Lincomycin, cultivation of producing strains and biosynthesis

Transcriptional regulators of secondary metabolite biosynthesis in Streptomyces

In the post-genome era, great progress has been made in metabolic engineering using recombinant DNA technology to enhance the production of high-value products by Streptomyces. With the development of microbial genome sequencing techniques and bioinformatic tools, a growing number of secondary metabolite (SM) biosynthetic gene clusters in Streptomyces and their biosynthetic logics have been uncovered and elucidated. In order to increase our knowledge about transcriptional regulators in SM of Streptomyces, this review firstly makes a comprehensive summary of the characterized factors involved in enhancing SM production and awakening SM biosynthesis. Future perspectives on transcriptional regulator engineering for new SM biosynthesis by Streptomyces are also provided.

Lincosamide Antibiotics: Structure, Activity, and Biosynthesis

Lincosamides are naturally occurring antibiotics isolated from Streptomyces sp. Currently, lincomycin A and its semisynthetic analogue clindamycin are used as clinical drugs. Due to their unique structures and remarkable biological activities, derivatizations of lincosamides via semi-synthesis and biosynthetic studies have been reported. This review summarizes the structures and biological activities of lincosamides, and the recent studies of lincosamide biosynthetic enzymes.

Characterization of a TetR-type positive regulator AtrA for lincomycin production in Streptomyces lincolnensis

AtrA belongs to the TetR family and has been well characterized for its roles in antibiotic biosynthesis regulation. Here, we identified an AtrA homolog (AtrA-lin) in Streptomyces lincolnensis. Disruption of atrA-lin resulted in reduced lincomycin production, whereas the complement restored the lincomycin production level to that of the wild-type. In addition, atrA-lin disruption did not affect cell growth and morphological differentiation. Furthermore, atrA-lin disruption hindered the transcription of regulatory gene lmbU, structural genes lmbA and lmbW inside the lincomycin biosynthesis gene cluster, and 2 other regulatory genes, adpA and bldA. Completement of atrA-lin restored the transcription of these genes to varying degrees. Notably, we found that AtrA-lin directly binds to the promoter region of lmbU. Collectively, AtrA-lin positively modulated lincomycin production via both pathway-specific and global regulators. This study offers further insights into the functional diversity of AtrA homologs and the mechanism of lincomycin biosynthesis regulation.

An alternative σ factor σLsl regulates lincomycin production in Streptomyces lincolnensis

Lincomycin produced by Streptomyces lincolnensis is a critical antibacterial antibiotic in the clinical. To further understand the regulatory mechanism of lincomycin biosynthesis, we identified an alternative σ factor, σLsl, in Streptomyces lincolnensis NRRL 2936. Deletion of sigLsl resulted in an increase in cell growth but a decrease in lincomycin production. σLsl boosted lincomycin biosynthesis by directly stimulating the transcription of four genes (lmbD, lmbV, lmrC, and lmbU) within the lincomycin biosynthetic lmb gene cluster. Besides, σLsl participated in lincomycin biosynthesis by directly stimulating the transcription of mshC, a gene responsible for MSH synthesis. In conclusion, our findings demonstrated that σLsl plays a direct regulatory role in lincomycin biosynthesis. This study extends the understanding of molecular mechanisms of lincomycin biosynthetic regulation.

An alternative σ factor σL sl regulates lincomycin production in Streptomyces lincolnensis

Lincomycin produced by Streptomyces lincolnensis is a critical antibacterial antibiotic in the clinical. To further understand the regulatory mechanism of lincomycin biosynthesis, we identified an alternative σ factor, σ^L _sl , in Streptomyces lincolnensis NRRL 2936. Deletion of sigL_sl resulted in an increase in cell growth but a decrease in lincomycin production. σ^L _sl boosted lincomycin biosynthesis by directly stimulating the transcription of four genes (lmbD, lmbV, lmrC, and lmbU) within the lincomycin biosynthetic lmb gene cluster. Besides, σ^L _sl participated in lincomycin biosynthesis by directly stimulating the transcription of mshC, a gene responsible for MSH synthesis. In conclusion, our findings demonstrated that σ^L _sl plays a direct regulatory role in lincomycin biosynthesis. This study extends the understanding of molecular mechanisms of lincomycin biosynthetic regulation.

