotic teicoplanin has been cloned from Actinoplanes teichomyceticus. Forty-nine putative open reading frames (ORFs) were identified within an 89 kbp genetic locus and assigned roles in teicoplanin biosynthesis, export, resistance, and regulation. Two ORFs, designated orfs 1 and 10*, showed significant homology to known glycosyltransferases. When heterologously expressed in Escherichia coli, these glycosyltransferases were shown to catalyze the transfer of UDP-(N-acetyl)-glucosamine onto, respectively, 3-chloro-beta-hydroxytyrosine-6 (3-Cl-6betaHty) and 4-hydroxyphenylglycine-4 (4Hpg) of the teicoplanin heptapeptide aglycone. The product of another ORF, orf11*, was demonstrated in vitro to transfer n-acetyl-, n-butyryl-, and n-octanoyl-groups from acyl-CoA donors either to a free UDP-aminosugar or to an aminosugar moiety in the teicoplanin pseudoaglycone, thus identifying Orf11* as the key acyltransferase in teicoplanin maturation. These findings should accelerate the combinatorial engineering of new and improved glycopeptide drugs.

Organization of the teicoplanin gene cluster in Actinoplanes teichomyceticus

The glycopeptide teicoplanin is used for the treatment of serious infections caused by Gram-positive pathogens. The tcp gene cluster, devoted to teicoplanin biosynthesis in the actinomycete Actinoplanes teichomyceticus, was isolated and characterized. From sequence analysis, the tcp cluster spans approximately 73 kb and includes 39 ORFs participating in teicoplanin biosynthesis, regulation, resistance and export. Of these, 34 ORFs find a match in at least one of the five glycopeptide gene clusters previously characterized. Putative roles could be assigned for most of the tcp genes. The two glycosyltransferases responsible for attaching amino sugars to amino acids 4 and 6 of the teicoplanin aglycon were overexpressed in Escherichia coli and characterized. They both recognize N-acetylglucosamine as the substrate. tGtfA can add a sugar residue in the presence or absence of N-acetylglucosamine at amino acid 4, while tGtfB can only glycosylate the teicoplanin aglycon.

The biosynthesis of glycopeptide antibiotics?a model for complex, non-ribosomally synthesized, peptidic secondary metabolites

Glycopeptide antibiotics are a class of widely known natural compounds produced by Actinomycetes. Vancomycin, the first member of the glycopeptide family to be discovered, was described in 1955 and used as an antibiotic soon thereafter. During the past 50 years numerous contributions on the structure, mode of action, and therapeutic features of vancomycin have been published. Recently, there has been considerable progress in elucidating the biosynthesis of glycopeptide antibiotics by combining molecular biology and analytical chemistry methods. Here, we provide an overview of the current knowledge regarding biosynthetic glycopeptide assembly.

Improved production of teicoplanin using adsorbent resin in fermentations

AIMS

To use adsorbent resins in fermentations to eliminate toxic effects on growth, reduce feedback repression of production and assist in recovery of teicoplanin.

METHODS AND RESULTS

An adsorbent resin was added to the culture broth for the adsorption of teicoplanin. Amberlite XAD-16, Diaion HP-20, charcoal and silica gel were investigated as adsorbent resins. The adsorbed teicoplanin was extracted from the resin by 80% methanol after fermentation. Antibiotic activity was quantified by the disc-agar diffusion assay against Bacillus substilis, and qualitative evaluations were based on HPLC using YMC-Pack ODS-A column. Diaion HP-20 was the most effective adsorbent resin when added at a concentration of 5% (w/v) in the inoculation stage.

CONCLUSIONS

Addition of Diaion HP-20 in fermentations eliminated toxic effects on growth and reduced feedback repression of teicoplanin by adsorption. There was a 4.2-fold increase in the quantities of teicoplanin. Addition of adsorbent assisted in the recovery of teicoplanin by reducing the recovery steps.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study provide useful information for the production of teicoplanin, a glycopeptide antibiotic produced by Actinoplanes teicomyceticus. Addition of adsorbent in fermentation increased productivity of teicoplanin by more than five times.

Production of teicoplanin by a mutant of Actinoplanes teicomyceticus

Teicoplanin, a glucopeptide antibiotic, was produced by a mutant of Actinoplanes teicomyceticus at 300 mg l-1 using mannose and yeast extract as carbon and nitrogen sources in flask culture and at 500 mg l-1 in 5-1 jar fermenter. Teicoplanin production was 25-fold higher than in the parent strain.

