Abstract
When spinach thylakoids were treated with heat (40oC for 30 min), the D1 protein of PS II was cleaved and a 23 kDa N-terminal fragment was produced. The proteolysis was specific to the D1 protein and no other proteins around the D1 protein were degraded. The cleavage of the D1 protein was stimulated by the addition of Zn and inhibited by EDTA, indicating participation of a metallo-protease. The protease was solubilized by washing thylakoids with 2M KSCN. The protease activity was detected by gelatin-activity gel electrophoresis at about 70 kDa region. Western blot analysis using antibody against FtsH protease (anti-DS9 and anti-VAR2) showed that the supernatant of KSCN-washed thylakoids contains an FtsH protease. Reconstitution of the FtsH protease with the thylakoids was also successfully carried out. These results suggest that the FtsH protease is responsible for the proteolysis of the D1 protein under heat stress.
