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The X-ray structure of cis-3-chloroacrylic acid dehalogenase (cis-CaaD) with a sulfate ion bound in the active site
Structural highlights
FunctionEvolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe bacterial degradation pathways for the nematocide 1,3-dichloropropene rely on hydrolytic dehalogenation reactions catalyzed by cis- and trans-3-chloroacrylic acid dehalogenases (cis-CaaD and CaaD, respectively). X-ray crystal structures of native cis-CaaD and cis-CaaD inactivated by (R)-oxirane-2-carboxylate were elucidated. They locate four known catalytic residues (Pro-1, Arg-70, Arg-73, and Glu-114) and two previously unknown, potential catalytic residues (His-28 and Tyr-103'). The Y103F and H28A mutants of these latter two residues displayed reductions in cis-CaaD activity confirming their importance in catalysis. The structure of the inactivated enzyme shows covalent modification of the Pro-1 nitrogen atom by (R)-2-hydroxypropanoate at the C3 position. The interactions in the complex implicate Arg-70 or a water molecule bound to Arg-70 as the proton donor for the epoxide ring-opening reaction and Arg-73 and His-28 as primary binding contacts for the carboxylate group. This proposed binding mode places the (R)-enantiomer, but not the (S)-enantiomer, in position to covalently modify Pro-1. The absence of His-28 (or an equivalent) in CaaD could account for the fact that CaaD is not inactivated by either enantiomer. The cis-CaaD structures support a mechanism in which Glu-114 and Tyr-103' activate a water molecule for addition to C3 of the substrate and His-28, Arg-70, and Arg-73 interact with the C1 carboxylate group to assist in substrate binding and polarization. Pro-1 provides a proton at C2. The involvement of His-28 and Tyr-103' distinguishes the cis-CaaD mechanism from the otherwise parallel CaaD mechanism. The two mechanisms probably evolved independently as the result of an early gene duplication of a common ancestor. Crystal structures of native and inactivated cis-3-chloroacrylic acid dehalogenase. Structural basis for substrate specificity and inactivation by (R)-oxirane-2-carboxylate.,de Jong RM, Bazzacco P, Poelarends GJ, Johnson WH Jr, Kim YJ, Burks EA, Serrano H, Thunnissen AM, Whitman CP, Dijkstra BW J Biol Chem. 2007 Jan 26;282(4):2440-9. Epub 2006 Nov 22. PMID:17121835[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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