Identification of the residues involved in stabilization of the semiquinone radical in the high-affinity ubiquinone binding site in cytochrome bo3 from Escherichia coli by site-directed mutagenesis and EPR spectroscopy

Petra Hellwig, Takahiro Yano, Tomoko Ohnishi, Robert B. Gennis

Research output: Contribution to journalArticlepeer-review

Abstract

During turnover of cytochrome bo3 from Escherichia coli, a semiquinone radical is stabilized in a high-affinity binding site. To identify binding partners of this radical, site-directed mutants have been designed on the basis of a recently modeled quinone binding site (Abramson et al., 2000). The R71H, H98F, D75H, and I102W mutant enzymes were found to show very little or no quinol oxidase activity. The thermodynamic and EPR spectroscopic properties of semiquinone radicals in these mutants were characterized. For the H98F and the R71H mutants, no EPR signal of the semiquinone radical was observed in the redox potential range from - 100 to 250 mV. During potentiometric titration of the D75H mutant enzyme, a semiquinone signal was detected in the same potential range as that of the wild-type enzyme. However, the EPR spectrum of the D75H mutant lacks the characteristic hyperfine structure of the semiquinone radical signal observed in the wild-type oxidase, indicating that D75 or the introduced His, interacts with the semiquinone radical. For the I102W mutant, a free radical signal was observed with a redox midpoint potential downshifted by about 200 mV. On the basis of these observations, it is suggested that R71, D75, and H98 residues are involved in the stabilization of the semiquinone state in the high-affinity binding site. Details of the possible binding motif and mechanistic implications are discussed.

Original languageEnglish (US)
Pages (from-to)10675-10679
Number of pages5
JournalBiochemistry
Volume41
Issue number34
DOIs
StatePublished - Aug 27 2002

ASJC Scopus subject areas

  • Biochemistry

Fingerprint Dive into the research topics of 'Identification of the residues involved in stabilization of the semiquinone radical in the high-affinity ubiquinone binding site in cytochrome bo<sub>3</sub> from Escherichia coli by site-directed mutagenesis and EPR spectroscopy'. Together they form a unique fingerprint.

Cite this