Conformational changes in a Photosystem II hydrogen bond network stabilize the oxygen-evolving complex.

Area of Science:

• Photosynthesis research
• Plant biochemistry
• Molecular biology

Background:

• The Mn4CaO5 oxygen-evolving complex (OEC) in Photosystem II (PSII) is crucial for water oxidation.
• The PsbO subunit stabilizes the OEC and aids proton transfer after OEC assembly.
• D1 residue R334 is involved in proton release and interacts with PsbO, showing conformational changes.

Purpose of the Study:

• Investigate the function of D1 residue R334 in PSII and OEC assembly.
• Understand the role of the D1-R334 hydrogen bond network in OEC stability and PsbO interaction.

Main Methods:

• Generated a D1-R334G point mutant in Synechocystis sp. PCC 6803.
• Assessed PSII activity and OEC stability under different light conditions.
• Analyzed isolated core complexes for PsbO binding and manganese content.
• Studied the stabilization of the S2 intermediate in the mutant.

Main Results:

• D1-R334G PSII is active in continuous light but shows OEC instability in darkness.
• Isolated D1-R334G core complexes exhibit reduced PsbO binding and lower manganese content compared to wild type.
• The S2 intermediate is stabilized in the D1-R334G mutant, indicating altered OEC environment.
• These findings suggest a different functional conformation of the D1-R334 network during OEC biogenesis prior to PsbO docking.

Conclusions:

• The D1-R334 residue and its associated hydrogen bond network play a critical role in OEC stability and proper PsbO interaction.
• The conformation of the D1-R334 network differs during OEC assembly before PsbO binding, influencing manganese incorporation and stability.