The X-ray structure of trans-3-chloroacrylic acid dehalogenase reveals a novel hydration mechanism in the tautomerase superfamily

J Biol Chem. 2004 Mar 19;279(12):11546-52. doi: 10.1074/jbc.M311966200. Epub 2003 Dec 29.

Abstract

Isomer-specific 3-chloroacrylic acid dehalogenases function in the bacterial degradation of 1,3-dichloropropene, a compound used in agriculture to kill plant-parasitic nematodes. The crystal structure of the heterohexameric trans-3-chloroacrylic acid dehalogenase (CaaD) from Pseudomonas pavonaceae 170 inactivated by 3-bromopropiolate shows that Glu-52 in the alpha-subunit is positioned to function as the water-activating base for the addition of a hydroxyl group to C-3 of 3-chloroacrylate and 3-bromopropiolate, whereas the nearby Pro-1 in the beta-subunit is positioned to provide a proton to C-2. Two arginine residues, alphaArg-8 and alphaArg-11, interact with the C-1 carboxylate groups, thereby polarizing the alpha,beta-unsaturated acids. The reaction with 3-chloroacrylate results in the production of an unstable halohydrin, 3-chloro-3-hydroxypropanoate, which decomposes into the products malonate semialdehyde and HCl. In the inactivation mechanism, however, malonyl bromide is produced, which irreversibly alkylates the betaPro-1. CaaD is related to 4-oxalocrotonate tautomerase, with which it shares an N-terminal proline. However, in 4-oxalocrotonate tautomerase, Pro-1 functions as a base participating in proton transfer within a hydrophobic active site, whereas in CaaD, the acidic proline is stabilized in a hydrophilic active site. The altered active site environment of CaaD thus facilitates a previously unknown reaction in the tautomerase superfamily, the hydration of the alpha,beta-unsaturated bonds of trans-3-chloroacrylate and 3-bromopropiolate. The mechanism for these hydration reactions represents a novel catalytic strategy that results in carbon-halogen bond cleavage.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Binding Sites
  • Catalysis
  • Hydrolases / chemistry*
  • Models, Molecular
  • Protein Conformation
  • Pseudomonas / enzymology
  • Water / chemistry*
  • X-Ray Diffraction

Substances

  • Water
  • Hydrolases
  • trans-3-chloroacrylic acid dehalogenase

Associated data

  • PDB/1S0Y