Poster: Photosynthesis

Abs # 357: The effect of GTP on the D1 protein degradation under heat stress

Presenter:	Uchida, Suguru , s-uchidarkness@mail.goo.ne.jp
Authors	Uchida, Suguru  (A)   Yamamoto, Yasusi  (A)
Affiliations:	(A): Graduate School of Natural Science and Technology, Okayama University

When illuminated with excessive light, the reaction center-binding protein D1 in photosystem (PS) II is damaged and cleaved by a serine-type protease in a GTP-dependent manner. Until now, however, it is not known exactly why GTP facilitates the primary cleavage of the D1 protein. To study the role of GTP in the D1 protein degradation in detail, we examined the effect of GTP on the D1 degradation under heat stress using spinach thylakoids and PS II membranes. The thylakoids were treated at 37 ^oC for 30 min with or without GTP. In the presence of GTP, we observed a significant increase in the degradation of D1 protein. The effects of GTP were not observed with the PS II membranes, indicating the absence of the protease(s) that recognizes the damaged D1 protein in the PS II membranes. There are two possibilities for the effects of GTP on the D1 degradation. One is activation of the endogenous protease that is responsible for the primary cleavage of the D1 protein, and the other is the conformational change of the D1 protein by GTP binding to the thylakoid membranes. We discuss a possible role of GTP on the D1 degradation based on the experiments carried out under various in vitro conditions.