Daptomycin biosynthesis

Miao, V., Coeffet-Le Gal M.-F. et al. (2005) Daptomycin biosynthesis in Streptomyces roseosporus cloning and analysis of the gene cluster and revision of peptide stereochemistry. Microbiology (Reading, England), 151,1507. 

Nguyen, K.T., Kau, D., Gu, J.Q. et al. (2006) A glutamic acid 3-methyltransferase encoded by an accessory gene locus important for daptomycin biosynthesis in Streptomyces roseosporus. Molecular Microbiology, 61 (5), 1294-1307. 

The location (in base pairs) of the giant dptA, dptBC and dptD genes cloned on BAC pVCl which contains a 128 000 base pair insert.14 The dptA, dptBC and dptD genes encode five, six and two modules, respectively. The specificity of A domains is shown with amino acid subscripts. The C condensation domain differs from the others in that it couples the long chain fatty acids to the TV-terminus of Trp i to initiate daptomycin biosynthesis. Note that modules 2, 8 and 11 have CATE modules to incorporate D-amino acids. The Kyn13 module has a terminal Te (as CATTe) to cyclise and release the completed lipopeptide. 

Most of the latest publications on NRPS substrate specificity are focused on A domain specificity because their substrate screening is straightforward in terms of biosynthetic substrate form (free amino acids/fatty acids/aryl acids) and T domain substrates (one T domain). Four studies focus on substrate specificity of NRPS loading modules of microcystin biosynthesis,97 mycosubtilin biosynthesis,51 daptomycin biosynthesis,108 and leinamycin biosynthesis.108 The A domains of microcystin, mycosubtilin, and daptomycin biosynthesis initiation showed fatty acid specificity. The initial domain from leinamycin biosynthesis has D-amino acid specificity. Another paper presents the elucidation of aryl acid-specific AsbC adenylation enzyme from petrobactin biosynthesis.104... 

The recent studies of Hansen et al51 and Wittmann et al,109 revealed a new mechanism for lipidation of lipopeptide biosynthesis such as mycosubtilin or daptomycin biosynthesis by application of ESI-FTMS. Both papers describe that fatty acid incorporation is catalyzed by an A domain with fatty acid specificity in the loading module of the mycosubtilin NRPS (Figure 15) or by a preassembly line A and T domain in daptomycin biosynthesis (Figure 16). 

These data are consistent with a second possible mechanism of action of daptomycin inhibition of YycG function in S. aureus and perhaps in some other low G + C Gram-positive bacteria, but not in E. coli or other Gramnegative bacteria which lack this target. This model is also consistent with the early studies showing that daptomycin inhibits cell wall biosynthesis at an unspecified early step(s).24 This partial mechanism of action is consistent with daptomycin synergy with gentamicin and certain (1-lactam antibiotics (see below). 

Nguyen KT, Ritz D, Gu JQ, Alexander D, Chu M, Miao V, Brian P, Baltz RH (2006) Combinatorial Biosynthesis of Novel Antibiotics Related to Daptomycin. Proc Natl Acad Sci USA 103 17462... 

If the primary mechanism of daptomycin bactericidal activity is dissipation of membrane function that indirectly influences peptidoglycan, C A, RHA, protein, lipid, and teichoic acid biosynthesis, it is not clear why daptomycin is synergistic with aminoglycosides. Uptake and bactericidal activity of aminoglycosides require membrane potential (72,73). 

Canepari et al. (74) have shown that at the MIC, daptomycin caused only partial blockage of DNA, RNA, protein, and peptidoglycan biosynthesis in . faecium. In contrast, it caused >50% inhibition of radiolabeled phosphate into teichoic acid and >90% inhibition of incorporation of radiolabeled glycerol into lipoteichoic acid in 20 min in both S. aureus and in . faecium. They also showed that daptomycin does not penetrate bacterial cells, but binds reversibly to cell walls and irreversibly to cell membrane in the... 

In another study, Boaretti et al, (75) have shown that daptomycin at the MIC in the presence of causes inhibition of protoplast regeneration in H. faedum, whereas vancomycin does not. They showed that daptomycin caused 82% inhibition of lipotei-choic acid biosynthesis in E. faedum protoplasts, 40% inhibition of lipid biosynthesis, and only 14, 17, and 23% inhibition of peptidoglycan, DNA, and protein biosynthesis, respectively. They demonstrated Ca -dependent tight binding of daptomycin to the cytoplasmic membrane. These data are consistent with the notion that lipoteichoic acid biosynthesis is the primary target of daptomycin at low concentrations. 

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