Low pH-induced conformational changes in 33 kD protein of photosystem Ⅱ  

作　　者：WENGJun TANCuiyan YUYong RUANKangcheng XUChunhe 

机构地区：[1]InstituteofPlantPhysiology,ShanghaiInstitutesforBiologicalSci-ences,ChineseAcademyofSciences,Shanghai200032,China [2]LaboratoryofProteomics,InstituteofBiochemistryandCellBiology.ShanghaiInstitutesforBiologicalSciences,ChineseAcademyofSci-ences,Shanghai200031,China

出　　处：《Chinese Science Bulletin》2004年第9期921-925,共5页

摘　　要：kD protein, located on the lumen side of thylakoid membranes, is one of three extrinsic proteins of photosystemⅡ(PSⅡ). Previous study showed that NBS modification of W241, the only tryptophan in 33 kD protein, is helpful for understanding the function of W241 in main-taining functional conformation of 33 kD protein. In this paper, studies of both circular dichroism and fluorescence spectra showed that upon decreasing pH from 6.2 to 2.5, the conformation of soluble 33 kD protein changed significantly, with an increase or a decrease in percentage of random coil or a-helix and turns. The changes in secondary structures of this protein are pH reversible. After NBS modification at pH 2.5, the conformational change of 33 kD protein was kept fixed. The CD ellipticity at 200 nm for NBS-modified 33 kD protein is much lower than that for control, indicating that the unfolding degree of 33 kD protein was enhanced after the NBS modification. Moreover, the conformational flexibility is lost in NBS-modified 33 kD protein, and the conformational change becomes pH irreversible, indicating that NBS modi-fication blocked the reversibility of conformational change of 33 kD protein. The specific binding capability of NBS-modi- fied 33 kD protein is much lower than that of low pH-treated control. Furthermore, the rebinding of modified protein on PSⅡ membranes cannot restore the activity of oxygen evo-lution. We suggest that it is low pH but not NBS modification of W241 that leads to the conformational change of 33 kD protein from one functional to another non-functional state. The significant capability of proton transport of 33 kD pro-tein is discussed.kD protein, located on the lumen side of thylakoid membranes, is one of three extrinsic proteins of photosystemⅡ(PSⅡ). Previous study showed that NBS modification of W241, the only tryptophan in 33 kD protein, is helpful for understanding the function of W241 in main-taining functional conformation of 33 kD protein. In this paper, studies of both circular dichroism and fluorescence spectra showed that upon decreasing pH from 6.2 to 2.5, the conformation of soluble 33 kD protein changed significantly, with an increase or a decrease in percentage of random coil or a-helix and turns. The changes in secondary structures of this protein are pH reversible. After NBS modification at pH 2.5, the conformational change of 33 kD protein was kept fixed. The CD ellipticity at 200 nm for NBS-modified 33 kD protein is much lower than that for control, indicating that the unfolding degree of 33 kD protein was enhanced after the NBS modification. Moreover, the conformational flexibility is lost in NBS-modified 33 kD protein, and the conformational change becomes pH irreversible, indicating that NBS modi-fication blocked the reversibility of conformational change of 33 kD protein. The specific binding capability of NBS-modi- fied 33 kD protein is much lower than that of low pH-treated control. Furthermore, the rebinding of modified protein on PSⅡ membranes cannot restore the activity of oxygen evo-lution. We suggest that it is low pH but not NBS modification of W241 that leads to the conformational change of 33 kD protein from one functional to another non-functional state. The significant capability of proton transport of 33 kD pro-tein is discussed.

关 键 词：NBS修正 33KD蛋白 色氨酸 功能性构象 类囊体 光合体系 

分 类 号：Q945.11[生物学—植物学] Q946.1