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.
Organizational Affiliation:
Graduate School of Medicine, Mie University, Tsu, 514-8507, Japan. ktani@doc.medic.mie-u.ac.jp.
Imaging Section, Research Support Division, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1, Tancha, Onna-son, Kunigami-gun, Okinawa, 904-0495, Japan.
Faculty of Science, Ibaraki University, Mito, 310-8512, Japan.
Research Institute for Integrated Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa, 259-1293, Japan.
Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China.
Department of Agrobioscience, Graduate School of Agriculture, Kobe University, Nada, Kobe, 657-8501, Japan.
School of Biological Sciences, Department of Microbiology, Southern Illinois University, Carbondale, IL, 62901, USA.
Graduate School of Medicine, Mie University, Tsu, 514-8507, Japan.
Faculty of Science, Ibaraki University, Mito, 310-8512, Japan. wang@ml.ibaraki.ac.jp.
AB [auth v] BA [auth 5] CB [auth y] D [auth A] DA [auth 7]
AB [auth v], BA [auth 5], CB [auth y], D [auth A], DA [auth 7], EB [auth 01], F [auth D], GB [auth 03], H [auth F], IB [auth 05], J [auth I], KA [auth a], KB [auth 07], L [auth K], MA [auth d], N [auth O], OA [auth f], P [auth Q], QA [auth i], R [auth S], SA [auth k], T [auth V], UA [auth o], V [auth Y], WA [auth q], X [auth 1], YA [auth s], Z [auth 3]
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