Synthesis and Antimicrobial Specificities of Halogenated Tryptophan-Containing Nisin Variants

Area of Science:

• Biochemistry
• Microbiology
• Synthetic Biology

Background:

• Ribosomally produced and post-translationally modified peptides (RiPPs) are a promising class of antibiotics for combating multidrug-resistant bacteria.
• Modifying RiPPs, such as nisin, with halogenated tryptophan residues could potentially enhance antimicrobial efficacy and specificity.
• The incorporation of halogenated tryptophan analogues into RiPPs has been underexplored.

Purpose of the Study:

• To biosynthetically incorporate halogenated tryptophan analogues (5-fluoro-, 5-chloro-, 5-bromo-tryptophan) into the RiPP nisin A at position 1 using a tryptophan auxotrophic Lactococcus lactis strain.
• To evaluate the antimicrobial activity and specificity of the resulting halogenated nisin variants against selected pathogens.
• To explore the relationship between the chemical properties of halogen substituents and the antimicrobial bioactivity.

Main Methods:

• Utilized a tryptophan auxotrophic Lactococcus lactis strain for efficient biosynthesis of modified nisin.
• Incorporated 5-fluoro-tryptophan (5FW), 5-chloro-tryptophan (5CW), 5-bromo-tryptophan (5BW), and 5-methyl-tryptophan (5MW) into nisin A at position 1.
• Assessed the antimicrobial activity of wild-type nisin, I1W nisin, and halogenated nisin variants against four different bacterial pathogens.

Main Results:

• Successful incorporation of halogenated tryptophan analogues into nisin A was achieved.
• Wild-type and non-halogenated I1W nisin exhibited broad-spectrum activity.
• Halogenated nisin variants displayed altered and strain-specific activity profiles, with both increased and decreased efficacy observed.
• No clear correlation was found between halogen properties (electronegativity, size) and antimicrobial activity, suggesting complex strain-specific mechanisms.

Conclusions:

• Halogenated tryptophan analogues can be successfully incorporated into bioactive RiPPs using an auxotrophic L. lactis expression system.
• Peptide halogenation is a viable strategy for discovering novel antimicrobial agents with potentially tailored pathogen specificity.
• The observed strain-specific activity highlights the complexity of RiPP-pathogen interactions and the potential for fine-tuning antimicrobial properties through targeted modifications.