Simultaneous improvement of lincomycin A production and reduction of lincomycin B levels in Streptomyces lincolnensis using a combined medium optimization approach

Purpose

The current study aimed to optimize the culture and production parameters of industrial production of lincomycin A by Streptomyces lincolnensis using a statistical approach that could also reduce unwanted by-products.

Methods

The Plackett-Burman design, steepest ascent method, and response surface design were used to evaluate different factors that affect lincomycin A production.

Results

Using an optimized S. lincolnensis fermentation medium, lincomycin A production was increased up to 4600 mg/L in shaking flasks, which indicated a 28.3% improvement over previous production in an un-optimized medium (3585 mg/L). Additionally, the concentration of lincomycin B by-product was reduced to 0.8%, which was 82.2% lower than that in the un-optimized medium. Further, quantitative real-time PCR analysis revealed the optimized medium improved lincomycin A production by stimulating key genes in the lincomycin A biosynthesis pathway, as well as an osmotic stress gene.

Conclusions

Based on the results, the sequential optimization strategy in this study provides powerful means for the enhancement of lincomycin A with less by-product. We found that osmotic stress reduced the concentration of lincomycin B, which could also help reduce fermentation by-product yields in other actinobacteria.

A putative redox‐sensing regulator Rex regulates lincomycin biosynthesis in Streptomyces lincolnensis

Lincomycin is an important antimicrobial agent which is widely used in clinical and animal husbandry. The biosynthetic pathway of lincomycin comes to light in the past 10 years, however, the regulatory mechanism is still unclear. In this study, a redox‐sensing regulator Rex from Streptomyces lincolnensis (Rexlin) was identified and characterized to affect cell growth and lincomycin biosynthesis. Disruption of rex resulted in an increase in cell growth, but a decrease in lincomycin production. The results of quantitative real‐time polymerase chain reaction showed that Rexlin can promote transcription of the regulatory gene lmbU and the structural genes lmbA, lmbC, lmbJ, lmbV, and lmbW. However, electrophoretic mobility shift assay analysis demonstrated that Rexlin can not bind to the promoter regions of these genes above. Findings in this study broadened our horizons in the regulatory mechanism of lincomycin production and laid a foundation for strain improvement of antibiotic producers.

A putative redox-sensing regulator Rex regulates lincomycin biosynthesis in Streptomyces lincolnensis

Lincomycin is an important antimicrobial agent which is widely used in clinical and animal husbandry. The biosynthetic pathway of lincomycin comes to light in the past 10 years, however, the regulatory mechanism is still unclear. In this study, a redox-sensing regulator Rex from Streptomyces lincolnensis (Rex_lin ) was identified and characterized to affect cell growth and lincomycin biosynthesis. Disruption of rex resulted in an increase in cell growth, but a decrease in lincomycin production. The results of quantitative real-time polymerase chain reaction showed that Rex_lin can promote transcription of the regulatory gene lmbU and the structural genes lmbA, lmbC, lmbJ, lmbV, and lmbW. However, electrophoretic mobility shift assay analysis demonstrated that Rex_lin can not bind to the promoter regions of these genes above. Findings in this study broadened our horizons in the regulatory mechanism of lincomycin production and laid a foundation for strain improvement of antibiotic producers.

Actinomycetes: A Never-Ending Source of Bioactive Compounds-An Overview on Antibiotics Production

The discovery of penicillin by Sir Alexander Fleming in 1928 provided us with access to a new class of compounds useful at fighting bacterial infections: antibiotics. Ever since, a number of studies were carried out to find new molecules with the same activity. Microorganisms belonging to Actinobacteria phylum, the Actinomycetes, were the most important sources of antibiotics. Bioactive compounds isolated from this order were also an important inspiration reservoir for pharmaceutical chemists who realized the synthesis of new molecules with antibiotic activity. According to the World Health Organization (WHO), antibiotic resistance is currently one of the biggest threats to global health, food security, and development. The world urgently needs to adopt measures to reduce this risk by finding new antibiotics and changing the way they are used. In this review, we describe the primary role of Actinomycetes in the history of antibiotics. Antibiotics produced by these microorganisms, their bioactivities, and how their chemical structures have inspired generations of scientists working in the synthesis of new drugs are described thoroughly.

Comparative transcriptomic analysis reveals the significant pleiotropic regulatory effects of LmbU on lincomycin biosynthesis

Background

Lincomycin, produced by Streptomyces lincolnensis, is a lincosamide antibiotic and widely used for the treatment of the infective diseases caused by Gram-positive bacteria. The mechanisms of lincomycin biosynthesis have been deeply explored in recent years. However, the regulatory effects of LmbU that is a transcriptional regulator in lincomycin biosynthetic (lmb) gene cluster have not been fully addressed.

