Bacitracins biosynthesis

Bacitracin biosynthesis requires a non-ribosomal peptide synthetase with three major protein components, BacABC. This synthetase has a modular structure. There are associated regulatory and transport systems. Biosynthesis of bacitracin has been engineered in the surrogate host, B. subtilis, by genetic techniques. A strain, B. subtilis KE 350, expresses the entire 49-kb bacitracin... 

Supek V, Gamulin S, Delic V. (1985) Enhancement of bacitracin biosynthesis by branched-chain amino acids in a regulatory mutant of Bacillus licheniformis. Folia Microbiol 30 342-348. 

The amino acids in bacitracin biosynthesis are activated as aminoacyl adenylates before being transferred to separate thiol sites on the synthetase (Ref. 31, 34). See Pig 4. 

PrszSyshov, Bacitracin biosynthesis by three conplementary frac-... 

Ishihara H. Shimura K. Further evidence for the presence of a thiazoline ring in the iso-leucylcysieine dipeptide intermediate in bacitracin biosynthesis. FEBS Lett 1988 226 319-323. 

Bernlohr, R. W., and G. D. Novelli Bacitracin biosynthesis and spore formation The physiological role of an antibiotic. Arch. Biochem. Biohpys. 103, 94 (1963). 

Bernlohr, R. W., and G. D. Novelli Bacitracin biosynthesis and spore formation. 

Bacitracin. Bacitracin, a cycHc peptide active against gram-positive bacteria, was discovered in 1943. Bacitracin received dmg certification in 1949 (60—62). Whereas human usage of bacitracin is almost exclusively topical, the vast majority of bacitracin manufactured worldwide is used as an animal feed additive. Reviews of work on bacitracin include its chemistry (63—67), comprehensive aspects (62), medical aspects (62,68), biosynthesis on large enzyme complexes and genetics (69—71), and production (71,72). 

Bacitracin (Fig. 4) is a cyclic peptide antibiotic. The lipid II molecule involved in the bacterial cell wall biosynthesis has a C55 isoprenyl pyrophosphate moiety that must be dephosphorylated so that it can reparticipate in another round of lipid II transfer. Bacitracin binds to the isoprenyl pyrophosphate and prevents the dephosphorylation which, in turn, blocks cell wall growth by interfering with the release of the muropeptide subunits to the outside of the bacterial cell membrane. Bacitracin inhibits similar reactions in eukaryotic cells. So, it is systemically toxic but is an effective and widely used topical antibiotic. 

Substances that interfere with the formation of polyprenyl phosphates are of 3 types (1) those that interfere with the biosynthesis of polyprenyl diphosphate for example, inhibitors of 3-hydroxy-3-meth-ylglutaryl-coenzyme A reductase (HMG-CoA reductase), (2) compounds that prevent the recycling of polyprenyl diphosphate (bacitracin), and (3) compounds that prevent the phosphorylation of... 

The biosynthesis of cell wall peptidoglycan, showing the sites of action of five antibiotics (shaded bars 1 = fosfomycin, 2 = cycloserine, 3 = bacitracin, 4 = vancomycin, 5 = 3-lactam antibiotics). Bactoprenol (BP) is the lipid membrane carrier that transports building blocks across the cytoplasmic membrane M, N-acetylmuramic acid Glc, glucose NAcGIc or G, /V-acetylglucosamine. 

The poly (ribitol phosphate) synthetase and poly (glycerol phosphate) synthetase are inhibited by vancomycin, novobiocin, and Crystal Violet. Other antibiotic substances which interfere with cell-wall synthesis (such as bacitracin, ristocetin, and streptomycin) are almost without effect on the isolated synthetases, and penicillin is inhibitory at high concentrations only. Moreover, penicillin, vancomycin, and bacitracin do not markedly inhibit synthesis of cell-wall glycosaminopeptide in vitro, although the synthetical activity of extracts of cells which have been pretreated with these antibiotics is lowered.Convincing evidence that the primary site of inhibition by antibiotics is the biosynthesis of cell-wall material has been obtained only for the penicillins and cycloserine, and it appears that the action of even those antibiotics may be more complex than was originally supposed. 

