1ibs
From Proteopedia
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PHOSPHORIBOSYLDIPHOSPHATE SYNTHETASE IN COMPLEX WITH CADMIUM IONS
Overview
The binding sites for the two cations essential for the catalytic function, of 5-phospho-D-ribosyl alpha-1-diphosphate (PRPP) synthases have been, identified from the structure of the Bacillus subtilis, phosphoribosyldiphosphate synthetase (PRPPsase) with bound Cd(2+). The, structure determined from X-ray diffraction data to 2.8-A resolution, reveals the same hexameric arrangement of the subunits that was observed, in the complexes of the enzyme with the activator sulfate and the, allosteric inhibitor ADP. Two cation binding sites were localized in each, of the two domains of the subunits that compose the hexamer; each domain, of the subunit has an associated cation. In addition to the bound Cd(2+), the Cd(2+)-PRPPsase structure contains a sulfate ion in the regulatory, site, a sulfate ion at the ribose-5-phosphate binding site, and an AMP, moiety at the ATP binding site. Comparison of the Cd(2+)-PRPPsase to the, structures of the PRPPsase complexed with sulfate and mADP reveals the, structural rearrangement induced by the binding of the free cation, which, is essential for the initiation of the reaction. The comparison to the, cPRPP complex of glutamine phosphoribosylpyrophosphate amidotransferase, from Escherichia coli, a type I phosphoribosyltransferase, provided, information about the binding of PRPP. This strongly indicates that the, binding of both substrates must lead to a stabilized conformation of the, loop region, which remains unresolved in the known PRPPsase complex, structures.
About this Structure
1IBS is a Single protein structure of sequence from Bacillus subtilis with SO4, CD and ABM as ligands. Active as Ribose-phosphate diphosphokinase, with EC number 2.7.6.1 Full crystallographic information is available from OCA.
Reference
Binding of cations in Bacillus subtilis phosphoribosyldiphosphate synthetase and their role in catalysis., Eriksen TA, Kadziola A, Larsen S, Protein Sci. 2002 Feb;11(2):271-9. PMID:11790837
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