Abstract
Recent progress in structural biology has provided the structural information about photosystem II (PSII) complex. Some of the structures of extrinsic proteins in PSII were also reported, whereas such information is not available about PsbP, an extrinsic subunit of the water-oxidizing complex. PsbP specifically exists in PSII from higher plants and green algae, but not in that from cyanobacteria. It is thus a mystery how and why PsbP evolved for PSII in higher plants and green algae. We report here the crystal structure of PsbP from Nicotiana tabacum at a resolution of 1.6 Å.The structure of PsbP was mainly composed of β-sheet, and was not similar to any structures in cyanobacterial PSII. This suggests that higher plants and green algae obtained a structurally unrelated protein as an extrinsic protein during the evolution of PSII. The molecular evolution and the novel function of PsbP will be discussed.
