title: Modeling gating charge and voltage changes in response to charge separation in membrane proteins.
abstract: Measurements of voltage changes in response to charge separation within membrane proteins can offer fundamental information on mechanisms of charge transport and displacement processes. A recent example is provided by studies of cytochrome c oxidase. However, the interpretation of the observed voltage changes in terms of the number of charge equivalents and transfer distances is far from being trivial or unique. Using continuum approaches to describe the voltage generation may involve significant uncertainties and reliable microscopic simulations are not yet available. Here, we attempt to solve this problem by using a coarse-grained model of membrane proteins, which includes an explicit description of the membrane, the electrolytes, and the electrodes. The model evaluates the gating charges and the electrode potentials (c.f. measured voltage) upon charge transfer within the protein. The accuracy of the model is evaluated by a comparison of measured voltage changes associated with electron and proton transfer in bacterial photosynthetic reaction centers to those calculated using our coarse-grained model. The calculations reproduce the experimental observations and thus indicate that the method is of general use. Interestingly, it is found that charge-separation processes with different spatial directions (but the same distance perpendicular to the membrane) can give similar observed voltage changes, which indicates that caution should be exercised when using simplified interpretation of the relationship between charge displacement and voltage changes.
authors: Department of Chemistry, University of Southern California, Los Angeles, CA 90089;
authors: Ilsoo
authors: I
authors: Kim
authors: Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411008, India; and.
authors: Suman
authors: S
authors: Chakrabarty
authors: Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
authors: Peter
authors: P
authors: Brzezinski
authors: Department of Chemistry, University of Southern California, Los Angeles, CA 90089; warshel@usc.edu.
authors: Arieh
authors: A
authors: Warshel
mesh_terms: D004560:Electricity; D004566:Electrodes; D015640:Ion Channel Gating; D007834:Lasers; D008055:Lipids / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D008055:Lipids; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins
keywords: bacterial reaction center; electrogenicity; membrane potential; proton/electron transfer