Abstract
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 Å 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.
Original language | English (US) |
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Pages (from-to) | 881-887 |
Number of pages | 7 |
Journal | Nature Structural Biology |
Volume | 3 |
Issue number | 10 |
DOIs | |
State | Published - Oct 1996 |
ASJC Scopus subject areas
- Structural Biology
- Biochemistry
- Genetics