An EPR spin label study of the quinol oxidase, E. coli cytochrome bo3: A search for redox induced conformational changes: A search for redox induced conformational changes

Gaye F. White, Sarah Field, Sophie Marritt, Vasily S. Oganesyan, Robert B. Gennis, Lai Lai Yap, Andromachi Katsonouri, Andrew J. Thomson

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Abstract

A search for conformational changes at the cytosolic entrance to the proton channels of the heme-copper quinol oxidase (QO), cytochrome bo3, E. coli, has been carried out using site directed nitroxide spin labeling (SDSL) of cysteine residues. These were positioned at R134 and R309, on loops that link helices II and III and VI and VII at the entrances to the D and K proton channels, respectively. The motional characteristics of both labels have been determined using X- and W-band EPR spectroscopy at room temperature in selected redox levels in the reaction sequence of QO with oxygen, namely, the mixed valence carbon monoxide form (COMV), the oxidized (O) and super-oxidized (P M) states. The O to PM step is accompanied by the uptake of protons through the K pathway. We find no evidence for changes in the motional characteristics of either label that are expected to be associated with helical motions at the entrances to the channels. Because kinetic studies of mutants show that the redox gating of protons occurs deep within the D channel close to the heme-copper site, the present study implies that no motion is transmitted to the ends of the helices.

Original languageEnglish
Pages (from-to)2355-2363
Number of pages9
JournalBiochemistry
Volume46
Issue number9
Early online date9 Feb 2007
DOIs
Publication statusPublished - 6 Mar 2007

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