title: Regulation of the activity of Escherichia coli quinolinate synthase by reversible disulfide-bond formation.
abstract: Quinolinate synthase (NadA) catalyzes a unique condensation reaction between dihydroxyacetone phosphate and iminoaspartate, yielding inorganic phosphate, 2 mol of water, and quinolinic acid, a central intermediate in the biosynthesis of nicotinamide adenine dinucleotide and its derivatives. The enzyme from Escherichia coli contains a C (291)XXC (294)XXC (297) motif in its primary structure. Bioinformatics analysis indicates that only Cys297 serves as a ligand to a [4Fe-4S] cluster that is required for turnover. In this report, we show that the two remaining cysteines, Cys291 and Cys294, undergo reversible disulfide-bond formation, which regulates the activity of the enzyme. This mode of redox regulation of NadA appears physiologically relevant, since disulfide-bond formation and reduction are effected by oxidized and reduced forms of E. coli thioredoxin. A midpoint potential of -264 +/- 1.77 mV is approximated for the redox couple.
authors.affiliation: Department of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Allison H
authors.initials: AH
authors.lastname: Saunders
authors.forename: Squire J
authors.initials: SJ
authors.lastname: Booker
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017378:Quinolinic Acid / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism
chemical_list: D004220:Disulfides; D009097:Multienzyme Complexes; C022512:quinolinic acid synthetase; D013879:Thioredoxins; D017378:Quinolinic Acid