First and Second Sphere Interactions Accelerate Non-Native N-Alkylation Catalysis by the Thermostable, Methanol-Tolerant B12-Dependent Enzyme MtaC

During efforts to explore the range of reactions catalyzed by the previously-engineered B12-dependent enzyme CarH*, we found that this enzyme catalyzes N-alkylation of aniline using ethyl diazoacetate but that B12 itself provides only trace conversion for this reaction. This observation suggested that the unique primary and second coordination sphere provided by CarH* accelerates non-native N-alkylation catalysis and that other B12-dependent proteins could provide further improvements in activity. We used a structural homology search to identify the corrinoid protein MtaC, which was reconstituted with B12 to generate a catalyst with significantly-improved aniline N-alkylation activity on a range of substrates. MtaC also displays remarkable thermal stability and organic solvent tolerance, remaining folded even in pure methanol. These results highlight how protein scaffolds can be used to impart new activity and other beneficial properties to metal catalysts and suggest that MtaC could serve as a useful platform for non-native B12 catalysis.