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Crystal Structure of APRTase from Giardia lamblia Complexed with 9-deazaadenine, Mg2+ and PRPP
Structural highlights
FunctionEvolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe 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. 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[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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