Phosphorylated and dephosphorylated structures of pig heart, GTP-specific succinyl-CoA synthetase

Succinyl-CoA synthetase (SCS) catalyzes the reversible phosphorylation/ dep hosphorylation reaction: succinyl-CoA + NDP + P-i <----> succinate + CoA + NTP where N denotes adenosine or guanosine. In the course of the reaction, an e ssential histidine residue is transiently phosphorylated. We have crystalli zed and solved the structure of the GTP-specific isoform of SCS from pig he art (EC 6.2.1.4) in both the dephosphorylated and phosphorylated forms. The structures were refined to 2.1 Angstrom resolution. In the dephosphorylate d structure, the enzyme is stabilized via coordination of a phosphate ion b y the active-site histidine residue and the two "power" helices, one contri buted by each subunit of the alpha beta-dimer. Small changes in the conform ations of residues at the amino terminus of the power helix contributed by the alpha-subunit allow the enzyme to accommodate either the covalently bou nd phosphoryl group or the free phosphate ion. Structural comparisons are m ade between the active sites in these two forms of the enzyme, both of whic h can occur along the catalytic path. Comparisons are also made with the st ructure of Escherichia coli SCS. The domain that has been shown to bind ADP in E, coil SCS is more open in the pig heart, GTP-specific SCS structure. (C) 2000 Academic Press.