Controlling Non-Native Cobalamin Reactivity and Catalysis in the Transcription Factor CarH
Xinhang Yang, Benjamin H. R. Gerroll, Yuhua Jiang, Amardeep Kumar, Yasmine S. Zubi, Lane A. Baker, Jared C. Lewis
Abstract
Vitamin B12 derivatives catalyze a wide range of organic transformations, but B12-dependent enzymes are underutilized in biocatalysis relative to other metalloenzymes. In this study, we engineered a variant of the transcription factor CarH, called CarH*, that catalyzes styrene C–H alkylation with improved yields (2–6.5-fold) and selectivity relative to cobalamin. While the native function of CarH involves transcription regulation via adenosylcobalamin (AdoCbl) Co(III)–carbon bond cleavage and β-hydride elimination to generate 4′,5′-didehydroadenosine, CarH*-catalyzed styrene alkylation proceeds via non-native oxidative addition and olefin addition coupled with a native-like β-hydride elimination. Mechanistic studies on this reaction echo findings from earlier studies on AdoCbl homolysis to suggest that CarH* selectivity results from its ability to impart a cage effect on radical intermediates. These findings lay the groundwork for the development of B12-dependent enzymes as catalysts for non-native transformations.