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| {{STRUCTURE_2bs3| PDB=2bs3 | SCENE= }} | | {{STRUCTURE_2bs3| PDB=2bs3 | SCENE= }} |
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| '''GLU C180-> GLN VARIANT QUINOL:FUMARATE REDUCTASE FROM WOLINELLA SUCCINOGENES'''
| | ===GLU C180-> GLN VARIANT QUINOL:FUMARATE REDUCTASE FROM WOLINELLA SUCCINOGENES=== |
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| ==Overview==
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| 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.
| | The line below this paragraph, {{ABSTRACT_PUBMED_16380425}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 16380425 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_16380425}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Transmembrane]] | | [[Category: Transmembrane]] |
| [[Category: Tricarboxylic acid cycle]] | | [[Category: Tricarboxylic acid cycle]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 20:43:19 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Jul 27 15:37:06 2008'' |
