pH-Dependent Conformational Switch Impacts Stability of the PsbS Dimer.

Area of Science:

• Plant molecular biology
• Photosynthesis research
• Photoprotection mechanisms

Background:

• The photosystem II PsbS protein is crucial for plant photoprotection.
• PsbS senses thylakoid lumen acidification to trigger photoprotective responses.
• The pH-dependent monomerization of PsbS is proposed but lacks direct evidence linking structural changes to dimer stability.

Purpose of the Study:

• To investigate the pH-dependent structural response of the PsbS dimer.
• To elucidate the connection between pH-induced structural changes and PsbS dimer stability.
• To understand how PsbS conformation influences dimerization and the photoprotective mechanism.

Main Methods:

• Constant pH coarse-grained molecular dynamics simulations.
• All-atom molecular dynamics simulations.
• Analysis of structural changes in PsbS dimer interfaces.

Main Results:

• pH variations induce structural changes in lumen-exposed helices at the PsbS dimeric interface.
• These structural changes act as a switch between inactive and active PsbS forms.
• Monomerization free energy calculations show weaker protein-protein interactions at neutral pH due to disrupted H-bond networks.

Conclusions:

• The study reveals how pH-dependent conformations of PsbS directly impact its dimerization propensity.
• This pH-mediated dimerization is fundamental to the plant photoprotective mechanism.
• The findings provide a structural basis for understanding PsbS function in photosynthesis.