pH-induced conformational changes in the soluble manganese-stabilizing protein of photosystem II.
In this paper, we analyzed the pH-induced changes in the conformational states of the manganese-stabilizing protein (MSP) of photosystem II. Distinct conformational states of MSP were identified using fluorescence spectra, far-UV circular dichroism, and pressure-induced unfolding at varying suspension pH values, and four different conformational states of MSP were clearly distinguished using the center of fluorescence spectra mass when suspension pH was altered from 2 to 12. MSP was completely unfolded at a suspension pH above 11 and partly unfolded below a pH of 3. Analysis of the center of fluorescence spectral mass showed that the 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. Studies of peak positions of tryptophan fluorescence and MSP-bound 1-anilinonaphthalene-8-sulfonic acid fluorescence spectra supported this observation. A decrease in the suspension pH to 2 resulted in significant alterations in the MSP structure possibly because of protonation of unprotonated residues at lower pH, suggesting the existence of a large number of unprotonated amino acid residues at neutral pH possibly useful for proton transport in oxygen evolution. The acidic pH-induced conformational changes of MSP were reversible upon increase of pH to neutral pH; however, N-bromosuccinimide modification of tryptophan (Trp241) blocks the recovery of pH-induced conformational changes in MSP, implying that Trp241 is a key residue for the unfolded protein to form a functional structure. Thus, pH-induced structural changes of stable MSP (pH 6-4) may be utilized to analyze its functionality as a cofactor for oxygen evolution.
Weng
Jun
J
Institute of Plant Physiology, Shanghai Institutes for Biological Science, Chinese Academy of Sciences, Shanghai 200032, China.
Tan
Cuiyan
C
Shen
Jian-Ren
JR
Yu
Yong
Y
Zeng
Xiaomei
X
Xu
Chunhe
C
Ruan
Kangcheng
K
D001974:Bromosuccinimide / Q000737:chemistry; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008345:Manganese / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D011312:Pressure; D011487:Protein Conformation; D017510:Protein Folding; D012995:Solubility; D012996:Solutions; D013050:Spectrometry, Fluorescence; D018724:Spinacia oleracea; D014364:Tryptophan / Q000737:chemistry; D014867:Water / Q000737:chemistry
D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D012996:Solutions; C054266:photosystem II manganese-stabilizing protein; D014867:Water; D008345:Manganese; D014364:Tryptophan; D001974:Bromosuccinimide