Results

LmbU was used to search for homologous LmbU (LmbU-like) proteins in the genomes of actinobacteria, and the results showed that LmbU-like proteins are highly distributed regulators in the biosynthetic gene clusters (BGCs) of secondary metabolites or/and out of the BGCs in actinomycetes. The overexpression, inactivation and complementation of the lmbU gene indicated that LmbU positively controls lincomycin biosynthesis in S. lincolnensis. Comparative transcriptomic analysis further revealed that LmbU activates the 28 lmb genes at whole lmb cluster manner. Furthermore, LmbU represses the transcription of the non-lmb gene hpdA in the biosynthesis of l-tyrosine, the precursor of lincomycin. LmbU up-regulates nineteen non-lmb genes, which would be involved in multi-drug flux to self-resistance, nitrate and sugar transmembrane transport and utilization, and redox metabolisms.

Conclusions

LmbU is a significant pleiotropic transcriptional regulator in lincomycin biosynthesis by entirely activating the lmb cluster and regulating the non-lmb genes in Streptomyces lincolnensis. Our results first revealed the pleiotropic regulatory function of LmbU, and shed new light on the transcriptional effects of LmbU-like family proteins on antibiotic biosynthesis in actinomycetes.

AdpAlin, a Pleiotropic Transcriptional Regulator, Is Involved in the Cascade Regulation of Lincomycin Biosynthesis in Streptomyces lincolnensis

Lincomycin is one of the most important antibiotics in clinical practice. To further understand the regulatory mechanism on lincomycin biosynthesis, we investigated a pleiotropic transcriptional regulator AdpA_lin in the lincomycin producer Streptomyces lincolnensis NRRL 2936. Deletion of adpA _lin (which generated ΔadpA _lin ) interrupted lincomycin biosynthesis and impaired the morphological differentiation. We also found that putative AdpA binding sites were unusually scattered in the promoters of all the 8 putative operons in the lincomycin biosynthetic gene cluster (BGC). In ΔadpA _lin , transcript levels of structural genes in 8 putative operons were decreased with varying degrees, and electrophoretic mobility shift assays (EMSAs) confirmed that AdpA_lin activated the overall putative operons via directly binding to their promoter regions. Thus, we speculated that the entire lincomycin biosynthesis is under the control of AdpA_lin. Besides, AdpA_lin participated in lincomycin biosynthesis by binding to the promoter of lmbU which encoded a cluster sited regulator (CSR) LmbU of lincomycin biosynthesis. Results of qRT-PCR and catechol dioxygenase activity assay showed that AdpA_lin activated the transcription of lmbU. In addition, AdpA_lin activated the transcription of the bldA by binding to its promoter, suggesting that AdpA_lin indirectly participated in lincomycin biosynthesis and morphological differentiation. Uncommon but understandable, AdpA_lin auto-activated its own transcription via binding to its own promoter region. In conclusion, we provided a molecular mechanism around the effect of AdpA_lin on lincomycin biosynthesis in S. lincolnensis, and revealed a cascade regulation of lincomycin biosynthesis by AdpA_lin, LmbU, and BldA.

TetR-Type Regulator SLCG_2919 Is a Negative Regulator of Lincomycin Biosynthesis in Streptomyces lincolnensis

