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2bs4
From Proteopedia
GLU C180-> ILE VARIANT QUINOL:FUMARATE REDUCTASE FROM WOLINELLA SUCCINOGENES
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.
Experimental support for the "E pathway hypothesis" of coupled transmembrane e- and H+ transfer in dihemic quinol:fumarate reductase., Lancaster CR, Sauer US, Gross R, Haas AH, Graf J, Schwalbe H, Mantele W, Simon J, Madej MG, Proc Natl Acad Sci U S A. 2005 Dec 27;102(52):18860-5. PMID:16380425
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
About this Structure
2BS4 is a 6 chains structure of sequences from Wolinella succinogenes. Full crystallographic information is available from OCA.
Reference
- Lancaster CR, Sauer US, Gross R, Haas AH, Graf J, Schwalbe H, Mantele W, Simon J, Madej MG. Experimental support for the "E pathway hypothesis" of coupled transmembrane e- and H+ transfer in dihemic quinol:fumarate reductase. Proc Natl Acad Sci U S A. 2005 Dec 27;102(52):18860-5. PMID:16380425
Page seeded by OCA on Mon Feb 16 11:26:56 2009
Categories: Succinate dehydrogenase | Wolinella succinogenes | Lancaster, C R.D. | 2fe-2 | 3fe-4 | 4fe-4 | Citric acid cycle | Dihaem cytochrome b | Electron transport | Fad | Flavoprotein | Fumarate reductase | Heme | Ion-sulphur protein | Iron | Iron-sulfur | Metal-binding | Oxidoreductase | Respiratory chain | Transmembrane | Tricarboxylic acid cycle
