Chemical crosslinking studies of extrinsic proteins in cyanobacterial photosystem II

Chemical crosslinking with a zero-length crosslinker, 1-ethyl-3-(3-dimethylaminopropyl) carbodimide hydrochloride, was applied to a cyanobacterial photosystem II complex retaining three extrinsic proteins, the 33 kDa manganese-stabilizing protein, cytochrome (cyt) c-550 and the 12 kDa protein. Three major crosslinked products were obtained in addition to the crosslinked product between the extrinsic 33 kDa and the intrinsic CP47 proteins. They were identified to be: cyt c-550-12 kDa; cyt c-550-12 kDa-33 kDa; D2-cyt c-550-12 kDa. These results indicate that the three extrinsic proteins are closely located with each other in cyanobacterial PSII, supporting the previous proposal that, like the 33 kDa protein, cyt c-550 and the 12 kDa protein are associated with PSII at the lumenal side of thylakoids. The results also suggested that the D2 reaction center protein provides a direct binding site for the extrinsic cyt c-550.