Cross-linking of the D1 protein with the surrounding polypeptides in PS II and digestion of the cross-linked products by a stromal protease(s) comprise a crucial pathway of D1 turnover during photoinhibition of PS II

Abstract

Both the donor-side and acceptor-side photoinhibition of PS II induce significant cross-linking of the D1 protein with the surrounding polypeptides. The cross-linked products, i.e. D1/D2, D1/the a-subunit of cytochrome b559 and D1/CP43, are generated depending on the mechanism of photoinhibition (donor-side or acceptor-side), samples used, light intensity and illumination period. Quantitative analyses of the fluorogram obtained after SDS/urea-PAGE and Western blotting, showed that the amount of the cross-linked products goes up to over 30% of the total D1 protein under strong illumination of PS II samples. The cross-linked products produced by the acceptor-side photoinhibition are degraded efficiently by a stromal protease(s). From these results, we propose that the formation and degradation of the D1 cross-linked products form a crucial pathway for efficient turnover of the photodamaged D1 protein. The protease(s) recognizing the cross-linked products as substrates in the stroma was characterized. Purification of the protease(s) is now being undertaken.