Incorporation of glucose analogs by GtfE and GtfD from the vancomycin biosynthetic pathway to generate variant glycopeptides

Analogs of the glycopeptide antibiotics vancomycin and teicoplanin with alterations in one or both sugar moieties of the disaccharide have been prepared by tandem action of the vancomycin pathway glycosyltransferases GtfE and GtfD. All four regioisomers (2-, 3-, 4-, 6-) of TDP-deoxyglucoses and UDP/TDP-aminoglucoses were prepared, predominantly by action of D-glucopyranosyl-1-phosphate thymidylyltransferase, E(p). GtfE transferred the deoxyglucoses or aminoglucoses onto the 4-OH of 4-hydroxyphenylglycine of both the vancomycin and teicoplanin aglycone scaffolds. Kinetic analysis indicated the 2-, 3-, 4-, and 6-amino-glucoses were transferred by GtfE with only a 4- to 30-fold drop in k(cat) and no effect on K(m) compared to the native substrate, UDP/TDP-glucose, suggesting preparative utility. The next enzyme, GtfD, could utilize the variant glucosyl-peptides as substrates for transfer of L-4-epi-vancosamine. The aminosugar moieties in these variant glycopeptides introduce sites for acylation or reductive alkylation.

Production of teicoplanin by Actinoplanes teichomyceticus in continuous fermentation

Production of the potent antibiotic teicoplanin by Actinoplanes teichomyceticus was studied in batch and in chemostat cultures. It is found that the producing strain deactivates to a non-producing strain named NP-12. This strain is used to find the growth kinetics of the A. teichomyceticus without interference from the product teicoplanin. In batch experiments with NP-12 grown on glucose at different initial concentrations and with different added amounts of teicoplanin, the strong inhibitory effect of teicoplanin was determined. These results obtained on NP-12 were validated in a series of chemostat experiments with the processing strain. All experiments in batch and in chemostat cultures were well represented by Monod kinetics with respect to the carbon and energy source (glucose) and with a substantial inhibitory effect of teicoplanin. Further experiments were made with the producing strain in a continuous reactor coupled to a microfilter that delivers a cell-free permeate. It was found that the derived kinetics almost exactly simulated the behavior of the cell recirculation reactor in addition to when the cell concentration in the reactor was more than four times higher than in the chemostat. For industrial production of teicoplanin, a continuous reactor with cell recirculation and working with a low effluent glucose concentration was by far the best mode of operation. Finally, the deactivation of the producing strain to NP-12 was modeled by a two-step deactivation mechanism. Deactivation was independent of dilution rate but dependent on the inoculum preparation and on the previous history of the inoculum.

Production of teicoplanin by valine analogue-resistant mutant strains of Actinoplanes teichomyceticus

Teicoplanin is a glycopeptide antibiotic produced by Actinoplanes teichomyceticus. A strain improvement to increase the productivity of the major component, teicoplanin A2-2, was carried out. As the fatty moiety of teicoplanin A2-2 is derived from L-valine, L-valine analogue (valine hydroxamate)-resistant mutants were derived. One of the mutants, 98-1-227, overproduced valine and produced a higher titer of total teicoplanin with higher A2-2 content. In a pilot fermentor (7 m3), the total productivity of teicoplanin was 1,800 units/ml and the A2-2 content was 58%.

Tandem action of glycosyltransferases in the maturation of vancomycin and teicoplanin aglycones: novel glycopeptides