Lincomycin A (Lin-A) is a widely used antibacterial antibiotic fermented by Streptomyces lincolnensis However, the transcriptional regulatory mechanisms underlying lincomycin biosynthesis have seldom been investigated. Here, we first identified a TetR family transcriptional regulator (TFR), SLCG_2919, which negatively modulates lincomycin biosynthesis in S. lincolnensis LCGL. SLCG_2919 was found to specifically bind to promoter regions of the lincomycin biosynthetic gene cluster (lin cluster), including 25 structural genes, three resistance genes, and one regulatory gene, and to inhibit the transcription of these genes, demonstrating a directly regulatory role in lincomycin biosynthesis. Furthermore, we found that SLCG_2919 was not autoregulated, but directly repressed its adjacent gene, SLCG_2920, which encodes an ATP/GTP binding protein whose overexpression increased resistance against lincomycin and Lin-A yields in S. lincolnensis The precise SLCG_2919 binding site within the promoter region of SLCG_2920 was determined by a DNase I footprinting assay and by electrophoretic mobility shift assays (EMSAs) based on base substitution mutagenesis, with the internal 10-nucleotide (nt) AT-rich sequence (AAATTATTTA) shown to be essential for SLCG_2919 binding. Our findings indicate that SLCG_2919 is a negative regulator for controlling lincomycin biosynthesis in S. lincolnensis The present study improves our understanding of molecular regulation for lincomycin biosynthesis.IMPORTANCE TetR family transcriptional regulators (TFRs) are generally found to regulate diverse cellular processes in bacteria, especially antibiotic biosynthesis in Streptomyces species. However, knowledge of their function in lincomycin biosynthesis in S. lincolnensis remains unknown. The present study provides a new insight into the regulation of lincomycin biosynthesis through a TFR, SLCG_2919, that directly modulates lincomycin production and resistance. Intriguingly, SLCG_2919 and its adjoining gene, SLCG_2920, which encodes an ATP/GTP binding protein, were extensively distributed in diverse Streptomyces species. In addition, we revealed a new TFR binding motif, in which SLCG_2919 binds to the promoter region of SLCG_2920, dependent on the intervening AT-rich sequence rather than on the flanking inverted repeats found in the binding sites of other TFRs. These insights into transcriptional regulation of lincomycin biosynthesis by SLCG_2919 will be valuable in paving the way for genetic engineering of regulatory elements in Streptomyces species to improve antibiotic production.

Global regulator BldA regulates morphological differentiation and lincomycin production in Streptomyces lincolnensis

Global regulator BldA, the only tRNA for a rare leucine codon UUA, is best known for its ability to affect morphological differentiation and secondary metabolism in the genus Streptomyces. In this study, we confirmed the regulatory function of the bldA gene (Genbank accession no. EU124663.1) in Streptomyces lincolnensis. Disruption of bldA hinders the sporulation and lincomycin production, that can recur when complemented with a functional bldA gene. Western blotting assays demonstrate that translation of the lmbB2 gene which encodes a L-tyrosine hydroxylase is absolutely dependent on BldA; however, mistranslation of the lmbU gene which encodes a cluster-situated regulator (CSR) is observed in a bldA mutant. Intriguingly, when the preferential cognate codon CTG was used, the expression level of LmbU was not the highest compared to the usage of rare codon TTA or CTA, indicating the rare codon in this position is significant for the regulation of lmbU expression. Moreover, replacement of TTA codons in both genes with another leucin codon in the bldA mutant did not restore lincomycin production. Thus, we believe that the bldA gene regulates lincomycin production via controlling the translation of not only lmbB2 and lmbU, but also the other TTA-containing genes. In conclusion, the present study demonstrated the importance of the bldA gene in morphological differentiation and lincomycin production in S. lincolnensis.

The Novel Transcriptional Regulator LmbU Promotes Lincomycin Biosynthesis through Regulating Expression of Its Target Genes in Streptomyces lincolnensis

Lincomycin A is a clinically important antimicrobial agent produced by Streptomyces lincolnensis In this study, a new regulator designated LmbU (GenBank accession no. ABX00623.1) was identified and characterized to regulate lincomycin biosynthesis in S. lincolnensis wild-type strain NRRL 2936. Both inactivation and overexpression of lmbU resulted in significant influences on lincomycin production. Transcriptional analysis and in vivo neomycin resistance (Neo^r) reporter assays demonstrated that LmbU activates expression of the lmbA, lmbC, lmbJ, and lmbW genes and represses expression of the lmbK and lmbU genes. Electrophoretic mobility shift assays (EMSAs) demonstrated that LmbU can bind to the regions upstream of the lmbA and lmbW genes through the consensus and palindromic sequence 5'-CGCCGGCG-3'. However, LmbU cannot bind to the regions upstream of the lmbC, lmbJ, lmbK, and lmbU genes as they lack this motif. These data indicate a complex transcriptional regulatory mechanism of LmbU. LmbU homologues are present in the biosynthetic gene clusters of secondary metabolites of many other actinomycetes. Furthermore, the LmbU homologue from Saccharopolyspora erythraea (GenBank accession no. WP_009944629.1) also binds to the regions upstream of lmbA and lmbW, which suggests widespread activity for this regulator. LmbU homologues have no significant structural similarities to other known cluster-situated regulators (CSRs), which indicates that they belong to a new family of regulatory proteins. In conclusion, the present report identifies LmbU as a novel transcriptional regulator and provides new insights into regulation of lincomycin biosynthesis in S. lincolnensisIMPORTANCE Although lincomycin biosynthesis has been extensively studied, its regulatory mechanism remains elusive. Here, a novel regulator, LmbU, which regulates transcription of its target genes in the lincomycin biosynthetic gene cluster (lmb gene cluster) and therefore promotes lincomycin biosynthesis, was identified in S. lincolnensis strain NRRL 2936. Importantly, we show that this new regulatory element is relatively widespread across diverse actinomycetes species. In addition, our findings provide a new strategy for improvement of yield of lincomycin through manipulation of LmbU, and this approach could also be evaluated in other secondary metabolite gene clusters containing this regulatory protein.

