title: Evidence that the PsbK polypeptide is associated with the photosystem II core antenna complex CP43.
abstract: PsbK is encoded by the chloroplast psbK gene and is one of the small polypeptides of photosystem II (PSII). This polypeptide is required for accumulation of the PSII complex. In the present study, we generated an antibody against recombinant mature PsbK of Chlamydomonas and used it in Western blots to localize PsbK in the PSII core complex. PsbK was found in the thylakoid membranes, and purification of the PSII core complex from detergent-solubilized thylakoid membranes showed that PsbK is tightly associated with the PSII core complex. We used potassium thiocyanate to separate PSII into subcore complexes, including the D1/D2/cytochrome b559 reaction center complex, CP47, and CP43, and we found that PsbK co-purifies with one of the core antenna complexes, CP43, during ion exchange chromatography. Subsequent gel filtration chromatography of the purified CP43 confirmed that PsbK is tightly associated with CP43. Steady-state levels of PsbK were also determined in Chlamydomonas mutants expressing various levels of PSII. Quantitative Western blotting revealed that the levels of PsbK in these mutants are approximately equal to those of CP43, suggesting that PsbK is stable only when associated with CP43 in the chloroplast. Together, our results indicate that PsbK is an integral part of the PSII complex and may participate in the assembly and stability of the PSII complex.
authors.affiliation: Department of Biology, Faculty of Science, Okayama University, Tsushima-naka, Okayama 700-8530, Japan.
authors.forename: Ikuyo
authors.initials: I
authors.lastname: Sugimoto
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Takahashi
mesh_terms: D020418:Algal Proteins / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002499:Centrifugation, Density Gradient; D002696:Chlamydomonas / Q000737:chemistry / Q000235:genetics; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003573:Cytochrome b Group / Q000302:isolation & purification; D045342:Light-Harvesting Protein Complexes / Q000302:isolation & purification; D009154:Mutation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D045332:Photosystem II Protein Complex / Q000032:analysis* / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D015800:Protozoan Proteins / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism; D013861:Thiocyanates; D020524:Thylakoids / Q000737:chemistry
chemical_list: D020418:Algal Proteins; D003573:Cytochrome b Group; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D015800:Protozoan Proteins; D013861:Thiocyanates; C083100:photosystem II, chlorophyll binding protein, CP-43; C070970:photosystem II, chlorophyll-binding protein, CP-47; C019313:cytochrome b559; C009941:potassium thiocyanate