Facile Halogenation of Antimicrobial Peptides As Demonstrated by Producing Bromotryptophan-Labeled Nisin Variants with Enhanced Antimicrobial Activity

Antimicrobial peptides (AMPs) have raised significant interest, forming a potential new class of antibiotics in the fight against multi-drug-resistant bacteria. Various AMPs are ribosomally synthesized and post-translationally modified peptides (RiPPs). One post-translational modification found in AMPs is the halogenation of Trp residues. This modification has, for example, been shown to be critical for the activity of the potent AMP NAI-107 from Actinoallomurus. Due to the importance of organohalogens, establishing methods for facile and selective halogen atom installation into AMPs is highly desirable. In this study, we introduce an expression system utilizing the food-grade strain Lactococcus lactis, facilitating the efficient incorporation of bromo-Trp (BrTrp) into (modified) peptides, exemplified by the lantibiotic nisin with a single Trp residue or analogue incorporated at position 1. This provides an alternative to the challenges posed by halogenase enzymes, such as poor substrate selectivity. Our method yields expression levels comparable to that of wild-type nisin, while BrTrp incorporation does not interfere with the post-translational modifications of nisin (dehydration and cyclization). One brominated nisin variant exhibits a 2-fold improvement in antimicrobial activity against two tested pathogens, including a WHO priority pathogen, while maintaining the same lipid II binding and bactericidal activity as wild-type nisin. The work presented here demonstrates the potential of this methodology for peptide halogenation, offering a new avenue for the development of diverse antimicrobial products labeled with BrTrp.