Lincosamides: Chemical structure, biosynthesis, mechanism of action, resistance, and applications

Lincomycin and its derivatives are antibiotics exhibiting biological activity against bacteria, especially Gram-positive ones, and also protozoans. Lincomycin and its semi-synthetic chlorinated derivative clindamycin are widely used in clinical practice. Both antibiotics are bacteriostatic, inhibiting protein synthesis in sensitive bacteria; however, at higher concentrations, they may be bactericidal. Clindamycin is usually much more active than lincomycin in the treatment of bacterial infections, in particular those caused by anaerobic species; it can also be used for the treatment of important protozoal diseases, e.g. malaria, most effectively in combination with other antibiotic or non-antibiotic antimicrobials (primaquine, fosfidomycin, benzoyl peroxide). Chemical structures of lincosamide antibiotics and the biosynthesis of lincomycin and its genetic control have been summarized and described. Resistance to lincomycin and clindamycin may be caused by methylation of 23S ribosomal RNA, modification of the antibiotics by specific enzymes or active efflux from the bacterial cell.

Copper-catalyzed oxidative oxyalkylation of enol ethers with α-amino carbonyl compounds and hydroperoxides

The first example of alkene oxyalkylation through C(sp³)–H functionalization is described for the synthesis of 2-amino-3,4-dioxy carbonyl compounds.

Structure and possible mechanism of the CcbJ methyltransferase from Streptomyces caelestis

The S-adenosyl-L-methionine (SAM)-dependent methyltransferase CcbJ from Streptomyces caelestis catalyzes one of the final steps in the biosynthesis of the antibiotic celesticetin, methylation of the N atom of its proline moiety, which greatly enhances the activity of the antibiotic. Since several celesticetin variants exist, this enzyme may be able to act on a variety of substrates. The structures of CcbJ determined by MAD phasing at 3.0 Å resolution, its native form at 2.7 Å resolution and its complex with S-adenosyl-L-homocysteine (SAH) at 2.9 Å resolution are reported here. Based on these structures, three point mutants, Y9F, Y17F and F117G, were prepared in order to study its behaviour as well as docking simulations of both CcbJ-SAM-substrate and CcbJ-SAH-product complexes. The structures show that CcbJ is a class I SAM-dependent methyltransferase with a wide active site, thereby suggesting that it may accommodate a number of different substrates. The mutation results show that the Y9F and F117G mutants are almost non-functional, while the Y17F mutant has almost half of the wild-type activity. In combination with the docking studies, these results suggest that Tyr9 and Phe117 are likely to help to position the substrate for the methyl-transfer reaction and that Tyr9 may also facilitate the reaction by removing an H(+) ion. Tyr17, on the other hand, seems to operate by helping to stabilize the SAM cofactor.

Biodiversity in production of antibiotics and other bioactive compounds

Microbes continue to play a highly considerable role in the drug discovery and development process. Nevertheless, the number of new chemical entities (NCEs) of microbial origin that has been approved by the Food and Drug Administration (FDA) has been reduced in the past decade. This scarcity can be partly attributed to the redundancy in the discovered molecules from microbial isolates, which are isolated from common terrestrial ecological units. However, this situation can be partly overcome by exploring rarely exploited ecological niches as the source of microbes, which reduces the chances of isolating compounds similar to existing ones. The use of modern and advanced isolation techniques, modification of the existing fermentation methods, genetic modifications to induce expression of silent genes, analytical tools for the detection and identification of new chemical entities, use of polymers in fermentation to enhance yield of fermented compounds, and so on, have all aided in enhancing the frequency of acquiring novel compounds. These compounds are representative of numerous classes of diverse compounds. Thus, compounds of microbial origin and their analogues undergoing clinical trials continue to demonstrate the importance of compounds from microbial sources in modern drug discovery.

