Methylene Peptide Backbone Substitution Significantly Affects the Glycopeptide Antibiotic Cross-Linking Cascade

Glycopeptide antibiotics (GPAs) are clinically important antibiotics characterized by a rigid, highly cross-linked structure. The cross-links in GPAs are installed by the activity of several cytochrome P450 (Oxy) enzymes, which are recruited to their peptide substrates by a unique domain, the X-domain. Given that this cross-linking cascade is the source of both the antibiotic activity and the synthetic complexity of GPAs, it remains a central point for exploring the tolerance of the Oxy enzymes for altered peptide substrates. In this study, we have investigated the ability of the Oxy enzymes to cross-link peptides with changes to their amide backbone, specifically a [Ψ[CH₂NH]Tpg] methylene linkage that was inspired by synthetic efforts showing that such analogues can recover antibiotic activity toward resistant bacteria. Our results show that the Oxy enzymes are extremely sensitive to the presence of a methylene linkage in their peptide substrates, which suggests that these backbone carbonyl groups play a crucial role in maintaining the correct binding of peptide substrates to the P450 enzymes within the GPA cross-linking cascade.