Macroscale optimal size of ICM vesicles regulated by quantum design principle in LH2 structure.

The photosynthetic bacterial light-harvesting antenna complex 2 (LH2), consisting of ring-like bacteriochlorophylls aggregates, constitutes an optimal excitonic structure for efficient energy transfer. Any distortion from this structure would cause efficiency losses. When adapted to low-light growing conditions, LH2-embedded membranes form vesicles to enhance light capture, albeit at the expense of curvature-induced LH2 deformation. Therefore, evolution should optimize vesicle sizes for overall light utilization efficiency. To unveil this optimization strategy, LH2 was assembled onto silica nanoparticles of a wide size region to simulate LH2 deformation, which was characterized by the B850 lifetime both theoretically and experimentally. We found that LH2 was undeformed only within the size range of 50-80 nm, akin to vesicle sizes observed in bacteria, suggesting that vesicle size optimization follows the LH2 structural design principle.