4.5 Article

Cryo-EM structure of the dimeric Rhodobacter sphaeroides RC-LH1 core complex at 2.9 A: the structural basis for dimerisation

Journal

BIOCHEMICAL JOURNAL
Volume 478, Issue 21, Pages 3923-3937

Publisher

PORTLAND PRESS LTD
DOI: 10.1042/BCJ20210696

Keywords

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Funding

  1. Biotechnology and Biological Sciences Research Council (BBSRC) UK [BB/M000265/1]
  2. European Research Council (ERC) [854126]
  3. Wellcome Trust [209407/Z/17/Z]
  4. Royal Society University Research Fellowship [URF\R1\191548]
  5. Royal Society

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The dimeric reaction centre light-harvesting 1 (RC-LH1) core complex of Rhodobacter sphaeroides converts absorbed light energy to a charge separation, and then it reduces a quinone electron and proton acceptor to a quinol. The interaction between the two monomers influences the curvature of the membrane vesicles where photosynthetic reactions occur. The dimerisation interface of two RC-LH1 monomers is crucial for quinones to enter and leave the complex, and for energy migration across the dimer interface.
The dimeric reaction centre light-harvesting 1 (RC-LH1) core complex of Rhodobacter sphaeroides converts absorbed light energy to a charge separation, and then it reduces a quinone electron and proton acceptor to a quinol. The angle between the two monomers imposes a bent configuration on the dimer complex, which exerts a major influence on the curvature of the membrane vesicles, known as chromatophores, where the light driven photosynthetic reactions take place. To investigate the dimerisation interface between two RC-LH1 monomers, we determined the cryogenic electron microscopy structure of the dimeric complex at 2.9 A resolution. The structure shows that each monomer consists of a central RC partly enclosed by a 14-subunit LH1 ring held in an open state by PufX and protein-Y polypeptides, thus enabling quinones to enter and leave the complex. Two monomers are brought together through N-terminal interactions between PufX polypeptides on the cytoplasmic side of the complex, augmented by two novel transmembrane polypeptides, designated protein-Z, that bind to the outer faces of the two central LH1 beta polypeptides. The precise fit at the dimer interface, enabled by PufX and protein-Z, by C-terminal interactions between opposing LH1 alpha beta subunits, and by a series of interactions with a bound sulfoquinovosyl diacylglycerol lipid, bring together each monomer creating an S-shaped array of 28 bacteriochlorophylls. The seamless join between the two sets of LH1 bacteriochlorophylls provides a path for excitation energy absorbed by one half of the complex to migrate across the dimer interface to the other half.

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