PARENT SESSION
Posters P7A Mechanisms of water oxidation. Abstracts (347-381)

Study on the relationship between structure of photosynthetic oxygenic extrinsic proteins and their physiological functions. Jun Weng¹, Chunhe Xu^*,1, Kangcheng Ruan², ¹ Institute of Plant Physiology, Shanghai Institutes for Biological Science, Chinese Academy of Sciences (CAS), Shanghai, China² Labotatory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Science, CAS, Shanghai, China

ABSTRACT- Among the proteins that function in PS II oxygen evolution, three extrinsic proteins, 33, 23 and 17 kDa proteins, play important roles in oxygen evolution under physiological conditions and show special structure characters. 33 kDa protein is also called manganese stabilizing protein (MSP). pH-induced changes in the conformational states of MSP was studied. Four conformational states of MSP were identified using fluorescence, far-UV CD, and pressure-induced unfolding at varying suspension pH values. MSP is completely unfolded at a suspension pH above 11, and partly unfolded below a pH of 3. MSP structure appears stably folded around pH 6 and 4. The conformational state of MSP at pH 4 seems more stable than that at pH 6. A decrease in the suspension pH to 2 resulted in significant alterations in the structure of MSP, suggesting the presence of a large number of unprotonated amino acid residues possibly used for proton transport in oxygen evolution. NBS modification of Trp241 blocks the recovery of low pH-induced conformational changes in MSP, implying that Trp241 is a key residue for the unfolded protein to form a functional structure. pH-induced structural changes of stable MSP (pH 6 to 4) might be utilized to analyze its function as a cofactor for oxygen evolution. It is known that MSP is easy to be unfolded under pressure. The thermodynamic analysis of stabilization on MSP by sucrose and glycerol against pressure-induced unfolding showed that the rate of pressure-induced unfolding in the presence of sucrose or glycerol was slower than the refolding rate although both were significantly slower than that observed without any stabilizers. Pressure-induced unfolding of 23 and 17 kDa protein has also been studied respectively. It was showed that both 23 and 17 kDa protein are easy to be unfolded under pressure.

KEY WORDS: manganese stabilizing protein, oxygen evolution, extrinsic proteins