title: Effect of a pH Gradient on the Protonation States of Cytochrome c Oxidase: A Continuum Electrostatics Study.
abstract: Cytochrome c oxidase (CcO) couples the reduction of dioxygen to water with transmembrane proton pumping, which leads to the generation of an electrochemical gradient. In this study we analyze how one of the components of the electrochemical gradient, the difference in pH across the membrane, or ΔpH, influences the protonation states of residues in CcO. We modified our continuum electrostatics/Monte Carlo (CE/MC) method in order to include the ΔpH and applied it to the study of CcO, in what is, to our best knowledge, the first CE/MC study of CcO in the presence of a pH gradient. The inclusion of a transmembrane pH gradient allows for the identification of residues whose titration behavior depends on the pH on both sides of the membrane. Among the several residues with unusual titration profiles, three are well-known key residues in the proton transfer process of CcO: E286I, Y288I, and K362I. All three residues have been previously identified as being critical for the catalytic or proton pumping functions of CcO. Our results suggest that when the pH gradient increases, these residues may be part of a regulatory mechanism to stem the proton flow.
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa , 2781-901 Oeiras, Portugal.
authors.forename: Pedro R
authors.initials: PR
authors.lastname: Magalhães
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa , 2781-901 Oeiras, Portugal.
authors.forename: A Sofia F
authors.initials: AS
authors.lastname: Oliveira
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa , 2781-901 Oeiras, Portugal.
authors.forename: Sara R R
authors.initials: SR
authors.lastname: Campos
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa , 2781-901 Oeiras, Portugal.
authors.forename: Cláudio M
authors.initials: CM
authors.lastname: Soares
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa , 2781-901 Oeiras, Portugal.
authors.forename: António M
authors.identifier: 0000-0002-7044-1210
authors.initials: AM
authors.lastname: Baptista
mesh_terms: D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011522:Protons; D012242:Rhodobacter sphaeroides / Q000201:enzymology; D055672:Static Electricity
chemical_list: D011522:Protons; D003576:Electron Transport Complex IV