Radical Approach to Enzymatic β-Thioether Bond Formation

Area of Science:

• Biochemistry
• Natural Products Chemistry
• Enzymology

Background:

• Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a diverse class of natural products.
• Tailoring enzymes introduce unique chemical functionalities to RiPPs.
• Unusual metalloenzymes in RiPP gene clusters may lead to novel modifications.

Purpose of the Study:

• Investigate unexplored RiPP gene clusters containing uncharacterized radical S-adenosylmethionine (RaS) metalloenzymes.
• Characterize the catalytic activity of a novel RaS enzyme, NxxcB.
• Identify new peptide macrocyclization strategies and expand the RaS enzyme superfamily's repertoire.

Main Methods:

• Bioinformatic search strategy to identify RiPP gene clusters.
• Biochemical investigation of RaS enzyme activity.
• Substrate analysis to determine enzyme specificity.

Main Results:

• Identified quorum sensing-regulated RiPP gene clusters with uncharacterized RaS metalloenzymes.
• NxxcB installs an intramolecular β-thioether bond by linking a Cys-thiol to the β-carbon of an Asn residue.
• NxxcB accepts various amino acids, creating unnatural β-thioether linkages at unactivated positions.

Conclusions:

• Discovered a novel β-thioether bond formation catalyzed by the RaS enzyme NxxcB.
• This finding expands the known peptide macrocyclization strategies.
• Demonstrates the significant catalytic versatility of the RaS enzyme superfamily.