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Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting
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Assembly and function of the photosystem II manganese stabilizing protein: lessons from its natively unfolded

Aaron J Wyman1, Charles F Yocum

  • 1Department of Molecular, Cellular, and Developmental Biology, The University of Michigan-Ann Arbor, MI 48109, USA.

Photosynthesis Research
|July 29, 2005
PubMed

Insights

Photosystem II manganese stabilizing protein (MSP) resists heat-induced aggregation near its isoelectric point. This pH-dependent stability is crucial for forming functional protein complexes in oxygen evolution.

Area of Science:

  • Biochemistry
  • Plant Physiology
  • Protein Science

Background:

  • Photosystem II (PS II) manganese stabilizing protein (MSP) exhibits characteristics of natively unfolded proteins, including thermostability.
  • A mutant MSP (C28A, C51A) lacking the disulfide bridge retains PS II binding and oxygen evolution activity, despite increased disorder.

Purpose of the Study:

  • To investigate the effects of pH and protein concentration on the heat-induced aggregation of wild-type (WT) and mutant MSP.
  • To compare the aggregation resistance of MSP with model water-soluble proteins like bovine serum albumin (BSA) and carbonic anhydrase.

Main Methods:

  • Heat-induced aggregation assays were performed on WT and mutant MSP.
  • The influence of varying pH and protein concentration on aggregation was examined.
  • Aggregation resistance was compared between MSP, BSA, and carbonic anhydrase.

Main Results:

  • Both WT and mutant MSP showed increased resistance to heat-induced aggregation at a pH near their isoelectric point (pI) of 5.2.
  • Aggregation resistance increased for MSP and BSA at pH values above their respective pIs.
  • MSP exhibited greater aggregation resistance compared to BSA and carbonic anhydrase under tested conditions.

Conclusions:

  • MSP's aggregation resistance is pH-dependent, with maximal stability near its pI.
  • This pH-dependent stability is vital for MSP to avoid unproductive self-association and facilitate functional protein-protein interactions in the oxygen-evolving complex.
  • The findings contribute to understanding the structural properties and functional roles of MSP in photosynthesis.

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