On the interaction of mitochondrial complex III with the Rieske iron-sulfur protein (subunit V).
Limited proteolysis of solubilized beef heart mitochondrial complex III with trypsin yields a product previously identified as fragment V" (González-Halphen, D., Lindorfer, M. A., and Capaldi, R. A. (1988) Biochemistry 27, 7021-7031). In this work, fragment V" was generated by trypsin treatment of both the intact complex III and the purified Rieske iron-sulfur protein. Thus, in its bound or isolated form, the same sites of subunit V are sensitive to protease action. Fragment V" was a soluble protein that retained its iron-sulfur moiety. It was purified by exclusion from a hydrophobic phenyl-Sepharose CL-4B column followed by gel filtration. In contrast to the pure, intact subunit V, fragment V" did not reconstitute oxidoreductase activity when combined with complex III devoid of subunit V. However, a 20-amino acid synthetic peptide carrying the sequence between amino acids Lys33 and Lys52 of the Rieske iron-sulfur protein competed with intact subunit V in reconstitution assays. The results obtained suggest that the iron-sulfur protein binds to complex III by hydrophobic protein-protein interactions, and that a nontransmembrane 18-amino acid amphipathic stretch accounts for the association of this subunit to the rest of the complex.
González-Halphen
D
D
Departamento de Bioenergética, Universidad Nacional Autónoma de México, México D.F.
Vázquez-Acevedo
M
M
García-Ponce
B
B
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D014450:Electron Transport Complex III / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000201:enzymology*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012689:Sequence Homology, Nucleic Acid; D014357:Trypsin
D007506:Iron-Sulfur Proteins; C037989:Rieske iron-sulfur protein; D014357:Trypsin; D014450:Electron Transport Complex III