Bracun Laura, Yamagata Atsushi, Christianson Bern M, Shirouzu Mikako, Liu Lu-Ning
Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK; Laboratory for Protein Functional and Structural Biology, RIKEN Center for Biosystems Dynamics Research, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
Laboratory for Protein Functional and Structural Biology, RIKEN Center for Biosystems Dynamics Research, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
Structure. 2023 Mar 2;31(3):318-328.e3. doi: 10.1016/j.str.2023.01.006. Epub 2023 Feb 3.
In purple photosynthetic bacteria, the photochemical reaction center (RC) and light-harvesting complex 1 (LH1) assemble to form monomeric or dimeric RC-LH1 membrane complexes, essential for bacterial photosynthesis. Here, we report a 2.59-Å resolution cryoelectron microscopy (cryo-EM) structure of the RC-LH1 supercomplex from Rhodobacter capsulatus. We show that Rba. capsulatus RC-LH1 complexes are exclusively monomers in which the RC is surrounded by a 15-subunit LH1 ring. Incorporation of a transmembrane polypeptide PufX leads to a large opening within the LH1 ring. Each LH1 subunit associates two carotenoids and two bacteriochlorophylls, which is similar to Rba. sphaeroides RC-LH1 but more than one carotenoid per LH1 in Rba. veldkampii RC-LH1 monomer. Collectively, the unique Rba. capsulatus RC-LH1-PufX represents an intermediate structure between Rba. sphaeroides and Rba. veldkampii RC-LH1-PufX. Comparison of PufX from the three Rhodobacter species indicates the important residues involved in dimerization of RC-LH1.
在紫色光合细菌中，光化学反应中心（RC）和光捕获复合体1（LH1）组装形成单体或二聚体RC-LH1膜复合体，这对细菌光合作用至关重要。在此，我们报道了来自荚膜红细菌的RC-LH1超复合体的分辨率为2.59埃的冷冻电子显微镜（cryo-EM）结构。我们发现，荚膜红细菌的RC-LH1复合体均为单体，其中RC被一个由15个亚基组成的LH1环包围。跨膜多肽PufX的掺入导致LH1环内出现一个大的开口。每个LH1亚基结合两个类胡萝卜素和两个细菌叶绿素，这与球形红细菌的RC-LH1相似，但在费氏红细菌的RC-LH1单体中每个LH1的类胡萝卜素不止一个。总体而言，独特的荚膜红细菌RC-LH1-PufX代表了球形红细菌和费氏红细菌RC-LH1-PufX之间的中间结构。对三种红细菌属物种的PufX进行比较，表明了参与RC-LH1二聚化的重要残基。
