1l1r: Difference between revisions

[[Image:1l1r.jpg|left|200px]]<br /><applet load="1l1r" size="350" color="white" frame="true" align="right" spinBox="true"  

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.

1L1R is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Giardia_intestinalis Giardia intestinalis] with <scene name='pdbligand=MG:'>MG</scene>, <scene name='pdbligand=9DA:'>9DA</scene> and <scene name='pdbligand=PRP:'>PRP</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Adenine_phosphoribosyltransferase Adenine phosphoribosyltransferase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.4.2.7 2.4.2.7] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1L1R OCA].  

[[Category: Almo, S C.]]

[[Category: Sarver, A E.]]

[[Category: Schramm, V L.]]

[[Category: Tanaka, K S.]]

[[Category: Wang, C C.]]

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