# Synthesis and Antimicrobial Specificities of Halogenated Tryptophan-Containing Nisin Variants

## TL;DR

This study explores how adding halogenated tryptophan to a bacterial peptide can change its antimicrobial activity against different pathogens.

## Contribution

A new method for incorporating halogenated tryptophan into antimicrobial peptides using a tryptophan auxotrophic Lactococcus lactis strain is demonstrated.

## Key findings

- Halogenated tryptophan analogues were successfully incorporated into nisin A at position 1.
- The modified nisin variants showed strain-specific antimicrobial activity against tested pathogens.
- No clear correlation was found between halogen properties and antimicrobial efficacy.

## Abstract

Antimicrobial peptides,
and in particular ribosomally
produced
and post-translationally modified peptides (RiPPs), are a potentially
important class of candidate antibiotics for combating multidrug-resistant
bacteria. Introduction of a halogenated Trp residue into a RiPP can
possibly enhance antimicrobial efficacy and alter specificity, but
this modification has hardly been explored. This study employs an
efficient expression system utilizing a tryptophan auxotrophic Lactococcus lactis strain to biosynthetically and
efficiently incorporate halogenated tryptophan analogues, namely 5-fluoro-tryptophan
(5FW), 5-chloro-tryptophan (5CW), 5-bromo-tryptophan (5BW), as well
as 5-methyl-tryptophan (5MW) at position 1 of I1W nisin A. Wild-type
nisin and Trp-containing I1W nisin show a high and broad activity
against four tested pathogens. However, the activity spectrum of the
three different halogen atom containing nisin variants became more
strain specific, as both increased and decreased activities were measured
against the four tested pathogens. No trend between the chemical properties
of the halogen atom (e.g., electronegativity, size) and the bioactivity
of the nisin variants toward each of the four pathogens could be detected,
suggesting strain specific antimicrobial activity mechanisms. These
findings demonstrate that halogenated tryptophan analogues can be
successfully incorporated into a bioactive RiPP produced by an auxotrophic L. lactis strain and underscore the utility of peptide
halogenation for discovering novel antimicrobial agents with tailored
pathogen specificity.