title: Molecular cloning and characterization of a tumor-associated, growth-related, and time-keeping hydroquinone (NADH) oxidase (tNOX) of the HeLa cell surface.
abstract: NOX proteins are growth-related cell surface proteins that catalyze both hydroquinone or NADH oxidation and protein disulfide interchange and exhibit prion-like properties. The two enzymatic activities alternate to generate a regular period length of about 24 min. Here we report the expression, cloning, and characterization of a tumor-associated NADH oxidase (tNOX). The cDNA sequence of 1830 bp is located on gene Xq25-26 with an open reading frame encoding 610 amino acids. The activities of the bacterially expressed tNOX oscillate with a period length of 22 min as is characteristic of tNOX activities in situ. The activities are inhibited completely by capsaicin, which represents a defining characteristic of tNOX activity. Functional motifs identified by site-directed mutagenesis within the C-terminal portion of the tNOX protein corresponding to the processed plasma membrane-associated form include quinone (capsaicin), copper and adenine nucleotide binding domains, and two cysteines essential for catalytic activity. Four of the six cysteine to alanine replacements retained enzymatic activity, but the period lengths of the oscillations were increased. A single protein with two alternating enzymatic activities indicative of a time-keeping function is unprecedented in the biochemical literature.
authors.affiliation: Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Pin-Ju
authors.initials: PJ
authors.lastname: Chueh
authors.forename: Chinpal
authors.initials: C
authors.lastname: Kim
authors.forename: NaMi
authors.initials: N
authors.lastname: Cho
authors.forename: Dorothy M
authors.initials: DM
authors.lastname: Morré
authors.forename: D James
authors.initials: DJ
authors.lastname: Morré
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002211:Capsaicin / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D013453:Sulfonylurea Compounds / Q000494:pharmacology
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D009363:Neoplasm Proteins; D013453:Sulfonylurea Compounds; C062821:LY 181984; D009247:NADH, NADPH Oxidoreductases; C431909:tumor-associated NADH oxidase; D002211:Capsaicin