Chlorophyll a is the crucial redox sensor and transmembrane signal transmitter in the cytochrome b 6 f complex. Components and mechanisms of state transitions from the hydrophobic mismatch viewpoint

However, the components and molecular mechanisms are still unclear. In an attempt to solve this long-standing problem, we first focused on the unknown role of a single chlorophyll a (Chl a ) in cyt b 6 f with a new approach based on Chl a structural properties.

Various b 6 f X-ray crystal structures were analyzed to identify their differences, which correlate with differences in Chl a molecular volume. We found that the distance of the Rieske [2Fe-2S] cluster to Chl a correlates with the distance between a pair of residues at the Q o -site and the distance between a pair of residues at the opposite membrane side. These correlations were accompanied by the rotation of a key peripheral residue and by changes in the hydrophobic thickness of cyt b 6 f .