Mechanistic Investigations of Lysine-Tryptophan Cross-Link Formation Catalyzed by Streptococcal Radical S-Adenosylmethionine Enzymes.

TitleMechanistic Investigations of Lysine-Tryptophan Cross-Link Formation Catalyzed by Streptococcal Radical S-Adenosylmethionine Enzymes.
Publication TypeJournal Article
Year of Publication2018
AuthorsSchramma, KR, Forneris, CC, Caruso, A, Seyedsayamdost, MR
JournalBiochemistry
Volume57
Issue4
Pagination461-468
Date Published2018 Jan 30
ISSN1520-4995
Abstract

Streptide is a ribosomally synthesized and post-translationally modified peptide with a unique cyclization motif consisting of an intramolecular lysine-tryptophan cross-link. Three radical S-adenosylmethionine enzymes, StrB, AgaB, and SuiB from different species of Streptococcus, have been shown to install this modification onto their respective precursor peptides in a leader-dependent fashion. Herein, we conduct detailed investigations to differentiate among several plausible mechanistic proposals, specifically addressing radical versus electrophilic addition to the indole during cross-link formation, the role of substrate side chains in binding in the enzyme active site, and the identity of the catalytic base in the reaction cycle. Our results are consistent with a radical electrophilic aromatic substitution mechanism for the key carbon-carbon bond-forming step. They also elaborate on other mechanistic features that underpin this unique and synthetically challenging post-translational modification.

DOI10.1021/acs.biochem.7b01147
Alternate JournalBiochemistry
PubMed ID29320164