2bs3
GLU C180 -> GLN VARIANT QUINOL:FUMARATE REDUCTASE FROM WOLINELLA SUCCINOGENES
Structural highlights
FunctionFRDA_WOLSU The fumarate reductase enzyme complex is required for fumarate respiration using formate or sulfide as electron donor. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedReconciliation 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[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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