Electric-Field-Induced Redox Potential Shifts of Tetraheme Cytochromes c

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• 作者：Laura Rivas ; Clá ; udio M. Soares ; Antó ; nio M. Baptista ; Jalila Simaan ; Roberto E. Di Paolo ; Daniel H. Murgida ; Peter Hildebr ; t
• 刊名：Biophysical Journal
• 出版年：2005
• 出版时间：June 2005
• 年：2005
• 卷：88
• 期：6
• 页码：4188-4199
• 全文大小：330 K

文摘

The tetraheme protein cytochrome c₃ (Cyt-c₃) from Desulfovibrio gigas, immobilized on a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid, is studied by theoretical and spectroscopic methods. Molecular dynamics simulations indicate that the protein docks to the negatively charged SAM via its lysine-rich domain around the exposed heme IV. Complex formation is associated with only little protein structural perturbations. This finding is in line with the resonance Raman and surface-enhanced resonance Raman (SERR) spectroscopic results that indicate essentially the same heme pocket structures for the protein in solution and adsorbed on SAM-coated Ag electrodes. Electron- and proton-binding equilibrium calculations reveal substantial negative shifts of the redox potentials compared to the protein in solution. The magnitude of these shifts decreases in the order heme IV (−161 mV) > heme III (−73 mV) > heme II (−57 mV) > heme I (−26 mV), resulting in a change of the order of reduction. These shifts originate from the distance-dependent electrostatic interactions between the SAM headgroups and the individual hemes, leading to a stabilization of the oxidized forms. The results of the potential-dependent SERR spectroscopic analyses are consistent with the theoretical predictions and afford redox potential shifts of −160 mV (heme IV), −90 mV (heme III), −70 mV (heme II), and +20 mV (heme I) relative to the experimental redox potentials for Cyt-c₃ in solution. SERR spectroscopic experiments reveal electric-field-induced changes of the redox potentials also for the structurally very similar Cyt-c₃ from Desulfovibrio vulgaris, although the shifts are somewhat smaller compared to Cyt-c₃ from D. gigas. This study suggests that electric-field-induced redox potential shifts may also occur upon binding to biomembranes or partner proteins and thus may affect biological electron transfer processes.