Structural and dynamic insights into Mn₄Ca cluster-depleted Photosystem II

Area of Science:

• Biochemistry
• Photosynthesis research
• Structural biology

Background:

• Oxygenic photosynthesis initiates with water oxidation by the Mn4Ca cluster in Photosystem II (PSII).
• Photoactivation is crucial for assembling and repairing the Mn4Ca cluster within PSII.
• Understanding apo PSII (PSII lacking the Mn4Ca cluster) is key to comprehending photoactivation and advancing artificial photosynthesis.

Purpose of the Study:

• To structurally and dynamically characterize apo PSII using molecular dynamics simulations.
• To investigate the influence of different protonation states within the cluster cavity.
• To assess the pre-organization of the active site for Mn4Ca cluster assembly.

Main Methods:

• Classical Molecular Dynamics (MD) simulations were employed.
• Simulations were performed on apo PSII models with varying protonation states.
• Structural and dynamic features of the active site were analyzed.

Main Results:

• Apo PSII exhibited overall conformational stability across different protonation states.
• Significant deviations were observed in active site side chain conformations compared to X-ray data.
• Not all manganese-binding residues appear pre-organized for initial Mn ion binding.

Conclusions:

• The active site of apo PSII is not fully pre-organized for Mn4Ca cluster formation.
• Local conformational adjustments are necessary before the first manganese ion can bind.
• These findings provide insights into the initial steps of Mn4Ca cluster assembly in PSII.