Stereochemical course of cobalamin-dependent radical SAM methylation by TokK and ThnK.

ABSTRACT: Complex carbapenems are important clinical antibiotics for difficult-to-treat infections. An essential step in the biosyntheses of these natural products is stereospecific methylation at C6 and subsequent alkylations by cobalamin-dependent radical SAM methylases such as TokK and ThnK. We have prepared isotopically labeled substrates in a stereospecific manner and found that both homologous enzymes selectively abstract the 6-pro-S hydrogen, followed by methyl transfer to the opposite face to give the (6R)-methyl carbapenam product proceeding, therefore, by inversion of absolute configuration at C6. These data clarify an unexpected ambiguity in the recently solved substrate-bound crystal structure of TokK and have led to a stereochemically complete mechanistic proposal for both

SUBMITTER: Lichstrahl MS 

PROVIDER: S-EPMC9358933 | biostudies-literature | 2022 Aug

REPOSITORIES: biostudies-literature