Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 141, Issue 42, Pages 16790-16801Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.9b07396
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Funding
- National Institutes of Health [R37 GM058822, F32 GM117765]
- Natural Sciences and Engineering Research Council of Canada (NSERC)
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Lanthipeptides represent a large class of cyclic natural products defined by the presence of lanthionine (Lan) and methyllanthionine (MeLan) cross-links. With the advances in DNA sequencing technologies and genome mining tools, new biosynthetic enzymes capable of installing unusual structural features are continuously being discovered. In this study, we investigated an O-methyltransferase that is a member of the most prominent auxiliary enzyme family associated with class I lanthipeptide biosynthetic gene clusters. Despite the prevalence of these enzymes, their function has not been established. Herein, we demonstrate that the O-methyltransferase OlvS(A) encoded in the olv gene cluster from Streptomyces olivaceus NRRL B-3009 catalyzes the rearrange- ment of a highly conserved aspartate residue to a beta-amino acid, isoaspartate, in the lanthipeptide OlvA(BCSA). We elucidated the NMR solution structure of the GluC-digested peptide, OlvA(BCSA)(GluC), which revealed a unique ring topology comprising four interlocking rings and positions the isoaspartate residue in a solvent exposed loop that is stabilized by a MeLan ring. Gas chromatography-mass spectrometry analysis further indicated that OlvA(BCSA) contains two DL-MeLan rings and two Lan rings with an unusual LL-stereochemistry. Lastly, in vitro reconstitution of OlvS, activity showed that it is a leader peptide-independent and S-adenosyl methionine-dependent O-methyltransferase that mediates the conversion of a highly conserved aspartate residue in a cyclic substrate into a succinimide, which is hydrolyzed to generate an Asp or isoAsp containing peptide. This overall transformation converts an alpha-amino acid into a beta-amino acid in a ribosomally synthesized peptide, via an electrophilic intermediate that may be the intended product.
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