Structural Analysis of a Ternary Complex of Allantoate Amidohydrolase from Escherichia Coli Reveals its Mechanics
Purine metabolism plays a major role in regulating the availability of purine nucleotides destined for nucleic acid synthesis. Allantoate amidohydrolase catalyzes the conversion of allantoate to (S)-ureidoglycolate, one of the crucial alternate steps in purine metabolism. The crystal structure of a ternary complex of allantoate amidohydrolase with its substrate allantoate and an allosteric effector, a sulfate ion, from Escherichia coli was determined to understand better the catalytic mechanism and substrate specificity. The 2.25 {angstrom} resolution X-ray structure reveals an {alpha}/{beta} scaffold akin to zinc exopeptidases of the peptidase M20 family and lacks the ({beta}/{alpha}){sub 8}-barrel fold characteristic of the amidohydrolases. Arrangement of the substrate and the two co-catalytic zinc ions at the active site governs catalytic specificity for hydrolysis of N-carbamyl versus the peptide bond in exopeptidases. In its crystalline form, allantoate amidohydrolase adopts a relatively open conformation. However, structural analysis reveals the possibility of a significant movement of domains via rotation about two hinge regions upon allosteric effector and substrate binding resulting in a closed catalytically competent conformation by bringing the substrate allantoate closer to co-catalytic zinc ions. Two cis-prolyl peptide bonds found on either side of the dimerization domain in close proximity to the substrate and ligand-binding sites may be involved in protein folding and in preserving the integrity of the catalytic site.
- Research Organization:
- Brookhaven National Laboratory (BNL) National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 930384
- Report Number(s):
- BNL--81106-2008-JA
- Journal Information:
- Journal of Molecular Biology, Journal Name: Journal of Molecular Biology Journal Issue: 2 Vol. 368; ISSN JMOBAK; ISSN 0022-2836
- Country of Publication:
- United States
- Language:
- English
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