Photosystem II (PSII), an essential component of oxygenic photosynthesis, is a membrane-bound pigment protein complex found in green plants and cyanobacteria. Whereas the molecular structure of cyanobacterial PSII has been resolved with at least medium resolution [Zouni, A., Witt, ., Kern, J., Fromme, P., Krauss, N., Saenger, W. & Orth, P. (2001)Nature (London)409, 739–743; Kamiya, N. &Shen, . (2003)Proc. Natl Acad. Sci. USA100, 98–103], the structure of higher plant PSII is only known at low resolution. .
