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Respiratory Complexes III and IV Can Each Bind Two Molecules of Cytochrome c at Low Ionic Strength

IBVF

Blas Moreno-Beltrán, Irene Díaz-Moreno, Katiuska González-Arzola, Alejandra Guerra-Castellano, Adrián Velázquez-Campoy, Miguel A. De la Rosa, Antonio Díaz-Quintana FEBS Letters 2015, Vol. 0, doi:10.1016/j.febslet.2015.01.004.

The transient interactions of respiratory cytochrome c with complexes III and IV is herein investigated by using heterologous proteins, namely human cytochrome c, the soluble domain of plant cytochrome c1 and bovine cytochrome c oxidase. The binding molecular mechanisms of the resulting cross-complexes have been analyzed by Nuclear Magnetic Resonance and Isothermal Titration Calorimetry. Our data reveal that the two cytochrome c-involving adducts possess a 2:1 stoichiometry – that is, two cytochrome c molecules per adduct – at low ionic strength. We conclude that such extra binding sites at the surfaces of complexes III and IV can facilitate the turnover and sliding of cytochrome c molecules and, therefore, the electron transfer within respiratory supercomplexes.