title: Modeling carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS): a trinuclear nickel complex employing deprotonated amides and bridging thiolates.
abstract: Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) utilizes a unique Ni-M bimetallic site in the biosynthesis of acetyl-CoA, where a square-planar Ni ion is coordinated to two thiolates and two deprotonated amides in a Cys-Gly-Cys motif. The identity of M is currently a matter of debate, although both Cu and Ni have been proposed. In an effort to model ACS's unusual active site and to provide insight into the mechanism of acetyl-CoA formation and the role of each of the metals ions, we have prepared and structurally characterized a number of Ni(II)-peptide mimic complexes. The mononuclear complexes Ni(II) N, N'-bis(2-mercaptoethyl)oxamide (1), Ni(II) N, N'-ethylenebis(2-mercaptoacetamide) (2), and Ni(II) N, N'-ethylenebis(2-mercaptopropionamide) (3) model the Ni(Cys-Gly-Cys) site and can be used as synthons for additional multinuclear complexes. Reaction of 2 with MeI resulted in the alkylation of the sulfur atoms and the formation of Ni(II) N, N'-ethylenebis(2-methylmercaptoacetamide) (4), demonstrating the nucleophilicity of the terminal alkyl thiolates. Addition of Ni(OAc)(2).4H(2)O to3 resulted in the formation of a trinuclear species (5), while 2 crystallizes as an unusual paddlewheel complex (6) in the presence of nickel acetate. The difference in reactivity between the similar complexes 2 and 3 highlights the importance of ligand design when synthesizing models of ACS. Significantly,5 maintains the key features observed in the active site of ACS, namely a square-planar Ni coordinated to two deprotonated amides and two thiolates, where the thiolates bridge to a second metal, suggesting that 5 is a reasonable structural model for this unique enzyme.
authors.affiliation: Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112-0850, USA.
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Hatlevik
authors.forename: Mary C
authors.initials: MC
authors.lastname: Blanksma
authors.forename: Vaidyanathan
authors.initials: V
authors.lastname: Mathrubootham
authors.forename: Atta M
authors.initials: AM
authors.lastname: Arif
authors.forename: Eric L
authors.initials: EL
authors.lastname: Hegg
mesh_terms: D000106:Acetate-CoA Ligase / Q000737:chemistry*; D000445:Aldehyde Oxidoreductases / Q000737:chemistry*; D000577:Amides / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray; D007202:Indicators and Reagents; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D011487:Protein Conformation; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013439:Sulfhydryl Reagents / Q000737:chemistry
chemical_list: D000577:Amides; D007202:Indicators and Reagents; D009097:Multienzyme Complexes; D013439:Sulfhydryl Reagents; D009532:Nickel; D000445:Aldehyde Oxidoreductases; C019823:carbon monoxide dehydrogenase; D000106:Acetate-CoA Ligase; D010100:Oxygen