Use of lincomycin-impregnated demineralized freeze-dried bone allograft in the periodontal defect after third molar surgery

PURPOSE

The aim of the present study was to evaluate the periodontal regenerative capacity of demineralized freeze-dried bone allograft (DFDBA) alone or used with local lincomycin.

MATERIALS AND METHODS

In the present single-blind, randomized, controlled clinical trial, 20 subjects 26 years old or older, requiring extraction of bilateral third molars (M3s), were included. Each subject was randomly assigned to receive either DFDBA or DFDBA plus lincomycin therapy. Within the subjects, 1 M3 site was randomly selected to be the experimental site and the contralateral served as the control and was permitted to heal without intervention. The primary variables were changes in the probing depth (PD), clinical alveolar bone levels (ABLs), and radiographic alveolar bone density (ABD) on the distal aspect of second molar between baseline (immediately postoperatively) and 26 weeks postoperatively (T26). Appropriate sample sizes and descriptive, bivariate, and multivariate statistics were computed.

RESULTS

For both treatment and control sites, between T0 and T26, statistically significant improvements were seen in the ABLs and ABD (P < .05). Within-subject comparisons showed no significant differences in PD, ABL, or ABD between the treatment and control M3 sites at T0 or T26 (P > .05). Also, no significant differences were found in the PD, ABL, or ABD between the 2 treatment M3 sites at T26 (P > .05).

CONCLUSIONS

The results of the present study have revealed that the PD, ABL, and ABD improved after M3 removal in subjects 26 years old or older, irrespective of the treatment or control group. Reconstructive procedures (e.g., DFDBA with or without lincomycin therapy) did not offer predictable benefits compared with a no-treatment protocol in patients younger than 30 years old.

Lincomycin biosynthesis involves a tyrosine hydroxylating heme protein of an unusual enzyme family

The gene lmbB2 of the lincomycin biosynthetic gene cluster of Streptomyces lincolnensis ATCC 25466 was shown to code for an unusual tyrosine hydroxylating enzyme involved in the biosynthetic pathway of this clinically important antibiotic. LmbB2 was expressed in Escherichia coli, purified near to homogeneity and shown to convert tyrosine to 3,4-dihydroxyphenylalanine (DOPA). In contrast to the well-known tyrosine hydroxylases (EC 1.14.16.2) and tyrosinases (EC 1.14.18.1), LmbB2 was identified as a heme protein. Mass spectrometry and Soret band-excited Raman spectroscopy of LmbB2 showed that LmbB2 contains heme b as prosthetic group. The CO-reduced differential absorption spectra of LmbB2 showed that the coordination of Fe was different from that of cytochrome P450 enzymes. LmbB2 exhibits sequence similarity to Orf13 of the anthramycin biosynthetic gene cluster, which has recently been classified as a heme peroxidase. Tyrosine hydroxylating activity of LmbB2 yielding DOPA in the presence of (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4) was also observed. Reaction mechanism of this unique heme peroxidases family is discussed. Also, tyrosine hydroxylation was confirmed as the first step of the amino acid branch of the lincomycin biosynthesis.

The biosynthesis of nitrogen-, sulfur-, and high-carbon chain-containing sugars

Carbohydrates serve many structural and functional roles in biology. While the majority of monosaccharides are characterized by the chemical composition (CH2O)n, modifications including deoxygenation, C-alkylation, amination, O- and N-methylation, which are characteristic of many sugar appendages of secondary metabolites, are not uncommon. Interestingly, some sugar molecules are formed via modifications including amine oxidation, sulfur incorporation, and "high-carbon" chain attachment. Most of these unusual sugars have been identified over the past several decades as components of microbially produced natural products, although a few high-carbon sugars are also found in the lipooligosaccharides of the outer cell walls of Gram-negative bacteria. Despite their broad distribution in nature, these sugars are considered "rare" due to their relative scarcity. The biosynthetic steps that underlie their formation continue to perplex researchers to this day and many questions regarding key transformations remain unanswered. This review will focus on our current understanding of the biosynthesis of unusual sugars bearing oxidized amine substituents, thio-functional groups, and high-carbon chains.

