Domain movement of iron sulfur protein in cytochrome bc₁ complex is facilitated by the electron transfer from cytochrome b_L to b_H

Abstract 

The key step of the “protonmotive Q-cycle” mechanism for cytochrome bc₁ complex is the bifurcated oxidation of ubiquinol at the Qp site. ISP is reduced when its head domain is at the b-position and subsequent move to the c₁ position, to reduce cytochrome c₁, upon protein conformational changes caused by the electron transfer from cytochrome b_L to b_H. Results of analyses of the inhibitory efficacy and the binding affinity, determined by isothermal titration calorimetry, of Pm and Pf, on different redox states of cytochrome bc₁ complexes, confirm this speculation. Pm inhibitor has a higher affinity and better efficacy with the cytochrome b_H reduced complex and Pf binds better and has a higher efficacy with the ISP reduced complex.

Abbreviations: bc₁, the cytochrome bc₁ complex, b_L, low potential cytochrome b, b_H, high-potential cytochrome b, ISP, iron–sulfur protein, Qp, quinol oxidation site, Qn, quinol reduction site, Pm, Qp inhibitors that facilitate the ISP head domain movement, Pf, Qp inhibitors that fix the ISP head domain at the b-position, MOAS, (E)-β-methoxyacrylate-stilbene, Stig, stigmatellin, DM, N-dodecyl-β-d-maltoside, QH₂, ubiquinol and Q₀C₁₀BrH₂, 2,3-dimethoxy-5-methyl-6-(10-bromodecyl)-1,4-benzoquinol

Keywords: Cytochrome bc₁ complex, Iron–sulfur protein, MOA-stilbene, Stigmatellin