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Stereochemical course of cobalamin-dependent radical SAM methylation by TokK and ThnK† † Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d2cb00113f

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 TokK and ThnK. TokK and ThnK stereoselectively abstract the pro-S hydrogen, and methylation proceeds with inversion of absolute configuration at C6.

SUBMITTER: Lichstrahl M

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

REPOSITORIES: biostudies-literature

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