Functional dissection of two Arabidopsis PsbO proteins: PsbO1 and PsbO2.
PsbO protein is an extrinsic subunit of photosystem II (PSII) and has been proposed to play a central role in stabilization of the catalytic manganese cluster. Arabidopsis thaliana has two psbO genes that express two PsbO proteins; PsbO1 and PsbO2. We reported previously that a mutant plant that lacked PsbO1 (psbo1) showed considerable growth retardation despite the presence of PsbO2 [Murakami, R., Ifuku, K., Takabayashi, A., Shikanai, T., Endo, T., and Sato, F. (2002) FEBS Lett523, 138-142]. In the present study, we characterized the functional differences between PsbO1 and PsbO2. We found that PsbO1 is the major isoform in the wild-type, and the amount of PsbO2 in psbo1 was significantly less than the total amount of PsbO in the wild-type. The amount of PsbO as well as the efficiency of PSII in psbo1 increased as the plants grew; howeVER, it neVER reached the total PsbO level observed in the wild-type, suggesting that the poor activity of PSII in psbo1 was caused by a shortage of PsbO. In addition, an in vitro reconstitution experiment using recombinant PsbOs and urea-washed PSII particles showed that oxygen evolution was better recoVERed by PsbO1 than by PsbO2. Further analysis using chimeric and mutated PsbOs suggested that the amino acid changes Val186-->Ser, Leu246-->Ile, and Val204-->Ile could explain the functional difference between the two PsbOs. Therefore we concluded that both the lower expression level and the inferior functionality of PsbO2 are responsible for the phenotype observed in psbo1.
Murakami
Reiko
R
Division of Integrated Life Sciences, Graduate School of Biostudies, Kyoto University, Kyoto, Japan.
Ifuku
Kentaro
K
Takabayashi
Atsushi
A
Shikanai
Toshiharu
T
Endo
Tsuyoshi
T
Sato
Fumihiko
F
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
D029681:Arabidopsis Proteins; D045332:Photosystem II Protein Complex; D020033:Protein Isoforms; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D010100:Oxygen