Excitation energy equilibration in a trimeric LHCII complex involves unusual pathways

Area of Science:

• Photosynthesis research
• Biophysics
• Quantum biology

Background:

• Light-harvesting complex II (LHCII) trimers are crucial for light capture in photosynthesis.
• Understanding energy equilibration dynamics within LHCII is key to comprehending photosynthetic efficiency.

Purpose of the Study:

• To investigate the mechanisms of energy equilibration within the LHCII trimer.
• To elucidate the role of chlorophyll a and b in energy transfer pathways.

Main Methods:

• Utilized Redfield-Förster method with varying compartmentalization.
• Employed the exact hierarchical equation of motion (HEOM) for precise calculations.

Main Results:

• Identified inter-monomeric energy migration beyond direct chlorophyll a transfers.
• Discovered uphill transfers from chlorophyll a to stromal-side chlorophyll b, increasing transfer rates by 1.5x.
• Observed depopulation of the long-lived Chl a604 state via stromal-side Chl b.
• Demonstrated accelerated intra- and inter-monomeric transfers from Chl a604 due to Chl b interactions.

Conclusions:

• Energy equilibration in LHCII trimers is facilitated by complex pathways involving chlorophyll b.
• Uphill energy transfers and chlorophyll b-mediated depopulation significantly enhance photosynthetic energy transfer efficiency.