Oxygenic photosystem II: the mutation D1-D61N in Synechocystis sp. PCC 6803 retards S-state transitions without affecting electron transfer from YZ to P680+.
Photosynthetic oxygen evolution is powered by photosystem II (PSII), in particular by the oxidized chl a-aggregate P680+, and catalyzed by the oxygen-evolving complex (Mn4X-entity) as well as a tyrosine residue (YZ). The role of particular amino acids as cofactors of electron and proton transfer or as modulators of the activity is still ill-defined. The effects of single-site mutations at the donor side of PSII on the partial reactions of water oxidation have been primarily studied in whole cells. Because of better signal-to-noise in oxygen-evolving core preparations more detailed information on the electronic, protonic, and electrostatic events is expected from studies with such material. We investigated cells and oxygen-evolving core preparations from the wildtype of Synechocystis sp. PCC 6803 and point-mutants of D1-D61. In cells, oxygen-release was slowed drastically in D61A (8-fold) and D61N (10-fold) compared to WT, whereas it remained unchanged in D61E within the time resolution of the measurements. In core preparations, the S1 --> S2 and S2 --> S3 transitions were slowed approximately 2-fold in D61N compared to WT. However, the nanosecond components of electron transfer from YZ to P680+ were unchanged in the same mutant. We conclude that substitution of a neutral residue for D1-D61 selectively affects electron-transfer events on the donor side of YZ.
Abt. Biophysik, Universität Osnabrück, Germany.
M
M
Hundelt
A M
AM
Hays
R J
RJ
Debus
W
W
Junge
D001216:Asparagine / Q000235:genetics*; D001224:Aspartic Acid / Q000235:genetics*; D002734:Chlorophyll / Q000378:metabolism*; D000458:Cyanobacteria / Q000737:chemistry / Q000235:genetics; D004579:Electron Transport; D008027:Light; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011048:Polarography; D013053:Spectrophotometry; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism
D045322:Photosynthetic Reaction Center Complex Proteins; C066447:tyrosyl radical Y(D); D002734:Chlorophyll; D001224:Aspartic Acid; D014443:Tyrosine; C025167:P-680; D001216:Asparagine; D010100:Oxygen