Protein conformational changes involved in the cytochrome bc1 complex catalytic cycle

• The soluble portion of the iron sulfur subunit is known to acts as conformationally assisted electron transfer mechanism.
• The known mechanics for how the translational and rotational movements of this domain occur are outlined.
• Multiple instances of control over the equilibrium position the cytochrome bc1 complex FeS domain are outlined.

Early structures of the cytochrome bc1 complex revealed heterogeneity in the position of the soluble portion of the Rieske iron sulfur protein subunit, implicating a movement of this domain during function. Subsequent biochemical and biophysical works have firmly established that the motion of this subunit acts in the capacity of a conformationally assisted electron transfer step during the already complicated catalytic mechanism described within the modified version of Peter Mitchells Q cycle. How the movement of this subunit is initiated or how the frequency of its motion is controlled as a function of other steps during the catalysis remain topics of debate within the active research communities. This review addresses the historical aspects of the discovery and description of this movement, while attempting to provide a context for the involvement of conformational motion in the catalysis and efficiency of the enzyme. This article is part of a Special Issue entitled: Respiratory complex III and related bc complexes.