Cryo-EM structure of a monomeric RC-LH1-PufX supercomplex with high-carotenoid content from Rhodobacter capsulatus

Structure. 2023 Mar 2;31(3):318-328.e3. doi: 10.1016/j.str.2023.01.006. Epub 2023 Feb 3.

Abstract

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.

Keywords: PufX; RC-LH1 complex; Rhodobacter capsulatus; carotenoid; cryo-EM; photosynthesis; quinone transport.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carotenoids / metabolism
  • Cryoelectron Microscopy
  • Light-Harvesting Protein Complexes / chemistry
  • Light-Harvesting Protein Complexes / metabolism
  • Rhodobacter capsulatus* / metabolism
  • Rhodobacter sphaeroides* / chemistry
  • Rhodobacter sphaeroides* / metabolism

Substances

  • Light-Harvesting Protein Complexes
  • Carotenoids