Poster: Lipids & Related Molecules

Abs # 861: Contribution of sulfoquinovosyl diacylglycerol to the structural integrity and heat-tolerance of PSII complex

Presenter:	Sato, Norihiro , nsato@ls.toyaku.ac.jp
Authors	Sato, Norihiro  (A)   Aoki, Motohide  (A)   Maru, Yukihiro  (A)   Sonoike, Kintake  (B)   Minoda, Ayumi  (A)   Tsuzuki, Mikio  (A)
Affiliations:	(A): School of Life Science, Tokyo University of Pharmacy and Life Science (B): Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo

We have shown that sulfoquinovosyl diacylglycerol (SQDG), one of chloroplast-specific lipids, is bound to PSII complex for normal activity of the complex through analysis of a mutant of Chlamydomonas reinhardtii defective in SQDG (1, 2). To examine the role of SQDG for PSII complex in more detail, we compared structural properties and heat-tolerance of PSII between hf-2 and the wild type. Sensitivity of PSII activity to herbicides such as DCMU and CMU was higher in hf-2 than in the wild type, whereas that to atrazine was similar for both strains. Moreover, PSII complex became more fragile to be decomposed in hf-2 than in the wild-type, upon exposure to a high concentration of dodecyl b-D-maltoside. These results suggested that PSII complex with depletion of SQDG undergoes a conformational change at least around a limited region of the QB-binding site and also at sites responsible for subunit assembly of the complex. On the other hand, exposure of the cells to high temperatures in the dark lowered PSII activity more remarkably in hf-2 than in the wild type, which suggested that the PSII activity in the absence of SQDG becomes less stable under heat-stress conditions. PSII inactivated to 60% of the initial level by dark incubation at 41¡C was reactivated by following illumination even at 41¡C to more than 90% in the wild type, but only to 70% in hf-2. These results suggested that some mechanism dependent on light recovers PSII from heat-inactivation, and that SQDG is involved in functioning of the mechanism. The conformational disorder of PSII complex caused by removal of SQDG would lead to the higher susceptibility of PSII activity to heat-stress. 1. Sato et al. (1995) Eur. J. Biochem. 234, 16-23. 2. Minoda et al. (2002) Eur. J. Biochem. 269, 2353-2358.