Molecular Cloning and Characterization of a Tumor-Associated, Growth-Related, and Time-Keeping Hydroquinone (NADH) Oxidase (tNOX) of the HeLa Cell Surface

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• 作者：Pin-Ju Chueh ; Chinpal Kim ; NaMi Cho ; Dorothy M. Morré ; and D. James Morré
• 刊名：Biochemistry
• 出版年：2002
• 出版时间：March 19, 2002
• 年：2002
• 卷：41
• 期：11
• 页码：3732 - 3741
• 全文大小：219K
• 年卷期：v.41,no.11(March 19, 2002)
• ISSN：1520-4995

文摘

NOX proteins are growth-related cell surface proteins that catalyze both hydroquinone or NADHoxidation and protein disulfide interchange and exhibit prion-like properties. The two enzymatic activitiesalternate to generate a regular period length of about 24 min. Here we report the expression, cloning, andcharacterization of a tumor-associated NADH oxidase (tNOX). The cDNA sequence of 1830 bp is locatedon gene Xq25-26 with an open reading frame encoding 610 amino acids. The activities of the bacteriallyexpressed 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 tNOXactivity. Functional motifs identified by site-directed mutagenesis within the C-terminal portion of thetNOX protein corresponding to the processed plasma membrane-associated form include quinone(capsaicin), copper and adenine nucleotide binding domains, and two cysteines essential for catalyticactivity. Four of the six cysteine to alanine replacements retained enzymatic activity, but the period lengthsof the oscillations were increased. A single protein with two alternating enzymatic activities indicative ofa time-keeping function is unprecedented in the biochemical literature.