Cobalamin-dependent dehydratases and a deaminase: Radical catalysis and reactivating chaperones

•X-ray structures of cobalamin radical enzymes catalyzing eliminations were solved.•Structure-based refined mechanisms explain the experimental results reported to date.•Radical catalysis of a cobalamin enzyme is supported by theoretical calculations.•Chaperones reactivate cobalamin radical enzymes by releasing damaged cofactors.•Radical status of cobalamin enzymes is maintained by coenzyme recycling systems.

Adenosylcobalamin, a coenzyme form of vitamin B12, is an organometallic compound that participates in about ten enzymatic reactions. These enzymes catalyze chemically challenging reactions by using a highly reactive primary carbon radical that is derived from homolysis of the coenzyme Co–C bond. Among them, diol dehydratases and ethanolamine ammonia-lyase have been most extensively studied to establish the general mechanism of adenosylcobalamin-assisted enzymatic catalysis and radical-catalyzed reactions. Another important point is that adenosylcobalamin-dependent radical enzymes are prone to mechanism-based irreversible inactivation during catalysis and have their own chaperones for the maintenance of catalytic activities. This review will highlight biochemical, structural, and computational studies with special emphases on radical catalysis and reactivating chaperones of these enzymes.

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