Study On The Structure And Function Of 33kD Manganese-Stabilizing Protein Of Photosystem Ⅱ Of Spinach

The 33 kD protein is one of the three extrinsic polypeptides of photosystem II. It is important for stabilizing Mn-cluster and reactivating O2-evolution. Recently, there are many reports about the structure of 33 kD protein and its binding to PS II. In the research, Fluorescence measurement was used to study the effect of the several solvents including CaCl2, NaCl, Urea, TCA, DTT on the solution structure of the 33 kD protein. The results suggest that the 33 kD extrinsic protein possibly has a hydrophobic core, in which the 241Trp is buried, and that most of the Tyrosine residues of the 33 kD protein are located in more hydrophobic environment. Hydrophobic interaction and disulfide are mainly responsible for maintaining the solution conformation of the MSP. CaCl2, Urea, TCA can release 33 kD protein, because they may alter the C-terminus conformation of the 33 kD protein. NaCl affected a little on the structure. So NaCl could not release 33 kD protein. D1T destroying S-S would make a big change of the structure of 33 kD protein, indicating that S-S is important to maintain the structure of 33 kD protein. Further CD measurement also confirmed the above views. In order to study the hydrophobic core Trp is buried. NBS modifying the Trp particularly was used. Then SDS-PAGE, fluorescence measurement, CD measurement and proteolysis were used to invenstage the structure alteration of modified protein. SDS-PAGE showed a increased apparent molecular mass of 34.5. Fluorescence measurement, far-UV CD and near-UV CD also indicated an apparent change. Moreover, the sites and sensitivity of hydrolyzing also changed. All results also show modifying destroyed the hydrophobic core of 33 kD protein C-terminus, which makes the solution structure of the 33 kD protein change. This indicates that the hydrophobic core in 33 kD protein C-terminus (CD research showed the hydrophobic core formed from β-sheet) is important for 33 kD proteinrebinding to PS Ⅱ particles, but it is impossible for hydrophobic core to directly involve in binding to PS n . Moreover, DSC measurement showed that 33 kD proteins has several domains and can be a "molten globular".