Water Networks in Photosystem II Using Crystalline Molecular Dynamics Simulations and Room-Temperature XFEL Serial...

Area of Science:

• Biophysics
• Structural Biology
• Photosynthesis Research

Background:

• Water and hydrogen bonds are vital for enzyme function, particularly in proton, ion, and substrate transport.
• Understanding these dynamics in Photosystem II (PS II) is key to elucidating the water oxidation reaction mechanism.

Purpose of the Study:

• To investigate the structural dynamics of water and hydrogen-bonding networks in the dark-stable S1 state of PS II.
• To compare atomistic molecular dynamics (MD) simulations with experimental data from serial femtosecond X-ray crystallography.

Main Methods:

• Performed large-scale crystalline molecular dynamics (MD) simulations of a full unit cell of PS II in explicit solvent.
• Computed simulated crystalline electron density to compare with experimental X-ray crystallography data.
• Developed and applied a novel Map-based Acceptor-Donor Identification (MADI) technique to analyze hydrogen-bond networks.

Main Results:

• MD simulations accurately reproduced experimental electron density and water positions.
• Simulations revealed dynamic water exchange and transport through PS II channels, offering insights beyond experimental B-factors.
• MADI analysis identified hydrogen-bond wires from the Mn cluster through Cl1 and O4 channels, suggesting proton transfer pathways.

Conclusions:

• Atomistic simulations provide unprecedented detail on water dynamics and hydrogen-bonding networks in PS II.
• The identified hydrogen-bond wires may facilitate proton transfer essential for the water oxidation cycle.
• These findings enhance our understanding of PS II function and the water oxidation reaction.