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Structure of the light harvesting 2 complex reveals two carotenoid energy transfer pathways in a photosynthetic bacterium

Gardiner, A. T.; Naydenova, K.; Hartmann, P. C.; Nguyen-Phan, T. C.; Russo, C. J.; Sader, K.; Hunter, C. N.; Cogdell, R. J.; Qian, P.

2020-10-21 biochemistry
10.1101/2020.10.21.349431 bioRxiv
Show abstract

We report the 2.4 [A] resolution structure of the light harvesting 2 complex (LH2) from Marichromatium (Mch.) purpuratum determined by electron cryo-microscopy. The structure contains a heptameric ring that is unique among all known LH2 structures, explaining the unusual spectroscopic properties of this bacterial antenna complex. Two sets of distinct carotenoids are identified in the structure, and a network of energy transfer pathways from the carotenoids to bacteriochlorophyll a molecules is shown. The geometry imposed by the heptameric ring controls the resonant coupling of the long wavelength energy absorption band. Together, these details reveal key aspects of the assembly and oligomeric form of purple bacterial LH2 complexes that were previously inaccessible by any technique. One Sentence SummaryThe structure of a heptameric LH2 antenna complex reveals new energy transfer pathways and the basis for assembling LH rings.

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