1 research outputs found
The B<sub>12</sub>-Radical SAM Enzyme PoyC Catalyzes Valine C<sub>β</sub>‑Methylation during Polytheonamide Biosynthesis
Genomic and metagenomic
investigations have recently led to the
delineation of a novel class of natural products called ribosomally
synthesized and post-translationally modified peptides (RiPPs). RiPPs
are ubiquitous among living organisms and include pharmaceutically
relevant compounds such as antibiotics and toxins. A prominent example
is polytheonamide A, which exhibits numerous post-translational modifications,
some of which were unknown in ribosomal peptides until recently. Among
these post-translational modifications, C-methylations have been proposed
to be catalyzed by two putative radical <i>S</i>-adenosylmethionine
(rSAM) enzymes, PoyB and PoyC. Here we report the <i>in vitro</i> activity of PoyC, the first B<sub>12</sub>-dependent rSAM enzyme
catalyzing peptide C<sub>β</sub>-methylation. We show that PoyC
catalyzes the formation of <i>S</i>-adenosylhomocysteine
and 5′-deoxyadenosine and the transfer of a methyl group to l-valine residue. In addition, we demonstrate for the first
time that B<sub>12</sub>-rSAM enzymes have a tightly bound MeCbl cofactor
that during catalysis transfers a methyl group originating from <i>S</i>-adenosyl-l-methionine. Collectively, our results
shed new light on polytheonamide biosynthesis and the large and emerging
family of B<sub>12</sub>-rSAM enzymes