Structural and Kinetic Characterization of Quinolinate Phosphoribosyltransferase (hQPRTase) from Homo sapiens

• Published in: Journal of molecular biology Vol. 373; no. 3; pp. 755 - 763
• Main Authors: Liu, Huanting, Woznica, Kerry, Catton, Gemma, Crawford, Amanda, Botting, Nigel, Naismith, James H.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 26.10.2007
• Subjects: 5-phosphoribosylpyrophosphate; Amino Acid Sequence; Binding Sites; Catalysis; Crystallography, X-Ray; Escherichia coli; Homo sapiens quinolinate phosphoribosyltransferase; Humans; Kinetics; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; NAD biosynthesis; nicotinic acid mononucleotide; Pentosyltransferases - chemistry; Pentosyltransferases - genetics; Pentosyltransferases - metabolism; Phosphoribosyl Pyrophosphate - metabolism; Protein Conformation; quinolinic acid; Sequence Homology, Amino Acid; Substrate Specificity; Tt; St; 5-phosphoribosylpyrophosphate; Se-Met; PRPP; Mt; Hp; quinolinic acid; hQPRTase; QA; NAMN; MAD; nicotinic acid mononucleotide; NAD biosynthesis; Tm; Homo sapiens quinolinate phosphoribosyltransferase
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2007.08.043

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 Å. hQPRTase has a α/β barrel fold sharing a similar overall structure with the bacterial QPRTases. The active site of hQPRTase is located at an α/β open sandwich structure that serves as a cup for the α/β 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.