4-Chlorobenzoyl-CoA dehalogenase

Scheme 10.32 Examples of reactions catalyzed by different classes of dehalogenases. HD haloalcohol dehalogenase EH epoxide hydrolase CL p-chlorobenzoyl-CoA ligase CBD p-chlorobenzoyl-CoA dehalogenase.

Chlorobenzoyl-CoA dehalogenase. The enzymatic release of chloride ion from 4-chloroxybenzoyl-CoA... 

In fact, close sequence and structural homologies show that chlorobenzoyl-CoA dehalogenase, enoyl-CoA hydratase, and a variety of other hydratases, isomerases, synthases, lyases, and hydrolases belong to a large family of related proteins 49a 49b/49c... 

However, 4-chlorobenzoyl-CoA dehalogenase is also a member of the enoyl-CoA hydratase superfamily. The mechanism of its reaction involves nucleophilic aromatic substitution in which an active site Asp adds to the 4-position of the benzoyl ring to necessarily form a Meisenheimer complex this Meisenheimer complex is an analog of a thioester enolate anion. Although the Meisenheimer complex cannot be observed for displacement of chloride from 4-chlorobenzoyl-CoA due to the rate constants for formation and decomposition of the intermediate, the Meisen-... 

Chlorobenzoyl-CoA dehalogenase EC 3.8.1.7 Exchange of Cl for OH on 4-position of aromatic ring... 

ECH or crotonase is the prototypical member of the crotonase superfamily. As noted above, sequence homology between ECH and 3,2-enoyl-CoA isomerase as well as with dibydroxynapbtboate syntbase (MenB) and 4-chlorobenzoyl-CoA dehalogenase resulted in the initial proposal for a superfamily based on the crotonase scaffold. Since then, many more members of the superfamily have been identified. Most family members utilize substrates that are CoA thioesters, and a unifying mechanistic theme throughout the superfamily concerns the use of an oxyanion hole to stabilize carbanionic transition states. Figure 40 shows the reactions catalyzed by a subset of family members. ... 

Two mitochondrial isoforms of rat A A -enoyl-CoA isomerase have been described, the first one being a mitochondrial short-chain isomerase with a preferred chain-length specificity of Cg-C. This heat-stable enzyme has a subunit size of 30kDa and a pi value of about 9.5. The second isoform found in rat liver is also mitochondrial, but its catalytic rate is greatest for Cjo-Cn enoyl-CoA substrates and it is not clofibrate-inducible, unlike the rat liver short-ehain specific enzyme. The cDNA sequence of the mitochondrial short-chain isomerase has been published and its amino acid sequence shows similarity to the mitochondrial 2-enoyl-CoA hydratase 1. Currently the hydratase/isomerase family has about 30 known eukaryotic and prokaryotic members and the structure for two members has been published (rat mitochondrial 2-enoyl-CoA hydratase 1 and Pseudomonas sp. 4-chlorobenzoyl-CoA dehalogenase ). They all possess a conserved fingerprint of Val-Ser-X-Ile-Asn-Qy-X-X-X-Ala-Gly-Qy-X-Leu-X-X-X-X-Cys-Asp-Tyr, potentially have similar main chain folding, and catalyze reactions with carboxylic CoA esters as substrates. "... 

Previous studies on other bacterial hydrolytic dehalogenases have revealed different mechanisms and structures. High resolution X-ray structures of haloalkane dehalogenase(iO), 4-chlorobenzoyl CoA dehalogenase 31) and L-2-haloacid dehalogenase (52) revealed that these enzymes use an active site aspartate in nucleophilic displacement of the chlorine substituent as chloride anion. The enzyme-substrate ester intermediate is subsequently hydrolyzed by... 

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