Calcium ligation in photosystem II under inhibiting conditions.
In oxygenic photosynthesis, PSII carries out the oxidation of water and reduction of plastoquinone. The product of water oxidation is molecular oxygen. The water splitting complex is located on the lumenal side of the PSII reaction center and contains manganese, calcium, and chloride. Four sequential photooxidation reactions are required to generate oxygen from water; the five sequentially oxidized forms of the water splitting complex are known as the Sn states, where n refers to the number of oxidizing equivalents stored. Calcium plays a role in water oxidation; removal of calcium is associated with an inhibition of the S state cycle. Although calcium can be replaced by other cations in vitro, only strontium maintains activity, and the steady-state rate of oxygen evolution is decreased in strontium-reconstituted PSII. In this article, we study the role of calcium in PSII that is limited in water content. We report that strontium substitution or 18OH2 exchange causes conformational changes in the calcium ligation shell. The conformational change is detected because of a perturbation to calcium ligation during the S1 to S2 and S2 to S3 transition under water-limited conditions.
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, USA. bridgette.barry@chemistry.gatech.edu
Bridgette A
BA
Barry
Charles
C
Hicks
Antonio
A
De Riso
David L
DL
Jenson
D001665:Binding Sites; D001703:Biophysics / Q000379:methods; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004591:Electrophoresis, Polyacrylamide Gel; D008024:Ligands; D046911:Macromolecular Substances / Q000737:chemistry; D008280:Magnetics; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D010971:Plastoquinone / Q000737:chemistry; D011485:Protein Binding; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea / Q000378:metabolism; D013324:Strontium / Q000737:chemistry; D014867:Water / Q000737:chemistry
D008024:Ligands; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; D010971:Plastoquinone; D010100:Oxygen; D002118:Calcium; D013324:Strontium