Bacteriocins are ribosomally-synthesised bacterial peptides that inhibit the growth of closely-related strains or species of bacteria. Glycocin F (GccF) is a glycosylated, 43 amino acid bacteriocin (glycocin) produced by a strain of the probiotic bacteria Lactobacillus plantarum. It is modified by two N-acetylglucosamine (GlcNAc) moieties that are essential for its antibacterial activity. Whereas most bacteriocins exhibit bactericidal effects on a narrow range of species, GccF displays potent and reversible bacteriostatic activity towards a range of Gram positive bacteria, and at least one Gram negative bacterium, and so may be useful in combating antibiotic resistant bacteria. Although progress has been made on the identification of the GccF receptor in target cells, the inhibitory mechanism of GccF remains to be elucidated.
The recent development of a complete chemical synthesis scheme for GccF enabled the production of GccF variants, not accessible by other routes, to probe structure-activity relationships, including the nature of the GccF-receptor interaction. Bioassays were carried out with these GccF variants using a susceptible strain of L. plantarum. Modifications to wild-type GccF included changing the glycosylated amino acids, introducing steric modifiers around the ɑ-carbon of one of the glycosylated residues, shortening the flexible tail and removing each of the disulfide bonds. The results of these experiments will be presented and discussed in terms of the possible mechanisms of GccF-mediated bacteriostasis.