title: Structural and kinetic characterization of quinolinate phosphoribosyltransferase (hQPRTase) from homo sapiens.
abstract: Human quinolinate phosphoribosyltransferase (EC 2.4.2.19) (hQPRTase) is a member of the type II phosphoribosyltransferase family involved in the catabolism of quinolinic acid (QA). It catalyses the formation of nicotinic acid mononucleotide from quinolinic acid, which involves a phosphoribosyl transfer reaction followed by decarboxylation. hQPRTase has been implicated in a number of neurological conditions and in order to study it further, we have carried out structural and kinetic studies on recombinant hQPRTase. The structure of the fully active enzyme overexpressed in Escherichia coli was solved using multiwavelength methods to a resolution of 2.0 A. hQPRTase has a alpha/beta barrel fold sharing a similar overall structure with the bacterial QPRTases. The active site of hQPRTase is located at an alpha/beta open sandwich structure that serves as a cup for the alpha/beta barrel of the adjacent subunit with a QA binding site consisting of three arginine residues (R102, R138 and R161) and two lysine residues (K139 and K171). Mutation of these residues affected substrate binding or abolished the enzymatic activity. The kinetics of the human enzyme are different to the bacterial enzymes studied, hQPRTase is inhibited competitively and non-competitively by one of its substrates, 5-phosphoribosylpyrophosphate (PRPP). The human enzyme adopts a hexameric arrangement, which places the active sites in close proximity to each other.
authors.affiliation: The Centre for Biomolecular Science, The University of St Andrews, North Haugh, St. Andrews KY16 9ST, Scotland.
authors.forename: Huanting
authors.initials: H
authors.lastname: Liu
authors.forename: Kerry
authors.initials: K
authors.lastname: Woznica
authors.forename: Gemma
authors.initials: G
authors.lastname: Catton
authors.forename: Amanda
authors.initials: A
authors.lastname: Crawford
authors.forename: Nigel
authors.initials: N
authors.lastname: Botting
authors.forename: James H
authors.initials: JH
authors.lastname: Naismith
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010430:Pentosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010754:Phosphoribosyl Pyrophosphate / Q000378:metabolism*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D000098553:Nicotinate-Nucleotide Diphosphorylase (Carboxylating)
chemical_list: D010754:Phosphoribosyl Pyrophosphate; D010430:Pentosyltransferases; D000098553:Nicotinate-Nucleotide Diphosphorylase (Carboxylating)