Optimized genetic tools allow the biosynthesis of glycocin f and analogues designed to test the roles of gcc cluster genes in bacteriocin production

Abstract

The emergence of multidrug-resistant pathogens has motivated natural product research to inform the development of new antimicrobial agents. Glycocin F (GccF) is a diglycosylated 43-amino-acid bacteriocin secreted by Lactobacillus plantarum KW30. It displays a moderate phylogenetic target range that includes vancomycin- resistant strains of Enterococcus species and appears to have a novel bacteriostatic mechanism, rapidly inhibiting the growth of the most susceptible bacterial strains at picomolar concentrations. Experimental verification of the predicted role(s) of gcc cluster genes in GccF biosynthesis has been hampered by the inability to produce soluble recombinant Gcc proteins. Here, we report the development of pRV610gcc, an easily modifiable 11.2-kbp plasmid that enables the production of GccF in L. plantarum NC8. gcc gene expression relies on native promoters in the cloned cluster, and NC8(pRV610gcc) produces mature GccF at levels similar to KW30. Key findings are that the glycosyltransferase glycosylates both serine and cysteine at either position in the sequence but glycosylation of the loop serine is both sequence and spatially specific, that glycosylation of the peptide scaffold is not required for export and subsequent disulfide bond formation, that neither of the putative thioredoxin proteins is essential for peptide maturation, and that removal of the entire putative response regulator GccE decreases GccF production less than removal of the LytTR domain alone. Using this system, we have verified the functions of most of the gcc genes and have advanced our understanding of the roles of GccF structure in its maturation and antibacterial activity.