Double concentric ring organization of light harvesting complexes in Gemmatimonas phototrophica
Doc. Michal Koblížek Ph.D.
Michal Koblížek, Alastair Gardiner, Nupur, Tomáš Polívka, Niel Hunter and Pu Qian
Anoxygenic photosynthesis has previously been described in the bacterial phyla; Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, Firmicutes and Acidobacteria. Recently we described a phototrophic bacterium belonging to phylum Gemmatimonadetes . This organisms Gemmatimonas phototrophica evolved the ability to use solar energy following horizontal transfer of photosynthesis-related genes from an ancient phototrophic proteobacterium. Our previous study indicated that it contains a unique arrangement of light-harvesting (LH) complexes . Thus, we used the cryo-EM technique to investigate its detailed structure. The complex contains the type-2 reaction center surrounded by two concentric rings of light harvesting antennae. The outer LH ring consist of 24 subunits and contains 72 bacteriochlorophyll (BChl) molecules. The inner ring consists of 16 subunits, with 32 BChls. The function of the light harvesting complexes was investigated using fs-spectroscopy. It was found that the LH rings serve as an energy funnel with the pigments at higher excitation energy placed at the periphery and the pigments with lower energy in the centre. The excitation energy migrates within picoseconds down the energy gradient and is finally trapped in the RC. References: 1. Zeng, Y, Feng, F, Medová, H, Dean, J, Koblížek, M: Functional type 2 photosynthetic Reaction centers found in the rare bacterial phylum Gemmatimonadetes. Proc. Natl. Acad. Sci. USA 111: 7795-800, 2014. 2. Dachev, M, Bína, D, Sobotka, R, Moravcová, L, Gardian, Z, Kaftan, D, Šlouf, V, Fuciman, M, Polívka, T, Koblížek, M: Unique double concentric ring organization of light harvesting complexes in Gemmatimonas phototrophica. Plos Biology 15, e2003943, 2017.
Link to the online seminar: https://cuni-cz.zoom.us/j/96375319746