Structures of ternary complexes of BphK, a bacterial glutathione S-transferase that reductively dechlorinates polychlorinated biphenyl metabolites.
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Tocheva EI, Fortin PD, Eltis LD, Murphy ME
Structures of ternary complexes of BphK, a bacterial glutathione S-transferase that reductively dechlorinates polychlorinated biphenyl metabolites.
J Biol Chem. 2006 Oct 13;281(41):30933-40. Epub 2006 Aug 17.
- PubMed ID
- 16920719 [ View in PubMed]
- Abstract
Prokaryotic glutathione S-transferases are as diverse as their eukaryotic counterparts but are much less well characterized. BphK from Burkholderia xenovorans LB400 consumes two GSH molecules to reductively dehalogenate chlorinated 2-hydroxy-6-oxo-6-phenyl-2,4-dienoates (HOPDAs), inhibitory polychlorinated biphenyl metabolites. Crystallographic structures of two ternary complexes of BphK were solved to a resolution of 2.1A. In the BphK-GSH-HOPDA complex, GSH and HOPDA molecules occupy the G- and H-subsites, respectively. The thiol nucleophile of the GSH molecule is positioned for SN2 attack at carbon 3 of the bound HOPDA. The respective sulfur atoms of conserved Cys-10 and the bound GSH are within 3.0A, consistent with product release and the formation of a mixed disulfide intermediate. In the BphK-(GSH)2 complex, a GSH molecule occupies each of the two subsites. The three sulfur atoms of the two GSH molecules and Cys-10 are aligned suitably for a disulfide exchange reaction that would regenerate the resting enzyme and yield disulfide-linked GSH molecules. A second conserved residue, His-106, is adjacent to the thiols of Cys-10 and the GSH bound to the G-subsite and thus may stabilize a transition state in the disulfide exchange reaction. Overall, the structures support and elaborate a proposed dehalogenation mechanism for BphK and provide insight into the plasticity of the H-subsite.