2BS4

GLU C180 -> ILE VARIANT QUINOL:FUMARATE REDUCTASE FROMWOLINELLA SUCCINOGENES

Summary for 2BS4

• Entry DOI: 10.2210/pdb2bs4/pdb
• Related: 1E7P 1QLA 1QLB 2BS2 2BS3
• Descriptor: QUINOL-FUMARATE REDUCTASE FLAVOPROTEIN SUBUNIT A, IRON/SULFUR CLUSTER, DODECYL-BETA-D-MALTOSIDE, ... (13 entities in total)
• Functional Keywords: 2fe-2s, 3fe-4s, 4fe-4s, citric acid cycle, dihaem cytochrome b, electron transport, fad, flavoprotein, fumarate reductase, heme, ion-sulphur protein, iron, iron-sulfur, metal-binding, oxidoreductase, respiratory chain, succinate dehydrogenase, transmembrane, tricarboxylic acid cycle
• Biological source: WOLINELLA SUCCINOGENES; More
• Cellular location: Cell membrane; Multi-pass membrane protein: P17413
• Total number of polymer chains: 6
• Total formula weight: 267038.65

Authors

Lancaster, C.R.D. (deposition date: 2005-05-14, release date: 2005-12-13, Last modification date: 2024-11-20)

Primary citation

Lancaster, C.R.D.,Sauer, U.S.,Gross, R.,Haas, A.H.,Graf, J.,Schwalbe, H.,Maentele, W.,Simon, J.,Madej, G.
Experimental Support for the E-Pathway Hypothesis of Coupled Transmembrane Electron and Proton Transfer in Dihemic Quinol:Fumarate Reductase
Proc.Natl.Acad.Sci.USA, 102:18860-, 2005

PubMed Abstract: 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.

PubMed: 16380425
DOI: 10.1073/PNAS.0509711102

Experimental method

X-RAY DIFFRACTION (2.76 Å)