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Halogenation is a frequent modification of secondary metabolites and can play a significant role in establishing the bioactivity of a compound. Enzymatic halogenation through oxidative mechanisms is the most common route to these metabolites, though direct halogenation via halide anion incorporation is also known to proceed through both enzymatic and nonenzymatic pathways. In this article, we review the current state of knowledge regarding the mechanisms of these transformations, highlight applications of this knowledge, and propose future opportunities and challenges for the field. [Copyright &y& Elsevier]

Summary: Chlorinated compounds are important environmental pollutants whose biodegradation may be limited by inefficient dechlorinating enzymes. Dictyostelium amoebae produce a chlorinated alkyl phenone called DIF which induces stalk cell differentiation during their multicellular development. Here we describe the identification of DIF dechlorinase. DIF dechlorinase is active when expressed in bacteria, and activity is lost from Dictyostelium cells when its gene, drcA, is knocked out. It has a Km for DIF of 88 nM and Kcat of 6.7 s−1. DrcA is related to glutathione S-transferases, but with a key asparagine-to-cysteine substitution in the catalytic pocket. When this change is reversed, the enzyme reverts to a glutathione S-transferase, thus suggesting a catalytic mechanism. DrcA offers new possibilities for the rational design of bioremediation strategies. [ABSTRACT FROM AUTHOR]