| Budget Amount *help |
¥3,950,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥450,000)
Fiscal Year 2007: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
Fiscal Year 2006: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
Photosystem II (PSII) is the target of various abiotic stresses including excess visible light and high temperature. The reaction center Dl protein of PSII is damaged easily under these stresses and the damaged protein is either degraded by a specific protease(s) or forms aggregates with the nearby polypeptides such as D2 protein or CP43. In the present study, we analyzed the details of the degradation and aggregation pathways of the light-or heat-damaged Dl protein, using spinach thylakoids and the cyanobacterium Synechocystis PCC6803. The main points are as follows:
(1) When spinach thylakoids were heat-stressed (40℃ for 30 min), the D1 protein was damaged and the damaged D1 protein was degraded by FtsH proteases. We demonstrated the action of FtsH proteases by the solubilization and reconstitution experiments of FtsH.
(2) We found that heat stress induces reactive oxygen species, such as singlet oxygen and hydroxyl radicals near PSII. We also hind that under the heat stress, not only the D1 protein but also D2, PsbO and PsbQ proteins are oxidatively damaged. PsbO and other extrinsic proteins were released from PSII under the heat stress. As heat stress induced significant lipid peroxidation near PSII, we speculate that the heat-induced lipid peroxidation is related to the damage to PSII.
(3) In the mutant of Synechocystis PCC6803 lacking FtsH (slr0228), excess light induced significant aggregation of the D1 protein, compared with the wild-type cells. These results indicate that the FtsH protease degrades the D1 aggregates, or alternatively that the FtsH protease acts as a molecular chaperone to avoid protein aggregation. We are continuing the study using other protease mutants as well.
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