1l1r
Crystal Structure of APRTase from Giardia lamblia Complexed with 9-deazaadenine, Mg2+ and PRPP
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OverviewOverview
The adenine phosphoribosyltransferase (APRTase) from Giardia lamblia was, co-crystallized with 9-deazaadenine and sulfate or with 9-deazaadenine and, Mg-phosphoribosylpyrophosphate. The complexes were solved and refined to, 1.85 and 1.95 A resolution. Giardia APRTase is a symmetric homodimer with, the monomers built around Rossman fold cores, an element common to all, known purine phosphoribosyltransferases. The catalytic sites are capped, with a small hood domain that is unique to the APRTases. These structures, reveal several features relevant to the catalytic function of APRTase: 1), a non-proline cis peptide bond (Glu(61)-Ser(62)) is required to form the, pyrophosphate binding site in the APRTase.9dA.MgPRPP complex but is a, trans peptide bond in the absence of pyrophosphate group, as observed in, the APRTase.9dA.SO4 complex; 2) a catalytic site loop is closed and fully, ordered in both complexes, with Glu(100) from the catalytic loop acting as, the acid/base for protonation/deprotonation of N-7 of the adenine ring; 3), the pyrophosphoryl charge is neutralized by a single Mg2+ ion and Arg(63), in contrast to the hypoxanthine-guanine phosphoribosyltransferases, which, use two Mg2+ ions; and 4) the nearest structural neighbors to APRTases are, the orotate phosphoribosyltransferases, suggesting different paths of, evolution for adenine relative to other purine PRTases. An overlap, comparison of AMP and 9-deazaadenine plus Mg-PRPP at the catalytic sites, of APRTases indicated that reaction coordinate motion involves a 2.1-A, excursion of the ribosyl anomeric carbon, whereas the adenine ring and the, 5-phosphoryl group remained fixed. G. lamblia APRTase therefore provides, another example of nucleophilic displacement by electrophile migration.
About this StructureAbout this Structure
1L1R is a Single protein structure of sequence from Giardia intestinalis with MG, 9DA and PRP as ligands. Active as Adenine phosphoribosyltransferase, with EC number 2.4.2.7 Full crystallographic information is available from OCA.
ReferenceReference
Closed site complexes of adenine phosphoribosyltransferase from Giardia lamblia reveal a mechanism of ribosyl migration., Shi W, Sarver AE, Wang CC, Tanaka KS, Almo SC, Schramm VL, J Biol Chem. 2002 Oct 18;277(42):39981-8. Epub 2002 Aug 8. PMID:12171925
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