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.USA 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
- 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.USA 97: 13051
- 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
- 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 ...
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.
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