Interactions of GTP with the ATP-grasp domain of GTP-specific succinyl-CoA synthetase.
Two isoforms of succinyl-CoA synthetase exist in mammals, one specific for ATP and the other for GTP. The GTP-specific form of pig succinyl-CoA synthetase has been crystallized in the presence of GTP and the structure determined to 2.1 A resolution. GTP is bound in the ATP-grasp domain, where interactions of the guanine base with a glutamine residue (Gln-20beta) and with backbone atoms provide the specificity. The gamma-phosphate interacts with the side chain of an arginine residue (Arg-54beta) and with backbone amide nitrogen atoms, leading to tight interactions between the gamma-phosphate and the protein. This contrasts with the structures of ATP bound to other members of the family of ATP-grasp proteins where the gamma-phosphate is exposed, free to react with the other substrate. To test if GDP would interact with GTP-specific succinyl-CoA synthetase in the same way that ADP interacts with other members of the family of ATP-grasp proteins, the structure of GDP bound to GTP-specific succinyl-CoA synthetase was also determined. A comparison of the conformations of GTP and GDP shows that the bases adopt the same position but that changes in conformation of the ribose moieties and the alpha- and beta-phosphates allow the gamma-phosphate to interact with the arginine residue and amide nitrogen atoms in GTP, while the beta-phosphate interacts with these residues in GDP. The complex of GTP with succinyl-CoA synthetase shows that the enzyme is able to protect GTP from hydrolysis when the active-site histidine residue is not in position to be phosphorylated.
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada. frasm@ucalgary.ca
Marie E
ME
Fraser
Koto
K
Hayakawa
Millicent S
MS
Hume
David G
DG
Ryan
Edward R
ER
Brownie
D000255:Adenosine Triphosphate / Q000737:chemistry*; D000818:Animals; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005973:Glutamine / Q000737:chemistry; D006147:Guanine / Q000737:chemistry; D006160:Guanosine Triphosphate / Q000737:chemistry* / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry; D006868:Hydrolysis; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms; D012266:Ribose / Q000737:chemistry; D013389:Succinate-CoA Ligases / Q000737:chemistry* / Q000378:metabolism; D013552:Swine
D010710:Phosphates; D020033:Protein Isoforms; D005973:Glutamine; D006639:Histidine; D006147:Guanine; D012266:Ribose; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D001120:Arginine; D013389:Succinate-CoA Ligases; D009584:Nitrogen