CHARACTERIZATION AND FUNCTIONAL EXPRESSION OF THE CDNA-ENCODING HUMANBRAIN QUINOLINATE PHOSPHORIBOSYLTRANSFERASE

Mammalian quinolinate phosphoribusyltransferase (QPRTase) (EC 2.4.2.19 ) is a key enzyme in catabolism of quinolinate, an intermediate in the tryptophan-nicotinamide adenine dinucleotide (NAD) pathway. Quinolina te acts as a most potent endogenous exitotoxin to neurons. Elevation o f quinolinate levels in the brain has been linked to the pathogenesis of neurodegenerative disorders. iis the first step to elucidate molecu lar basis underlying the quinolinate metabolism, the cDNA encoding hum an brain QPRTase was cloned and characterized. Utilizing partial amino acid sequences obtained from highly purified porcine kidney QPRTase, a human isolog was obtained from a human brain cDNA library. The cDNA encodes a open reading frame of 247 amino acids, and shares 30 to 40% identity with those of bacterial QPRTases. To confirm that the cDNA cl one encodes human QPRTase, its functional expression was studied in a bacterial host. Introduction of the human cDNA into a QPRTase defectiv e (nadC) E. coli strain brought about an abrupt increase in QPRTase ac tivity and allowed the cells to grow in the absence of nicotinic acid. It is concluded that the cloned cDNA encodes human QPRTase which is f unctional beyond the phylogenic boundary. (C) 1998 Elsevier Science B. V.