Anovel degradation pathway of the D1 protein under light stress

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Under light stress conditions, the reaction center binding D1 protein of photosystem II is degraded rapidly. In the present study, we found a novel pathway of D1 degradation. We characterized the pathway in detail and also studied the components involved in the pathway. The main results obtained are as follows :1. Isolation of a protease(s) degrading the cross-linked products of the D1 protein from the stioma : During the photoinhibition of photosystem II, the D1 protein cross-links with the surrounding polypeptides. We partiafly purified a protease(s) that recognizes and digests the cross-linked products from the fraction of stroma, using a gelatin activity gel.2. Determination of spatial arrangement of the D1 protein and neighboring polypeptides in photosystem II with the use of phofco-crossnnking reaction : We determined the relative arrangement of the D1 protein, CP43 andOEC33.in the lumenal side of photosystem II. These proteins are essential for the oxygen evolving activity of photosystem II, and the information obtained here is crucial for the structural analysis of the oxygen evolving system.3. Induction of singlet oxygen under heat and light stresses in photosystem II and the generation of cross-linked products of the D1 protein with the neighboring polypeptides : We found that formation of singlet oxygen by the illumination of PS II is stimulated under heat stress. The singlet oxygen was the main cause for the protein cross-linking in photosystem II.