Tight Coupling of Partial Reactions in the Acetyl-CoA Decarbonylase/Synthase (ACDS) Multienzyme Complex from Methanosarcina thermophila

Cation distribution and mixing thermodynamics in Fe/Ni thiospinels

“…At low concentrations (x < 0.2) there is a strong preference for octahedral (B) site occupation of Ni. This is an interesting result because it somehow breaks the analogy between Ni-doped greigite and biological enzymes with (Fe, Ni)S clusters, where Ni is usually tetra-coordinated (Volbeda et al, 1995;Dobbek et al, 2001;FontecillaCamps, 2003, 2005;Svetlitchnyi et al, 2004;Ragsdale, 2009;Gencic et al, 2010). The analogy in coordination environment is better for the thiospinels with higher Ni concentrations (x > 0.25), for which Ni ions locate preferentially in the tetrahedral (A) sites.…”

“…For instance, when the enzyme is in the oxidised state, Ni is in square-planar coordination, while Fe is square-pyramidal; in the reduced state, Ni exhibits a square-pyramidal coordination, and the Fe has an octahedral geometry (Volbeda et al, 1995;Volbeda and Fontecilla-Camps, 2005;Canaguier et al, 2008). In the case of CODH (carbon monoxide dehydrogenase -responsible for the catalysis of CO 2 to CO (Russell and Martin, 2004;Ragsdale, 2009)), Ni is in a tetrahedrally distorted squareplanar coordination, with the proximal Fe also displaying tetrahedral geometry (Dobbek et al, 2001;Svetlitchnyi et al, 2004;Gencic et al, 2010). This is also the case for the distal Ni in acetyl coenzyme-A synthetase (ACS) (the enzyme which acts to combine the resultant CO with a methyl group (Volbeda and Fontecilla-Camps, 2005)), where Ni exhibits a square-planar geometry (Lindahl, 2004).…”

The extended reductive acetyl-CoA pathway: ATPases in metal cluster maturation and reductive activation

“…CODHs acting in the reductive acetylCoA pathway are typically associated with ACS in a stable complex, in which the generated CO binds to the Ni-Ni-[4Fe-4S] site of ACS (Ragsdale et al, 1985;Doukov et al, 2002;Darnault et al, 2003;Svetlitchnyi et al, 2004). Some archaea contain CODHs in a large complex, where it is associated with ACS and a corrinoid-iron/sulfur protein (Grahame, 1991;Gencic et al, 2010).…”

Acetate Metabolism in Anaerobes from the Domain Archaea

“…A mechanism is proposed in which transfer of an electron from “C” to “A” maintains the reduced catalytically active Ni(I) redox state of “A” [ 74 ]. Both kinetic and EPR approaches support the fact that alterations in the Ni coordination environment of the “A” cluster promote C−C bond cleavage, dependent on changes in the protein conformation from the open to closed state [ 75 , 76 ]. Moreover, CO is proposed to be an inhibitor of C-C bond cleavage; thus, control over C−C bond cleavage in concert with containment of CO in the gas channel explains the requirement for tight coupling of the decarbonylation reaction for efficient transfer of CO to “C” for oxidation [ 75 ].…”

“…Both kinetic and EPR approaches support the fact that alterations in the Ni coordination environment of the “A” cluster promote C−C bond cleavage, dependent on changes in the protein conformation from the open to closed state [ 75 , 76 ]. Moreover, CO is proposed to be an inhibitor of C-C bond cleavage; thus, control over C−C bond cleavage in concert with containment of CO in the gas channel explains the requirement for tight coupling of the decarbonylation reaction for efficient transfer of CO to “C” for oxidation [ 75 ]. The γδ component transfers the methyl group of acetyl-CoA to THSPt, involving a corrinoid cofactor and an iron-sulfur cluster [ 55 , 77 , 78 , 79 ], although it has yet to be determined which of the two subunits interact with THSPt.…”