Functional Analysis of PsbR in PsbP Binding to Photosystem II

Abstract

The PsbP protein is a thylakoid lumenal extrinsic subunit of photosystem II (PSII) specifically found in green plants, such as higher plants and green algae. The binding site of PsbP in PSII has not been determined because of the lack of the high-resolution 3D structure of green plant PSII. Recent studies indicate that the PsbR protein, which is specific to higher plants, is involved in the PsbP binding to PSII; however, the role of PsbR has not been clarified yet. In this study, we showed that PsbR was fractionated differently from PsbP when thylakoid protein complexes were solubilized and separated by sucrose density gradient ultracentrifugation. On the other hand, PsbP was dissociated more easily from the thylakoid membranes in Arabidopsis mutant lacking PsbR than in the wild type, when thylakoid membranes were washed by low-pH buffers or high-NaCl containing buffers. These results suggest that PsbR is not essential but has an auxiliary role for the PsbP binding to PSII.