Total chemical synthesis of glycocin F and analogues: <i>S</i>-glycosylation confers improved antimicrobial activity

Abstract

Glycocin F (GccF) is a unique diglycosylated bacteriocin peptide that possesses potent and reversible bacteriostatic activity against a range of Gram-positive bacteria. GccF is a rare example of a 'glycoactive' bacteriocin, with both the <i>O</i>-linked <i>N</i>-acetylglucosamine (GlcNAc) and the unusual <i>S</i>-linked GlcNAc moiety important for antibacterial activity. In this report, glycocin F was successfully prepared using a native chemical ligation strategy and folded into its native structure. The chemically synthesised glycocin appeared to be slightly more active than the recombinant material produced from <i>Lactobacillus plantarum</i>. A second-generation synthetic strategy was used to prepare 2 site selective 'glyco-mutants' containing either two <i>S</i>-linked or two <i>O</i>-linked GlcNAc moieties; these mutants were used to probe the contribution of each type of glycosidic linkage to bacteriostatic activity. Replacing the <i>S</i>-linked GlcNAc at residue 43 with an <i>O</i>-linked GlcNAc decreased the antibacterial activity, while replacing <i>O</i>-linked GlcNAc at position 18 with an <i>S</i>-linked GlcNAc increased the bioactivity suggesting that the <i>S</i>-glycosidic linkage may offer a biologically-inspired route towards more active bacteriocins.