Crystallographic snapshots of cyanide- and water-bound C-clusters from bifunctional carbon monoxide dehydrogenase/acetyl-CoA synthase.
Nickel-containing carbon monoxide dehydrogenases (CODHs) reversibly catalyze the oxidation of carbon monoxide to carbon dioxide and are of vital importance in the global carbon cycle. The unusual catalytic CODH C-cluster has been crystallographically characterized as either a NiFe(4)S(4) or a NiFe(4)S(5) metal center, the latter containing a fifth, additional sulfide that bridges Ni and a unique Fe site. To determine whether this bridging sulfide is catalytically relevant and to further explore the mechanism of the C-cluster, we obtained crystal structures of the 310 kDa bifunctional CODH/acetyl-CoA synthase complex from Moorella thermoacetica bound both with a substrate H(2)O/OH(-) molecule and with a cyanide inhibitor. X-ray diffraction data were collected from native crystals and from identical crystals soaked in a solution containing potassium cyanide. In both structures, the substrate H(2)O/OH(-) molecule exhibits binding to the unique Fe site of the C-cluster. We also observe cyanide binding in a bent conformation to Ni of the C-cluster, adjacent the substrate H(2)O/OH(-) molecule. Importantly, the bridging sulfide is not present in either structure. As these forms of the C-cluster represent the coordination environment immediately before the reaction takes place, our findings do not support a fifth, bridging sulfide playing a catalytic role in the enzyme mechanism. The crystal structures presented here, along with recent structures of CODHs from other organisms, have led us toward a unified mechanism for CO oxidation by the C-cluster, the catalytic center of an environmentally important enzyme.
Kung
Yan
Y
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Doukov
Tzanko I
TI
Seravalli
Javier
J
Ragsdale
Stephen W
SW
Drennan
Catherine L
CL
D000106:Acetate-CoA Ligase / Q000737:chemistry* / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000737:chemistry*; D008024:Ligands; D017021:Methanosarcina barkeri; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000737:chemistry*
D003486:Cyanides; D008024:Ligands; D009097:Multienzyme Complexes; D014867:Water; D000445:Aldehyde Oxidoreductases; C019823:carbon monoxide dehydrogenase; D000106:Acetate-CoA Ligase