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The review (with 214 references cited) is devoted to moenomycins, the only known group of antibiotics that directly inhibit bacterial peptidoglycan glycosytransferases. Naturally occurring moenomycins and chemical and biological approaches to their derivatives are described. The biological properties of moenomycins and plausible mechanisms of bacterial resistance to them are also covered here, portraying a complete picture of the chemistry and biology of these fascinating natural products

BackgroundThe Streptomyces albus J1074 strain is one of the most widely used chassis for the heterologous production of bioactive natural products. The fast growth and an efficient genetic system make this strain an attractive model for expressing cryptic biosynthetic pathways to aid drug discovery.ResultsTo improve its capabilities for the heterologous expression of biosynthetic gene clusters, the complete genomic sequence of S. albus J1074 was obtained. With a size of 6,841,649 bp, coding for 5,832 genes, its genome is the smallest within the genus streptomycetes. Genome analysis revealed a strong tendency to reduce the number of genetic duplicates. The whole transcriptomes were sequenced at different time points to identify the early metabolic switch from the exponential to the stationary phase in S. albus J1074.ConclusionsS. albus J1074 carries the smallest genome among the completely sequenced species of the genus Streptomyces. The detailed genome and transcriptome analysis discloses its capability to serve as a premium host for the heterologous production of natural products. Moreover, the genome revealed 22 additional putative secondary metabolite gene clusters that reinforce the strain’s potential for natural product synthesis.

Pacidamycins are a family of uridyl tetra/pentapeptide antibiotics that act on the translocase MraY to block bacterial cell wall assembly. To elucidate the biosynthetic logic of pacidamcyins, a putative gene cluster was identified by 454 shotgun genome sequencing of the producer Streptomyces coeruleorubidus NRRL 18370. The 31-kb gene cluster encodes 22 proteins (PacA-V), including highly dissociated nonribosomal peptide synthetase (NRPS) modules and a variety of tailoring enzymes. Gene deletions confirmed that two NRPSs, PacP and PacO, are required for the biosynthesis of pacidamycins. Heterologous expression and in vitro assays of PacL, PacO, and PacP established reversible formation of m-Tyr-AMP, L-Ala-AMP, and diaminopropionyl-AMP, respectively, consistent with the amino acids found in pacidamycin scaffolds. The unusual Ala 4 -Phe 5 dipeptidyl ureido linkage was formed during in vitro assays containing purified PacL, PacJ, PacN, and PacO. Both the genetic and enzymatic studies validate identification of the biosynthetic genes for this subclass of uridyl peptide antibiotics and provide the basis for future mechanistic study of their biosynthesis.adenylation | ureido-bond | uridine P acidamycins are a family of uridyl tetra/pentapeptide antibiotics isolated from Streptomyces coeruleorubidus. Since their discovery in 1989, at least 10 related compounds have been reported (1, 2), which share a common structural skeleton with a 3′-deoxyuridine nucleoside attached to an N-methyl 2,3-diaminobutyric acid (DABA) residue via a 4′,5′-enamide linkage. Attached to the α-amino of DABA is L-Ala, which is linked to the C-terminal aromatic amino acid via a ureido linkage. An N-terminal amino acid or dipeptide is attached to the β-amino of DABA to give the tetra/pentapeptide framework (Fig. 1). Similar to many other uridyl peptides and uridyl lipopeptides, including liposidomycins (3), tunicamycins (4), capuramycins (5, 6), muraymycins (7), and more closely related mureidomycins (8) and napsamycins (9), pacidamycins exhibited antimicrobial activity targeting the translocase MraY to block formation of lipid I from UDP-N-acetylmuramoyl-pentapeptide and undecaprenyl phosphate during bacterial cell wall assembly (Fig. S1) (10, 11). The uracil-ribose moiety is a key determinant of binding to the MraY target (10).We have begun to focus on the biosynthesis of pacidamycin family uridyl peptide antibiotics due to their three unusual structural features (Fig. 1). The first one is the presence of the nonproteinogenic amino acids L-meta-tyrosine (L-m-Tyr) and DABA, which suggests that nonribosomal peptide synthetase (NRPS) modules might be involved in the tetra/pentapeptide framework formation. The second feature is that the peptide chain direction reverses twice during assembly. As exemplified in pacidamycin 1, the peptide bond between m-Tyr 2 and DABA 3 is a β-rather than an α-peptide linkage. Consequently, the DABA 3 -Ala 4 peptide bond uses the α-amino of DABA moiety and the chain is reversed at Ala 4 . Next, the attachment of that Al...

Peptidoglycan glycosyltransferases (PGTs), enzymes that catalyze the formation of the glycan chains of the bacterial cell wall, have tremendous potential as antibiotic targets. The moenomycins, a potent family of natural product antibiotics, are the only known active site inhibitors of the PGTs and serve as blueprints for the structure-based design of new antibacterials. A 2.8 Å structure of a Staphylococcus aureus PGT with moenomycin A bound in the active site appeared recently, potentially providing insight into substrate binding; however, the protein:ligand contacts were not analyzed in detail and the implications of the structure for inhibitor design were not addressed. We report here the 2.3 Å structure of a complex of neryl-moenomycin A bound to the PGT domain of Aquifex aeolicus PBP1A. The structure allows us to examine protein:ligand contacts in detail, and implies that six conserved active site residues contact the centrally-located F-ring phosphoglycerate portion of neryl-moenomycin A. A mutational analysis shows that all six residues play important roles in enzymatic activity. We suggest that small scaffolds that maintain these key contacts will serve as effective PGT inhibitors. To test this hypothesis, we have prepared, via heterologous expression of a subset of moenomycin biosynthetic genes, a novel moenomycin intermediate that maintains these six contacts but does not contain the putative minimal pharmacophore. This compound has comparable biological activity to the previously proposed minimal pharmacophore. The results reported here may facilitate the design of antibiotics targeted against peptidoglycan glycosyltransferases.

A 3 kb DNA fragment from the Streptomyces globisporus 1912 landomycin E (LaE) biosynthetic gene cluster (lnd) was completely sequenced. Three open reading frames were identified, lndGT4, lndZ4, and lndZ5, whose probable translation products resemble a glycosyltransferase, a reductase, and a hydroxylase, respectively. Studies of generated mutants from disruption and complementation experiments involving the lndGT4 gene allowed us to determine that LndGT4 controls the terminal L-rhodinose sugar attachment during LaE biosynthesis and that LndZ4/LndZ5 are responsible for the unique C11-hydroxylation of the landomycins. Generation of the novel landomycins F, G, and H in the course of these studies provided evidence for the flexibility of lnd glycosyltransferases toward their acceptor substrates and a basis for initial structure-activity relationships within the landomycin family of antibiotics.

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