title: Evidence for transmembrane proton transfer in a dihaem-containing membrane protein complex.
abstract: Membrane protein complexes can support both the generation and utilisation of a transmembrane electrochemical proton potential ('proton-motive force'), either by transmembrane electron transfer coupled to protolytic reactions on opposite sides of the membrane or by transmembrane proton transfer. Here we provide the first evidence that both of these mechanisms are combined in the case of a specific respiratory membrane protein complex, the dihaem-containing quinol:fumarate reductase (QFR) of Wolinella succinogenes, so as to facilitate transmembrane electron transfer by transmembrane proton transfer. We also demonstrate the non-functionality of this novel transmembrane proton transfer pathway ('E-pathway') in a variant QFR where a key glutamate residue has been replaced. The 'E-pathway', discussed on the basis of the 1.78-Angstrom-resolution crystal structure of QFR, can be concluded to be essential also for the viability of pathogenic epsilon-proteobacteria such as Helicobacter pylori and is possibly relevant to proton transfer in other dihaem-containing membrane proteins, performing very different physiological functions.
authors.affiliation: Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: M Gregor
authors.initials: MG
authors.lastname: Madej
authors.forename: Hamid R
authors.initials: HR
authors.lastname: Nasiri
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Hilgendorff
authors.forename: Harald
authors.initials: H
authors.lastname: Schwalbe
authors.forename: C Roy D
authors.initials: CR
authors.lastname: Lancaster
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D018360:Crystallography, X-Ray / Q000379:methods; D004579:Electron Transport / Q000235:genetics; D016480:Helicobacter pylori / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017494:Proton Pumps / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011522:Protons; D013045:Species Specificity; D016968:Wolinella / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D017494:Proton Pumps; D011522:Protons; D010088:Oxidoreductases; C424907:quinol fumarate reductase