LHCSR1 Functions as a Dimmer Switch for Light Harvesting.

Area of Science:

• Photosynthesis research
• Plant photoprotection mechanisms
• Molecular spectroscopy

Background:

• Oxygenic photosynthesis requires photoprotective processes under high light.
• Light-harvesting stress-related (LHCSR) proteins are key for photoprotection in moss and algae.
• LHCSR activation involves thylakoid lumen acidification and violaxanthin to zeaxanthin conversion.

Purpose of the Study:

• To investigate the function of LHCSR1 in its native membrane environment using single-molecule fluorescence spectroscopy.
• To determine how the membrane environment, pH, and zeaxanthin affect LHCSR1's photoprotective activity.

Main Methods:

• Employed single-molecule fluorescence spectroscopy.
• Studied LHCSR1 reconstituted into membrane nanodiscs to mimic the native membrane environment.

Main Results:

• The membrane environment significantly enhanced overall photoprotection (quenching) irrespective of pH or zeaxanthin.
• pH-dependent quenching remained evident, but zeaxanthin-dependent quenching was diminished in the membrane.
• Increased conformational changes were observed in the membrane, indicating environmental influence on protein function.

Conclusions:

• The native membrane environment modulates LHCSR1 function, enhancing photoprotection.
• Local membrane environment alters the balance between light harvesting and energy dissipation.
• Zeaxanthin's role in quenching may be less dominant in the native membrane compared to detergent-solubilized states.