1KJX: Imp Complex Of E. Coli Adenylosuccinate Synthetase

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.
PDB ID: 1KJXDownload
MMDB ID: 71109
PDB Deposition Date: 2001/12/5
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 2.6  Å
Source Organism:
Similar Structures:
Biological Unit for 1KJX: dimeric; determined by author and by software (PISA,PQS)
Molecular Components in 1KJX
Label Count Molecule
Proteins (2 molecules)
Adenylosuccinate Synthetase(Gene symbol: purA)
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

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