1kkb
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Complex of Escherichia coli Adenylosuccinate Synthetase with IMP and Hadacidin
OverviewOverview
A complete set of substrate/substrate analogs of adenylosuccinate synthetase from Escherichia coli induces dimer formation and a transition from a disordered to an ordered active site. The most striking of the ligand-induced effects is the movement of loop 40-53 by up to 9 A. Crystal structures of the partially ligated synthetase, which either combine IMP and hadacidin or IMP, hadacidin, and Mg(2+)-pyrophosphate, have ordered active sites, comparable with the fully ligated enzyme. More significantly, a crystal structure of the synthetase with IMP alone exhibits a largely ordered active site, which includes the 9 A movement of loop 40-53 but does not include conformational adjustments to backbone carbonyl 40 (Mg(2+) interaction element) and loop 298-304 (L-aspartate binding element). Interactions involving the 5'-phosphoryl group of IMP evidently trigger the formation of salt links some 30 A away. The above provides a structural basis for ligand binding synergism, effects on k(cat) due to mutations far from the site of catalysis, and the complete loss of substrate efficacy due to minor alterations of the 5'-phosphoryl group of IMP.
About this StructureAbout this Structure
1KKB is a Single protein structure of sequence from Escherichia coli with and as ligands. Active as Adenylosuccinate synthase, with EC number 6.3.4.4 Full crystallographic information is available from OCA.
ReferenceReference
IMP Alone Organizes the Active Site of Adenylosuccinate Synthetase from Escherichia coli., Hou Z, Wang W, Fromm HJ, Honzatko RB, J Biol Chem. 2002 Feb 22;277(8):5970-6. Epub 2001 Dec 12. PMID:11741996
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