Publication Abstract from PubMed
Crystal structures of substrate-free and XMP-soaked hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRTase) of the opportunistic pathogen Toxoplasma gondii have been determined to 2.4 and 2.9 A resolution, respectively. HGXPRTase displays the conserved PRTase fold. In the structure of the enzyme bound to its product, a long flexible loop (residues 115-126) is located away from the active site. Comparison to the substrate-free structure reveals a striking relocation of the loop, which is poised to cover the catalytic pocket, thus providing a mechanism by which the HG(X)PRTases shield their oxocarbonium transition states from nucleophilic attack by the bulk solvent. The conserved Ser 117-Tyr 118 dipeptide within the loop is brought to the active site, completing the ensemble of catalytic residues.
Crystal structures of Toxoplasma gondii HGXPRTase reveal the catalytic role of a long flexible loop.,Schumacher MA, Carter D, Ross DS, Ullman B, Brennan RG Nat Struct Biol. 1996 Oct;3(10):881-7. PMID:8836106[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
