Download MendeleyStructural insights into the unusual core photocomplex from a triply extremophilic purple bacterium, Halorhodospira halochloris.
Qi, C.H., Wang, G.L., Wang, F.F., Wang, J., Wang, X.P., Zou, M.J., Ma, F., Madigan, M.T., Kimura, Y., Wang-Otomo, Z.Y., Yu, L.J.(2024) J Integr Plant Biol
- PubMed: 38411333
- DOI: https://doi.org/10.1111/jipb.13628
- Primary Citation of Related Structures:
8K5O - PubMed Abstract:
Halorhodospira (Hlr.) halochloris is a triply extremophilic phototrophic purple sulfur bacterium, as it is thermophilic, alkaliphilic, and extremely halophilic. The light-harvesting-reaction center (LH1-RC) core complex of this bacterium displays an LH1-Q y transition at 1,016 nm, which is the lowest-energy wavelength absorption among all known phototrophs. Here we report the cryo-EM structure of the LH1-RC at 2.42 Å resolution. The LH1 complex forms a tricyclic ring structure composed of 16 αβγ-polypeptides and one αβ-heterodimer around the RC. From the cryo-EM density map, two previously unrecognized integral membrane proteins, referred to as protein G and protein Q, were identified. Both of these proteins are single transmembrane-spanning helices located between the LH1 ring and the RC L-subunit and are absent from the LH1-RC complexes of all other purple bacteria of which the structures have been determined so far. Besides bacteriochlorophyll b molecules (B1020) located on the periplasmic side of the Hlr. halochloris membrane, there are also two arrays of bacteriochlorophyll b molecules (B800 and B820) located on the cytoplasmic side. Only a single copy of a carotenoid (lycopene) was resolved in the Hlr. halochloris LH1-α3β3 and this was positioned within the complex. The potential quinone channel should be the space between the LH1-α3β3 that accommodates the single lycopene but does not contain a γ-polypeptide, B800 and B820. Our results provide a structural explanation for the unusual Q y red shift and carotenoid absorption in the Hlr. halochloris spectrum and reveal new insights into photosynthetic mechanisms employed by a species that thrives under the harshest conditions of any phototrophic microorganism known.
Organizational Affiliation:
Key Laboratory of Photobiology, Photosynthesis Research Center, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China.
