Nonnative Thiol and Aniline Methylation, Including Enantioselective Dithiol Desymmetrization, by Multicomponent Cobamide‐Dependent Methyltransferases Using Unactivated Methyl Donors

Despite their potential synthetic utility, cobamide‐dependent MTases are relatively underutilized for biocatalysis. We developed mixed MtaABC/MtgABC enzyme platforms capable of catalyzing methylation of non‐native thiol and aniline substrates using unactivated methyl donors like methanol and glycine betaine. This approach allows highly enantioselective and site‐selective methylation of aliphatic thiols with high turnover number (up to 6000), providing the first demonstration of enantioselective non‐native catalysis by cobamide‐dependent enzymes. The MtaAC+MtgB system was subsequently engineered through site‐directed mutagenesis, resulting in large enhancements in activity for the desymmetrization of non‐native ester‐containing prochiral thiols. These findings establish MTase complexes as a promising platform for non‐native biocatalysis.