The glycopeptides vancomycin and teicoplanin are clinically important antibiotics. The carbohydrate portions of these molecules affect biological activity, and there is great interest in developing efficient strategies to make carbohydrate derivatives. To this end, genes encoding four glycosyltransferases, GtfB, C, D, E, were subcloned from Amycolatopsis orientalis strains that produce chloroeremomycin (GtfB, C) or vancomycin (GtfD, E) into Escherichia coli. After expression and purification, each glycosyltransferase (Gtf) was characterized for activity either with the aglycones (GtfB, E) or the glucosylated derivatives (GtfC, D) of vancomycin and teicoplanin. GtfB efficiently glucosylates vancomycin aglycone using UDP-glucose as the glycosyl donor to form desvancosaminyl-vancomycin (vancomycin pseudoaglycone), with k(cat) of 17 min(-1), but has very low glucosylation activity, < or = 0.3 min(-1), for an alternate substrate, teicoplanin aglycone. In contrast, GtfE is much more efficient at glucosylating both its natural substrate, vancomycin aglycone (k(cat) = 60 min(-1)), and an unnatural substrate, teicoplanin aglycone (k(cat) = 20 min(-1)). To test the addition of the 4-epi-vancosamine moiety by GtfC and GtfD, synthesis of UDP-beta-L-4-epi-vancosamine was undertaken. This NDP-sugar served as a substrate for both GtfC and GtfD in the presence of vancomycin pseudoaglycone (GtfC and GtfD) or the glucosylated teicoplanin scaffold, 7 (GtfD). The GtfC product was the 4-epi-vancosaminyl form of vancomycin. Remarkably, GtfD was able to utilize both an unnatural acceptor, 7, and an unnatural nucleotide sugar donor, UDP-4-epi-vancosamine, to synthesize a novel hybrid teicoplanin/vancomycin glycopeptide. These results establish the enzymatic activity of these four Gtfs, begin to probe substrate specificity, and illustrate how they can be utilized to make variant sugar forms of both the vancomycin and the teicoplanin class of glycopeptide antibiotics.

Teicoplanin biosynthesis genes in Actinoplanes teichomyceticus

The genetic determinants for the biosynthesis of the glycopeptide antibiotic teicoplanin were identified. In order to isolate the corresponding gene cluster, oligonucleotides derived from highly conserved motifs in peptide synthetases were used. These synthetic probes, and gene fragments derived from the balhimycin gene cluster of Amycolatopsis mediterranei, led to the identification of the likely teicoplanin gene cluster centered on a region of ca. 110 kb from the genome of Actinoplanes teichomyceticus, the teicoplanin producer. Partial nucleotide sequences identified partial ORFs likely to encode two glycosyltransferases, three P-450 monooxygenases and one ABC transporter. The corresponding genes have been found in other glycopeptide gene clusters. Furthermore, upstream to the peptide synthetase region a segment was identified with a remarkable similarity to the vanHAX operon, conferring resistance to glycopeptides in enterococci. Thus, in contrast to the other glycopeptide producers thus far analyzed, in A. teichomyceticus the genes for teicoplanin biosynthesis are closely linked to homologs of glycopeptide resistance commonly found in vancomycin-resistant enterococci.

Biosynthetic studies of the glycopeptide teicoplanin by (1)H and (13)C NMR

The biosynthesis of the glycopeptide antibiotic teicoplanin was studied by growing a teicoplanin producing strain of Actinoplanes teichomyceticus (ATCC 31121) on glucose containing either 34.0% [1-(13)C]glucose or 9.7% [U-(13)C]glucose. The fractional enrichment pattern of teicoplanin produced in the medium containing [1-(13)C]glucose was obtained from a one-dimensional (13)C spectrum. The enrichment pattern showed characteristic peaks indicating that amino acids 3 and 7 are derived from acetate, whereas amino acids 1, 2, 4, 5, and 6 are derived from tyrosine. Multiplet structures in heteronuclear single quantum coherence spectra of teicoplanin produced in the medium containing [U-(13)C]glucose showed characteristic coupling patterns supporting these results. Fractional enrichment patterns and multiplet structures of the three sugars in teicoplanin showed that about 50% of the sugars have the same labeling pattern as the glucose substrate whereas the rest have a labeling pattern showing that they are reassembled, probably from precursors in the primary metabolism.

Growth and production kinetics of a teicoplanin producing strain of Actinoplanes teichomyceticus

The growth and production kinetics of a teicoplanin producing strain of Actinoplanes teichomyceticus (ATCC 31121) was investigated during batch cultivations on defined media. The growth was characterised by two exponential growth phases (EGPs), with a higher specific growth rate in the first than in the second phase. Also the specific rate of formation of teicoplanin was significantly lower in the second phase than in the first phase. This two-phased growth pattern was suggested to be caused by inhibition of growth by teicoplanin accumulated. Furthermore high concentrations of ammonia or phosphate reduced both the specific growth rate in the first EGP and the total production of teicoplanin.