title: Electric-field-induced redox potential shifts of tetraheme cytochromes c3 immobilized on self-assembled monolayers: surface-enhanced resonance Raman spectroscopy and simulation studies.
abstract: The tetraheme protein cytochrome c(3) (Cyt-c(3)) 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-c(3) in solution. SERR spectroscopic experiments reveal electric-field-induced changes of the redox potentials also for the structurally very similar Cyt-c(3) from Desulfovibrio vulgaris, although the shifts are somewhat smaller compared to Cyt-c(3) 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.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal.
authors.forename: Laura
authors.initials: L
authors.lastname: Rivas
authors.forename: Cláudio M
authors.initials: CM
authors.lastname: Soares
authors.forename: António M
authors.initials: AM
authors.lastname: Baptista
authors.forename: Jalila
authors.initials: J
authors.lastname: Simaan
authors.forename: Roberto E
authors.initials: RE
authors.lastname: Di Paolo
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Murgida
authors.forename: Peter
authors.initials: P
authors.lastname: Hildebrandt
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D003574:Cytochrome c Group / Q000737:chemistry*; D045286:Desulfovibrio gigas / Q000737:chemistry; D016969:Desulfovibrio vulgaris / Q000737:chemistry; D005227:Fatty Acids / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D008567:Membranes, Artificial; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman; D055672:Static Electricity; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D003574:Cytochrome c Group; D005227:Fatty Acids; D008567:Membranes, Artificial; D006418:Heme; C017165:cytochrome c(3)