Complete amino acid sequence of the ubiquinone binding protein (QP-C), a protein similar to the 14,000-dalton subunit of the yeast ubiquinol-cytochrome c reductase complex.

S Wakabayashi,T Takao,Y Shimonishi,S Kuramitsu,H Matsubara,T Wang,Z Zhang,T E King

doi:10.1016/s0021-9258(18)89737-x

Abstract

The amino acid sequence of the ubiquinone binding protein (QP-C) in the cytochrome bc1 region of the mitochondrial electron transfer chain was determined by analysis of peptides obtained by cyanogen bromide cleavage and staphylococcal protease digestion of succinylated derivatives. It was found to consist of 110 amino acid residues and its amino terminus to be blocked by an acetyl group, as determined by mass spectrometry of the amino-terminal peptide and a comparison with peptides chemically synthesized on high-performance liquid chromatography. The molecular weight of this ubiquinone binding protein including the acetyl group was calculated to be 13,389. The predicted secondary structure of QP-C has alpha-helical content of about 50% and QP-C was classified as an "all-alpha" or "alpha + beta" protein. This is the first report describing the amino acid sequence of the ubiquinone binding protein. A comparison of this sequence with that of the 14-kDa subunit of the yeast ubiquinol-cytochrome c reductase complex from the nucleotide sequence showed these two sequences to be quite similar.

Highlights

From the +Department ofBiology, Faculty of Science, Osaka University, Toyomka, Osaka 560, Japan, the §Peptide Center, Institute for Protein Research, Osaka University, Suita, Osaka 565, Japan, the llDepartmentof Medical Chemistry, Osaka
The amino acid sequence of the ubiquinone binding of the polypeptides was performed by photoaffinity labeling protein(QP-C)inthecytochrome b c l region of the of the cytochrome bcl complex with arylazido ubiquinone mitochondrial electron transfer chainwas determined derivatives [8].Isolation of QP-C and reconstitution of the by analysis of peptides obtained by cyanogen bromideubiquinone-cytochrome c reductase have been accomcleavage and staphylococcal protease digestion of suc-plished [9].Chemicalcharacterization of the ubiquinone bindcinylated derivatives
It was found to consist of 110 ing protein is vital for understanding electron transfer aminoacidresiduesand its aminoterminustobe blocked byan acetyl group, as determined bymass spectrometry of the amino-terminal peptide and a parison with peptides chemically synthesizedon highperformanceliquidchromatography.Themolecular weight of this ubiquinone binding protein including the acetyl group was calculatedto be 13,389

Summary

AND RESULTS’

A comparison of this sequence with that of the 14-kDa subunitoftheyeastubiquinolcytochrome c reductase complex from the nucleotide sequence showed thesetwo sequences to be quite similar. The sequence was found to consist of 110 amino acid residues with no cysteine. The molecular weightof the sequence including the N-. Terminal acetyl group was calculated to be 13,389. Ubiquinone is an essential component of the mitochondrial electron transfer system [1, 2]. It exists as a hypothetical mobile component is molar excess compared to other electron

DISCUSSION

RESULTS

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