Asymmetric structure of the native Rhodobacter sphaeroides dimeric LH1–RC complex

• Main Authors: Hall, M. (Author), Humbel, B.M (Author), Kanno, R. (Author), Kawamura, S. (Author), Kikuchi, R. (Author), Kimura, Y. (Author), Madigan, M.T (Author), Mizoguchi, A. (Author), Nagashima, K.V.P (Author), Takahashi, A. (Author), Tani, K. (Author), Wang-Otomo, Z.-Y (Author), Yu, L.-J (Author)
• Format: Article
• Language: English
• Published: Nature Research 2022
• Subjects: bacterium; membrane; peptide; protein; topology
• Online Access: View Fulltext in Publisher
• ISBN: 20411723 (ISSN)
• DOI: 10.1038/s41467-022-29453-8

Rhodobacter sphaeroides is a model organism in bacterial photosynthesis, and its light-harvesting-reaction center (LH1–RC) complex contains both dimeric and monomeric forms. Here we present cryo-EM structures of the native LH1–RC dimer and an LH1–RC monomer lacking protein-U (ΔU). The native dimer reveals several asymmetric features including the arrangement of its two monomeric components, the structural integrity of protein-U, the overall organization of LH1, and rigidities of the proteins and pigments. PufX plays a critical role in connecting the two monomers in a dimer, with one PufX interacting at its N-terminus with another PufX and an LH1 β-polypeptide in the other monomer. One protein-U was only partially resolved in the dimeric structure, signaling different degrees of disorder in the two monomers. The ΔU LH1–RC monomer was half-moon-shaped and contained 11 α- and 10 β-polypeptides, indicating a critical role for protein-U in controlling the number of αβ-subunits required for dimer assembly and stabilization. These features are discussed in relation to membrane topology and an assembly model proposed for the native dimeric complex. © 2022, The Author(s).