Acetonitrile-induced unfolding of the photosystem II manganese-stabilizing protein studied by electrospray mass spectrometry.
In this paper an acetonitrile-induced unfolding of the manganese-stabilizing protein (MSP) of photosystem II was discovered. More distinct unfolding states of MSP were identified than previously by using mainly electrospray ionization mass spectrometry (ESI-MS), together with fluorescence spectra and far-UV circular dichroism (CD) at pH 2.0, 6.2 or 11.6, and with acetonitrile concentrations from 0 to 50%. At pH 6.2 with acetonitrile concentration changing from 0 to 10%, relatively broad charge-state distributions and poor intensity were observed in ESI-MS, indicating the presence of coexisting conformers. It was concluded that the structure of the MSP protein is unlikely to be a tightly folded form. When the concentration of acetonitrile was 20-40%, simulating the state in the biological membrane, changes in the state of unfolding of MSP were observed to a certain extent using ESI-MS, fluorescence and CD spectroscopy. The charge-state distribution in ESI-MS was found to move toward high states (from 13+ to 27+ to 15+ to 31+) with increasing acetonitrile concentration. At pH 2.0, the MSP structure is rearranged into an unfolded state, and at pH 11.6 the MSP structure is induced to assume another unordered state by deprotonation of appropriate residues. An interesting observation was that a second peak envelope emerged with 20-50% acetonitrile in the medium at pH 11.6.
Zhang
Li
L
Shanghai Mass Spectrometry Center, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China.
Zhang
Feng
F
Zhang
Su-Yan
SY
Guo
Yin-Long
YL
Xu
Chun-He
CH
D000097:Acetonitriles / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D017510:Protein Folding; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D018724:Spinacia oleracea / Q000737:chemistry
D000097:Acetonitriles; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C054266:photosystem II manganese-stabilizing protein; D008345:Manganese; C032159:acetonitrile