Bacterial hydrolytic dehalogenases and related enzymes: occurrences, reaction mechanisms, and applications

Dehalogenases catalyze the cleavage of the carbon-halogen bond of organohalogen compounds. They have been attracting a great deal of attention partly because of their potential applications in the chemical industry and bioremediation. In this personal account, we describe occurrences, reaction mechanisms, and applications of bacterial hydrolytic dehalogenases and related enzymes, particularly L-2-haloacid dehalogenase, DL-2-haloacid dehalogenase, fluoroacetate dehalogenase, and 2-haloacrylate reductase. L-2-Haloacid dehalogenase is a representative enzyme of the haloacid dehalogenase (HAD) superfamily, which includes the P-type ATPases and other hydrolases. Structural and mechanistic analyses of this enzyme have yielded important insights into the mode of action of the HAD superfamily proteins. Fluoroacetate dehalogenase is unique in that it catalyzes the cleavage of the highly stable C--F bond of a fluorinated aliphatic compound. In the reactions of L-2-haloacid dehalogenase and fluoroacetate dehalogenase, the carboxylate group of Asp performs a nucleophilic attack on the alpha-carbon atom of the substrate, displacing the halogen atom. This mechanism is common to haloalkane dehalogenase and 4-chlorobenzoyl-CoA dehalogenase. DL-2-Haloacid dehalogenase is unique in that a water molecule directly attacks the substrate, displacing the halogen atom. The occurrence of 2-haloacrylate reductase was recently reported, revealing a new pathway for the degradation of unsaturated aliphatic organohalogen compounds.