PT  - JOURNAL ARTICLE
AU  - K. Tani
AU  - R. Kanno
AU  - X.-C. Ji
AU  - M. Hall
AU  - L.-J. Yu
AU  - Y. Kimura
AU  - M. T. Madigan
AU  - A. Mizoguchi
AU  - B. M. Humbel
AU  - Z.-Y. Wang-Otomo
TI  - Cryo-EM Structure of the Photosynthetic LH1-RC Complex from <em>Rhodospirillum rubrum</em>
AID  - 10.1101/2021.05.30.446358
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.05.30.446358
4099  - http://biorxiv.org/content/early/2021/05/31/2021.05.30.446358.short
4100  - http://biorxiv.org/content/early/2021/05/31/2021.05.30.446358.full
AB  - 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 Å resolution. The LH1 complex forms a closed, slightly elliptical ring structure with 16 αβ-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 β-polypeptides exhibit a highly homologous tail-up conformation that allows for interactions with the bacteriochlorin rings of nearby LH1 α-associated BChls aG. The structure also revealed key protein–protein interactions in both N- and C-terminal regions of the LH1 αβ-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.Competing Interest StatementThe authors have declared no competing interest.