Electronic and geometric structures of the organophosphate-degrading enzyme from Agrobacterium radiobacter (OpdA)

J Biol Inorg Chem. 2011 Jun;16(5):777-87. doi: 10.1007/s00775-011-0779-6. Epub 2011 Apr 13.

Abstract

The organophosphate-degrading enzyme from Agrobacterium radiobacter (OpdA) is a highly efficient catalyst for the degradation of pesticides and some nerve agents such as sarin. OpdA requires two metal ions for catalytic activity, and hydrolysis is initiated by a nucleophilic hydroxide that is bound to one of these metal ions. The precise location of this nucleophile has been contentious, with both a terminal and a metal-ion-bridging hydroxide as likely candidates. Here, we employed magnetic circular dichroism to probe the electronic and geometric structures of the Co(II)-reconstituted dinuclear metal center in OpdA. In the resting state the metal ion in the more secluded α site is five-coordinate, whereas the Co(II) in the solvent-exposed β site is predominantly six-coordinate with two terminal water ligands. Addition of the slow substrate diethyl 4-methoxyphenyl phosphate does not affect the α site greatly but lowers the coordination number of the β site to five. A reduction in the exchange coupling constant indicates that substrate binding also triggers a shift of the μ-hydroxide into a pseudoterminal position in the coordination sphere of either the α or the β metal ion. Mechanistic implications of these observations are discussed.

Publication types

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

MeSH terms

  • Agrobacterium tumefaciens / chemistry
  • Agrobacterium tumefaciens / enzymology*
  • Bacterial Proteins / chemistry*
  • Circular Dichroism
  • Cobalt / chemistry*
  • Crystallography, X-Ray
  • Electrons
  • Models, Molecular
  • Organophosphates / metabolism*
  • Protein Conformation

Substances

  • Bacterial Proteins
  • Organophosphates
  • Cobalt