Study of Interactions between Huge Membrane Proteins and Soluble Proteins —Application to Photosynthetic Proteins—

In the photosynthetic light reactions of plants and cyanobacteria, plastocyanin plays a crucial role as an electron carrier and shuttle protein between two membrane protein complexes: cytochrome b6f and photosystem I. Using transferred cross-saturation method, we demonstrated that the hydrophobic patch residues of plastocyanin are in close proximity to PSI and cytochrome b6f, whereas the acidic patch residues of plastocyanin do not form stable salt bridges with either PSI or cyt b6f, in the electron transfer complexes. The transient characteristics of the interactions on the acidic patch facilitate the rapid association and dissociation of plastocyanin.