Journal
STRUCTURE
Volume 31, Issue 3, Pages 318-+Publisher
CELL PRESS
DOI: 10.1016/j.str.2023.01.006
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In this study, the structure of RC-LH1 supercomplex from purple photosynthetic bacteria Rhodobacter capsulatus is reported using cryo-EM. The RC-LH1 complexes in Rba. capsulatus are exclusively monomers surrounded by a LH1 ring. Insertion of transmembrane polypeptide PufX leads to a large opening within the LH1 ring. Comparison of PufX from different Rhodobacter species reveals the important residues involved in RC-LH1 dimerization.
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 photo-synthesis. Here, we report a 2.59-A resolution cryoelectron microscopy (cryo-EM) structure of the RC-LH1 supercomplex from Rhodobacter capsulatus. We show that Rba. capsulatus RC-LH1 complexes are exclu-sively 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.
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