1qap
|
QUINOLINIC ACID PHOSPHORIBOSYLTRANSFERASE WITH BOUND QUINOLINIC ACID
OverviewOverview
BACKGROUND: Quinolinic acid (QA) is a neurotoxin and has been shown to be, present at high levels in the central nervous system of patients with, certain diseases, such as AIDS and meningitis. The enzyme quinolinic acid, phosphoribosyltransferase (QAPRTase) provides the only route for QA, metabolism and is also an essential step in de novo NAD biosynthesis., QAPRTase catalyzes the synthesis of nicotinic acid mononucleotide (NAMN), from QA and 5-phosphoribosyl-1-pyrophosphate (PRPP). The structures of, several phosphoribosyltransferases (PRTases) have been reported, and all, have shown a similar fold of a five-strandard beta sheet surrounded by, four alpha helices. A conserved sequence motif of 13 residues is common to, these 'type I' PRTases but is not observed in the QAPRTase sequence, suggestive of a different fold for this enzyme. RESULTS: The crystal, structure of QAPRTase from Salmonella typhimurium has been determined with, bound QA to 2.8 A resolution, and with bound NAMN to 3.0 A resolution., Most significantly, the enzyme shows a completely novel fold for a PRTase, enzyme comprising a two-domain structure: a mixed alpha/beta N-terminal, domain and an alpha/beta barrel-like domain containing seven beta strands., The active site is located at the C-terminal ends of the beta strands of, the alpha/beta barrel, and is bordered by the N-terminal domain of the, second subunit of the dimer. The active site is largely composed of a, number of conserved charged residues that appear to be important for, substrate binding and catalysis. CONCLUSIONS: The seven-stranded, alpha/beta-barrel domain of QAPRTase is very similar in structure to the, eight-stranded alpha/beta-barrel enzymes. The structure shows a, phosphate-binding site that appears to be conserved among many, alpha/beta-barrel enzymes including indole-3-glycerol phosphate synthase, and flavocytochrome b2. The new fold observed here demonstrates that the, PRTase enzymes have evolved their similar chemistry from at least two, completely different protein architectures.
About this StructureAbout this Structure
1QAP is a Single protein structure of sequence from Salmonella typhimurium with NTM as ligand. Active as Nicotinate-nucleotide diphosphorylase (carboxylating), with EC number 2.4.2.19 Full crystallographic information is available from OCA.
ReferenceReference
A new function for a common fold: the crystal structure of quinolinic acid phosphoribosyltransferase., Eads JC, Ozturk D, Wexler TB, Grubmeyer C, Sacchettini JC, Structure. 1997 Jan 15;5(1):47-58. PMID:9016724
Page seeded by OCA on Wed Nov 21 00:32:18 2007