Experimental Support for the E-Pathway Hypothesis of Coupled Transmembrane Electron and Proton Transfer in Dihemic Quinol:Fumarate ReductaseLancaster, C.R.D., Sauer, U.S., Gross, R., Haas, A.H., Graf, J., Schwalbe, H., Maentele, W., Simon, J., Madej, G.
(2005) Proc Natl Acad Sci U S A 102: 18860
- PubMed: 16380425
- DOI: 10.1073/pnas.0509711102
- Primary Citation of Related Structures:
- PubMed Abstract:
- Wolinella Succinogenes Quinol:Fumarate Reductase and its Comparison to E. Coli Succinate:Quinone Reductase
(2003) FEBS Lett 555: 21
- Wolinella Succinogenes Quinol:Fumarate Reductase -2.2 Angstrom Resolution Crystal Structure and the E-Pathway Hypothesis of Coupled Transmembrane Proton and Electron Transfer
(2002) Biochim Biophys Acta 1565: 215
- A Third Crystal Form of Wolinella Succinogenes Quinol:Fumarate Reductase Reveals Domain Closure at the Site of Fumarate Reduction
Lancaster, C.R.D., Gross, R., Simon, J.
(2001) Eur J Biochem 268: 1820
- Essential Role of Glu-C66 for Menaquinol Oxidation Indicates Transmembrane Electrochemical Potential Generation by Wolinella Succinogenes Fumarate Reductase
Lancaster, C.R.D., Gross, R., Haas, A., Ritter, M., Maentele, W., Simon, J., Kroeger, A.
(2000) Proc Natl Acad Sci U S A 97: 13051
- Structure of Fumarate Reductase from Wolinella Succinogenes at 2.2 Angstroms Resolution
Lancaster, C.R.D., Kroeger, A., Auer, M., Michel, H.
(1999) Nature 402: 377
Reconciliation of apparently contradictory experimental results obtained on the quinol:fumarate reductase, a diheme-containing respiratory membrane protein complex from Wolinella succinogenes, was previously obtained by the proposal of the so-called "E pathway hypothesis ...
Reconciliation of apparently contradictory experimental results obtained on the quinol:fumarate reductase, a diheme-containing respiratory membrane protein complex from Wolinella succinogenes, was previously obtained by the proposal of the so-called "E pathway hypothesis." According to this hypothesis, transmembrane electron transfer via the heme groups is strictly coupled to cotransfer of protons via a transiently established pathway thought to contain the side chain of residue Glu-C180 as the most prominent component. Here we demonstrate that, after replacement of Glu-C180 with Gln or Ile by site-directed mutagenesis, the resulting mutants are unable to grow on fumarate, and the membrane-bound variant enzymes lack quinol oxidation activity. Upon solubilization, however, the purified enzymes display approximately 1/10 of the specific quinol oxidation activity of the wild-type enzyme and unchanged quinol Michaelis constants, K(m). The refined x-ray crystal structures at 2.19 A and 2.76 A resolution, respectively, rule out major structural changes to account for these experimental observations. Changes in the oxidation-reduction heme midpoint potential allow the conclusion that deprotonation of Glu-C180 in the wild-type enzyme facilitates the reoxidation of the reduced high-potential heme. Comparison of solvent isotope effects indicates that a rate-limiting proton transfer step in the wild-type enzyme is lost in the Glu-C180 --> Gln variant. The results provide experimental evidence for the validity of the E pathway hypothesis and for a crucial functional role of Glu-C180.
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, D-60438 Frankfurt am Main, Germany. email@example.com