NATURAL PEPTIDES WITH ANTIMICROBIAL ACTIVITY

Antibiosis is a mechanism by which many cell types control potential e nvironmental takeover or pathogenicity by microbes, especially bacteri a. It is now clear that a large proportion of the antimicrobial compou nds produced by various cells and organisms including bacteria, fungi, plants, insects, amphibia and mammals are antibiotics based around pe ptides. These antimicrobial peptides can be broadly subdivided into tw o groups: those which are produced by multienzyme complexes and those which are encoded by a structural gene, the transcription and translat ion of which results in a peptide template which may (in some cases) u ndergo further enzymatic modifications. In this context, the chemistry , biosynthesis and functional aspects of a broad range of bioactive pe ptides from both subgroups will be briefly discussed, including: grami cidin, bacitracin, valinomycin, alamethicin and polymixin B from the f irst group, and defensins (and related peptides), bacteriocins, lantib iotics and microcins from the second subgroup. From a biotechnological perspective, the peptide antibiotics produced by multienzyme complexe s are open to a variety of manipulations to produce novel antibiotic c ompounds, whilst the ribosomally synthesised peptides may be specifica lly altered by site-directed mutagenesis. Furthermore, the enzymes cap able of transforming some ribosomally synthesised peptide antibiotics may be of particular interest to the biotechnologist, because of the n ovel transformations of peptide substrates which they are able to perf orm.