Quinone Electrophiles Selectively Adduct "Electrophile Binding Motifs" within Cytochrome c
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- 作者：Ashley A. Fisher ; Matthew T. Labenski ; Srinivas Malladi ; Vijay Gokhale ; Martina E. Bowen ; Rania S. Milleron ; Shawn B. Bratton ; Terrence J. Monks ; Serrine S. Lau
- 刊名：Biochemistry
- 出版年：2007
- 出版时间：October 2, 2007
- 年：2007
- 卷：46
- 期：39
- 页码：11090 - 11100
- 全文大小：484K
- 年卷期：v.46,no.39(October 2, 2007)
- ISSN：1520-4995
文摘
Electrophiles generated endogenously, or via the metabolic bioactivation of drugs and otherenvironmental chemicals, are capable of binding to a variety of nucleophilic sites within proteins. Factorsthat determine site selective susceptibility to electrophile-mediated post-translational modifications, andthe consequences of such alterations, remain largely unknown. To identify and characterize chemical-mediated protein adducts, electrophiles with known toxicity were utilized. Hydroquinone, and its mercapturicacid pathway metabolites, cause renal proximal tubular cell necrosis and nephrocarcinogenicity in rats.The adverse effects of HQ and its thioether metabolites are in part a consequence of their oxidation to thecorresponding electrophilic 1,4-benzoquinones (BQ). We now report that BQ and 2-(N-acetylcystein-S-yl)benzoquinone (NAC-BQ) preferentially bind to solvent-exposed lysine-rich regions within cytochromec. Furthermore, we have identified specific glutamic acid residues within cytochrome c as novel sites ofNAC-BQ adduction. The microenvironment at the site of adduction governs both the initial specificityand the structure of the final adduct. The solvent accessibility and local pKa of the adducted and neighboringamino acids contribute to the selectivity of adduction. Postadduction chemistry subsequently alters thenature of the final adduct. Using molecular modeling, the impact of BQ and NAC-BQ adduction oncytochrome c was visualized, revealing the spatial rearrangement of critical residues necessary for protein-protein interactions. Consequently, BQ-adducted cytochrome c fails to initiate caspase-3 activation innative lysates and also inhibits Apaf-1 oligomerization into an apoptosome complex in a purely reconstitutedsystem. In summary, a combination of mass spectroscopic, molecular modeling, and biochemical approachesconfirms that electrophile-protein adducts produce structural alterations that influence biological function.