Subsequent events to GTP binding by the plant PsbO protein: structural changes, GTP hydrolysis and dissociation from the photosystem II complex.
Besides an essential role in optimizing water oxidation in photosystem II (PSII), it has been reported that the spinach PsbO protein binds GTP [C. Spetea, T. Hundal, B. Lundin, M. Heddad, I. Adamska, B. Andersson, Proc. Natl. Acad. Sci. U.S.A. 101 (2004) 1409-1414]. Here we predict four GTP-binding domains in the structure of spinach PsbO, all localized in the beta-barrel domain of the protein, as judged from comparison with the 3D-structure of the cyanobacterial counterpart. These domains are not conserved in the sequences of the cyanobacterial or green algae PsbO proteins. MgGTP induces specific changes in the structure of the PsbO protein in solution, as detected by circular dichroism and intrinsic fluorescence spectroscopy. Spinach PsbO has a low intrinsic GTPase activity, which is enhanced fifteen-fold when the protein is associated with the PSII complex in its dimeric form. GTP stimulates the dissociation of PsbO from PSII under light conditions known to also release Mn(2+) and Ca(2+) ions from the oxygen-evolving complex and to induce degradation of the PSII reaction centre D1 protein. We propose the occurrence in higher plants of a PsbO-mediated GTPase activity associated with PSII, which has consequences for the function of the oxygen-evolving complex and D1 protein turnover.
Lundin
Björn
B
Division of Cell Biology, Linköping University, SE-581 85 Linköping, Sweden.
Thuswaldner
Sophie
S
Shutova
Tatiana
T
Eshaghi
Said
S
Samuelsson
Göran
G
Barber
James
J
Andersson
Bertil
B
Spetea
Cornelia
C
D000595:Amino Acid Sequence; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism
D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C054266:photosystem II manganese-stabilizing protein; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D010100:Oxygen