The Expanding Reactivity of Cobamide-Containing Proteins: From Mechanistic Understanding to Non-native Biocatalysis.

Cobamides are tetrapyrrole cofactors whose core structure, diverse axial ligands, and ability to access distinct redox states underpin the reactivity of a variety of enzymes, including isomerases, methyltransferases, and reductive dehalogenases. These enzymes leverage precise scaffold-controlled interactions to direct radical rearrangement, methyl group transfer, and reductive bond cleavage with high selectivity and efficiency. Despite these capabilities, the native reactivity of cobamide-dependent enzymes remains relatively underutilized for biocatalysis, and their use as catalysts for non-native reactions has only recently emerged as a promising frontier. Mechanistic studies and advances in protein engineering and synthetic biology are beginning to establish these enzymes and other cobamide-containing proteins as versatile platforms for selective C-C bond formation, C-H functionalization, alkylation, and other transformations. This perspective summarizes key mechanistic aspects of cobamide-containing protein function, highlights progress in native biocatalysis and discusses emerging strategies to exploit cobamide-containing proteins for non-native biocatalysis.