Protein-independent light harvesting governed by structural heterogeneity
Arai, S.; Inagaki, T.; Harada, J.; Azai, C.; Kondo, T.
Show abstract
Chlorosomes are the largest known photosynthetic light-harvesting antennas, yet unlike protein-based antennas, they lack protein scaffolds that organize pigment molecules and instead contain self-assembled tubular and lamellar bacteriochlorophyll aggregates. How these antennas achieve directional and efficient energy transfer has remained unresolved. By applying ultrafast transient absorption spectroscopy to individual wild-type and mutant chlorosomes, we resolved six kinetic components obscured by ensemble averaging and assigned each to either lamellar or tubular aggregates. Lamellar aggregates expand light-harvesting capacity, whereas tubular aggregates serve as the primary energy donors to the baseplate. Such structural heterogeneity is therefore not merely suppressed but tuned to balance light-harvesting capacity with robust energy delivery. These findings reveal a division-of-labor strategy among pigment aggregates for efficient light harvesting without protein scaffolds.
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