Abstract
The reaction center-binding protein D1 of Photosystem II (PSII) is damaged by high temperature or excessive visible light. The damaged D1 protein is degraded and removed from PSII or form aggregates with other PSII subunits.
When the thylakoids membranes from WT of a cyanobacterium Synechocystis sp.PCC6803 were illuminated, degradation and aggregation of the D1 protein were observed. Whereas degradation of the D1 protein was not detected in the thylakoids from the lacking of FtsH (slr0228) mutant, and D1 aggregation became prominent in these thylakoids. When the thylakoids with an increased level of FtsH obtained from low temperature-treated WT cells were illuminated with strong light, the D1 aggregates were less significant compared with the WT thylakoids. From these results, it is suggested that the FtsH proteases play a dual role as a protease for D1 degradation and a molecular chaperone to prevent accumulation of the D1 aggregates.