Quadri LE, Sello J, Keating TA, Weinreb PH, Walsh CT. Identification of a Mycobacterium tuberculosis gene cluster encoding the biosynthetic enzymes for assembly of the virulence-conferring siderophore mycobactin. Chem. Biol. 1998 5 631-645. Eppelmann K, Doekel S, Marahiel MA. Engineered biosynthesis of the peptide antibiotic bacitracin in the surrogate host Bacillus subtiUs. J. Biol. Chem. 2001 276 34824-34831. 

Bacitracin is a mixture of similar peptides produced by fermentation of the bacterium Bacillus subtilis. The A-type component predominates. Its mode of action is to inhibit both peptidoglycan biosynthesis at a late stage (probably at the dephosphorylation of the phospholipid carrier step) and disruptions of plasma membrane function. It is predominantly active against Gram-positive microorganisms, and parenteral use is limited to IM injection for infants with pneumonia and empyema caused by staphylococci resistant to other agents. It is rather neuro- and nephrotoxic and, therefore, is used in this manner with caution. Bacitracin also is widely employed topically to prevent infection in minor cuts, scrapes, and burns. 

Herscovics, A., Bugge, B. Jeanloz, R.W. (1977) Effect of Bacitracin on the Biosynthesis of Dolichol Derivatives in Calf Pancreas Microsomes, FEBS Letters, 82, 215-8... 

The end-product repression involves probably the blockage of formation of specific synthases, at the time of a maximum rate of secondary biosynthesis. This results in a gradual decline in the level of the enzyme and a retardation of the product formation. The phenomenon was observed in gramicidin S synthases by Bacillus brevis (30), bacitracin synthase in Bacillus licheniformis (31), anhydrotetracycline hydratase by treptomyces aureofaci-ens (4), novobiocic acid synthase in Streptomyces niveus (35) or dimethylallyltryptophan synthase by ciaviceps (33). 

As a model system we would like to describe the biosynthesis of bacitracin, a commercially important peptide antibiotic. Its mechanism of formation has been studied in our laboratory as well as by others. A cell free system for bacitracin production by B. Hcheniformis ATCC 10716 was reported by Ishihara et al.(29). The methods used were modified (Ref. 31) and a partially purified enzyme complex which performed de novo synthesis of bacitracin from the L-isomers of the constituent amino acids, ATP and Mg2 was isolated (Ref. 31 - 34). D-glutamic acid and D-phenylala-nine which occur in bacitracin support its synthesis (Ref. 31). This was also the case for D-aspartic acid (unpublished results). 

All the enzymes of bacitracin synthetase contain the cofactor phosphopantetheine which probably acts as a covalently linked carrier of intermediates in the biosynthesis of bacitracin (Ref. 36, 37). 

Regulation of secondary metabolites by glucose or ocher easily assimilated carbon sources (glucose repression) occurs in the biosynthesis of several antibiotics (penicillin, aciinomycin, streptomycin, siomycin, bacitracin, etc.) (fora review, see Refs. 89 and 90), but not in the biosynthesis of polyene antibiotics, because glucose is required for their biosynthesis. 

Suppression by excess nutrients has been found in the biosynthesis of polyketides (D 3.3), of gibberellins (D 6.3), of certain antibiotics, e.g., streptomycin (D 1.3), neomycin C (D 1.3), actinomycins (D 8.4.1), chloramphenicol (D 8.2), bacitracin A (D 23), enniatin B (D 23), cephalosporins (D 23.3), and penicillins (D 23.3), of alkaloids, e.g., benzodiazepines (D 8.4.2), and ergolines (D 21.2) etc. Usually the suppression of secondary product formation is accompanied by the suppression of other characteristics of cell specialization (such as conidiospore formation in Peni-cillium cyclopium), indicating a general influence of nutrient supply on cell specialization. 

Recent work on the structure and biosynthesis of bacterial cell walls has given some indication of the way in which the crosslinked polysaccharide components are formed. There are several justifications for including here a brief account of work in this field. Firstly, certain antibiotics (e.g. the penicillins, bacitracin A, novabiocin) are known specifically to inhibit bacterial cell-wall synthesis. If, as seems likely, the inhibition is of an enzyme-catalysed reaction, a knowledge of the particular substrates involved might lead to the design of more powerful bactericidal agents. Secondly, the particular type of cell... 

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