Construction of the octose 8-phosphate intermediate in lincomycin A biosynthesis: characterization of the reactions catalyzed by LmbR and LmbN

Lincomycin A is a potent antimicrobial agent noted for its unusual C1 methylmercapto-substituted 8-carbon sugar. Despite its long clinical history for the treatment of Gram-positive infections, the biosynthesis of the C(8)-sugar, methylthiolincosamide (MTL), is poorly understood. Here, we report our studies of the two initial enzymatic steps in the MTL biosynthetic pathway leading to the identification of D-erythro-D-gluco-octose 8-phosphate as a key intermediate. Our experiments demonstrate that this intermediate is formed via a transaldol reaction catalyzed by LmbR using D-fructose 6-phosphate or D-sedoheptulose 7-phosphate as the C(3) donor and D-ribose 5-phosphate as the C(5) acceptor. Subsequent 1,2-isomerization catalyzed by LmbN converts the resulting 2-keto C(8)-sugar (octulose 8-phosphate) to octose 8-phosphate. These results provide, for the first time, in vitro evidence for the biosynthetic origin of the C(8) backbone of MTL.

Catalytic promiscuity of a bacterial α-N-methyltransferase

The posttranslational methylation of N-terminal α-amino groups (α-N-methylation) is a ubiquitous reaction found in all domains of life. Although this modification usually occurs on protein substrates, recent studies have shown that it also takes place on ribosomally synthesized natural products. Here we report an investigation of the bacterial α-N-methyltransferase CypM involved in the biosynthesis of the peptide antibiotic cypemycin. We demonstrate that CypM has low substrate selectivity and methylates a variety of oligopeptides, cyclic peptides such as nisin and haloduracin, and the ε-amino group of lysine. Hence it may have potential for enzyme engineering and combinatorial biosynthesis. Bayesian phylogenetic inference of bacterial α-N-methyltransferases suggests that they have not evolved as a specific group based on the chemical transformations they catalyze, but that they have been acquired from various other methyltransferase classes during evolution.

New carbasugars from Streptomyces lincolnensis

Two new carbasugars (9 and 10) were isolated from Streptomyces lincolnensis DSM 40355 along with streptol (valienol, 8), gabosine I (valienone, 14), and glucosylglycerate. The reported (1)H and (13)C assignments are based on 1D ((1)H, (13)C, 1D-TOCSY, homodecoupling) and 2D (gCOSY, J-resolved, TOCSY, ROESY, gHSQC, gHMBC) NMR techniques and electrospray ionization FT mass spectrometry (ESI FTMS).

Sweet antibiotics - the role of glycosidic residues in antibiotic and antitumor activity and their randomization

A large number of antibiotics are glycosides. In numerous cases the glycosidic residues are crucial to their activity; sometimes, glycosylation only improves their pharmacokinetic parameters. Recent developments in molecular glycobiology have improved our understanding of aglycone vs. glycoside activities and made it possible to develop new, more active or more effective glycodrugs based on these findings - a very illustrative recent example is vancomycin. The majority of attention has been devoted to glycosidic antibiotics including their past, present, and probably future position in antimicrobial therapy. The role of the glycosidic residue in the biological activity of glycosidic antibiotics, and the attendant targeting and antibiotic selectivity mediated by glycone and aglycone in antibiotics some antitumor agents is discussed here in detail. Chemical and enzymatic modifications of aglycones in antibiotics, including their synthesis, are demonstrated on various examples, with particular emphasis on the role of specific and mutant glycosyltransferases and glycorandomization in the preparation of these compounds. The last section of this review describes and explains the interactions of the glycone moiety of the antibiotics with DNA and especially the design and structure-activity relationship of glycosidic antibiotics, including their classification based on their aglycone and glycosidic moiety. The new enzymatic methodology 'glycorandomization' enabled the preparation of glycoside libraries and opened up new ways to prepare optimized or entirely novel glycoside antibiotics.

Lincomycin, clindamycin and their applications

Lincomycin and clindamycin are lincosamide antibiotics used in clinical practice. Both antibiotics are bacteriostatic and inhibit protein synthesis in sensitive bacteria. They may even be bactericidal at the higher concentrations that can be reached in vivo. Clindamycin is usually more active than lincomycin in the treatment of bacterial infections, in particular those caused by anaerobic species; and it can also be used for the treatment of important protozoal diseases, e.g. malaria, most effectively in combination with primaquine. Resistance to lincomycin and clindamycin may be caused by methylation of 23S ribosomal RNA, modification of the antibiotics by specific enzymes or active efflux from the periplasmic space.