The 28 kDa apoprotein of CP 26 in PS II binds copper

Area of Science:

• Plant molecular biology
• Photosynthesis research
• Biochemistry

Background:

• Photosystem II (PS II) is crucial for photosynthesis, responsible for water splitting and oxygen evolution.
• Copper is a vital cofactor in various biological processes, including electron transport in photosynthesis.
• The role and binding proteins of copper within PS II are not fully elucidated.

Purpose of the Study:

• To identify the specific protein responsible for copper binding in spinach Photosystem II particles.
• To characterize the properties of the copper-binding protein and its interaction with copper.
• To investigate the potential function of this copper-protein complex in photosynthetic processes.

Main Methods:

• Isolation of Photosystem II particles from spinach with and without added CuSO4.
• Fractionation of PS II particles using solubilization and polyethylene glycol precipitation.
• Purification and characterization of copper-binding proteins, including amino acid sequencing and EPR spectroscopy.
• Assessment of oxygen-evolving capacity in relation to copper content.

Main Results:

• Spinach PS II particles contained varying amounts of EDTA-resistant copper, influenced by isolation conditions.
• A 28 kDa protein was purified, showing a 22-fold increase in copper concentration relative to protein.
• Partial sequencing identified a fragment of this protein as CP 26; EPR suggested oxygen/nitrogen ligands for copper.
• No correlation was found between copper content and oxygen-evolving capacity.

Conclusions:

• The 28 kDa apoprotein of CP 26 in spinach binds one copper ion per molecule.
• The identified copper-binding protein in PS II is likely CP 26.
• A potential role for this copper-CP 26 complex in the xanthophyll cycle is proposed.