Electron paramagnetic resonance and mutational analyses revealed the involvement of photosystem II-L subunit in the oxidation step of Tyr-Z by P680+ to form the Tyr-Z+P680Pheo- state in photosystem II.
To reveal the molecular mechanism of involvement of photosystem II (PSII)-L protein in the electron transfer in PSII, effects of mutations in PSII-L on the photochemistry of PSII were investigated by means of electron paramagnetic resonance (EPR) and flash photolysis. Wild type and a series of mutant versions of PSII-L were overproduced in Escherichia coliand chromatographically purified. Plastoquinone 9 (PQ-9) depleted PSII reaction center core complex consisting of CP47/D1/D2/Cytb-559/PSII-I/PSII-W was prepared and reconstituted with the wild type and each mutant version of PSII-L together with or without PQ-9. EPR signal indicating the formation of Tyr-Z+P680Pheo- state upon room-temperature illumination disappeared in CP47/D1/D2/Cytb-559/PSII-I/PSII-W, and it was recovered when the complex was reconstituted with the wild-type PSII-L. Mutation of a few amino acid residues in the carboxyl-terminal region of PSII-L, such as substitution of a triad of Tyr34, Phe35, and Phe36 by Leu, selectively resulted in the loss of the capability of PSII-L to recover the light-induced formation of Tyr-Z+P680Pheo- state in the reconstituted complex. Hydropathy profile of PSII-L suggests that it spans the membrane once by a hydrophobic stretch of the carboxyl-terminal side as its carboxyl end to face to the lumen. If this is the case, the amino acid residues essential for PSII-L to function are expected to be located close to the donor side of P680, suggesting the interaction of PSII-L with Tyr-Z (and/or Tyr-D) or P680 to facilitate the oxidation of Tyr-Z by P680+ to form Tyr-Z+P680Pheo- state in PSII. Evidence against PSII-L being involved in the electron transfer from Pheo- to QA was obtained by the flash photolysis experiments.
Hoshida
H
H
Graduate School of Human and Environmental Studies, Kyoto University, Japan.
Sugiyama
R
R
Nakano
Y
Y
Shiina
T
T
Toyoshima
Y
Y
D000595:Amino Acid Sequence; D001483:Base Sequence; D004252:DNA Mutational Analysis; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010084:Oxidation-Reduction; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D018724:Spinacia oleracea; D014443:Tyrosine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014443:Tyrosine