Incoherent Energy Transfer between the Baseplate and FMO Protein Explored at Ideal Geometries

Area of Science:

• Photosynthesis research
• Biophysics
• Quantum biology

Background:

• The Fenna-Matthews-Olson (FMO) protein complex plays a crucial role in light-harvesting complexes.
• Understanding energy transfer mechanisms, like Förster resonance energy transfer (FRET), is key to comprehending photosynthetic efficiency.

Purpose of the Study:

• To investigate the FRET efficiency between the FMO protein complex and the chlorosomal baseplate (CBP).
• To determine the impact of FMO-CBP relative orientation and FMO internal structure on FRET efficiency.

Main Methods:

• Development of an idealized model based on crystal structures and molecular dynamics.
• Utilized pre-computed transition dipole moments from molecular simulations.
• Performed extensive FRET calculations (approx. 1.3 billion per model) to analyze orientation effects.

Main Results:

• FRET efficiency is remarkably independent of FMO trimer orientation (distance, displacement, rotation).
• Removing individual bacteriochlorophyll (BChl) triples from FMO reduces FRET efficiency by a maximum of 8.6%.
• An FMO with only the least efficient BChl triple retains 25% of the full FMO complex's FRET efficiency.

Conclusions:

• The FMO protein complex functions as a highly robust spatial funnel for excitation energy harvesting from the CBP.
• This spatial funneling capability is largely insensitive to the precise orientation between FMO and CBP.
• FMO's role extends beyond energy funnelling to robust spatial orientation-independent excitation harvesting.