CHANGES IN THE ORGANIZATION OF PHOTOSYSTEM-II FOLLOWING LIGHT-INDUCED D1-PROTEIN DEGRADATION

The composition and organization of photosystem II was studied in thylakoid membranes and subfractions which had been subjected to photoinhibitory light conditions. The results show that D1-protein degradation can occur in vitro leading to a 50-60% loss of the protein. Apart from the D2-protein, which shows a limited decline, there was no loss of any other photosystem II proteins. The D1-protein degradation induced several changes in the organization of the photosystem II complex. Using inside-out thylakoid vesicles we demonstrate that concomitant with the D1-protein degradation there is a release of the extrinsic 33, 23 and 16 kDa proteins from the inner thylakoid surface into the lumenal space. In addition, there is a release of four manganese ions per D1-protein degraded. The correlation between the D1-protein degradation and the release of manganese is also seen in inside-out thylakoid vesicles that have been CaCl2-washed to remove the three extrinsic proteins prior to photoinhibitory illumination. Subfractionation of thylakoids subsequent to photoinhibitory treatment suggests a migration of certain photosystem II subunits from the appressed to the non-appressed thylakoid regions following D1-protein degradation. The photosystem II subunits showed an individual migration behaviour, suggesting a disassembly of the photosystem II core. Our data suggest that repair of photodamaged photosystem II involves, apart from reinsertion of new D1-proteins, reassembly of the photosystem II complex including lateral movement of proteins between the two thylakoid regions and religation of the manganese cluster. © 1990.