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bioRxiv · 10.1101/2021.05.30.446358

Cryo-EM Structure of the Photosynthetic LH1-RC Complex from Rhodospirillum rubrum

Tani, K.·Kanno, R.·Ji, X.- C.·Hall, M.·Yu, L.- J.·Kimura, Y.·Madigan, M. T.·Mizoguchi, A.·Humbel, B. M.·Wang-Otomo, Z.- Y.
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Abstract

We present a cryo-EM structure of the light-harvesting-reaction center (LH1-RC) core complex from purple phototrophic bacterium Rhodospirillum (Rsp.) rubrum at 2.76 [A] resolution. The LH1 complex forms a closed, slightly elliptical ring structure with 16 {beta}-polypeptides surrounding the RC. Our biochemical analysis detected rhodoquinone (RQ) molecules in the purified LH1-RC, and the cryo-EM density map specifically positions RQ at the QA site in the RC. The geranylgeraniol sidechains of bacteriochlorophyll (BChl) aG coordinated by LH1 {beta}-polypeptides exhibit a highly homologous tail-up conformation that allows for interactions with the bacteriochlorin rings of nearby LH1 -associated BChls aG. The structure also revealed key protein-protein interactions in both N- and C-terminal regions of the LH1 {beta}-polypeptides, mainly within a face-to-face structural subunit. Our findings enable to evaluate past experimental and computational results obtained with this widely used organism and provide crucial information for more detailed exploration of light-energy conversion, quinone transport, and structure-function relationships in pigment-protein complexes.

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Tani, K., Kanno, R., Ji, X.- C., Hall, M., Yu, L.- J., Kimura, Y., Madigan, M. T., Mizoguchi, A., Humbel, B. M., Wang-Otomo, Z.- Y.. 2021-05-31. Cryo-EM Structure of the Photosynthetic LH1-RC Complex from Rhodospirillum rubrum. https://doi.org/10.1101/2021.05.30.446358

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