Asymmetric Structure of the Native Rhodobacter sphaeroides Dimeric LH1-RC Complex

Tani, K.; Kanno, R.; Kikuchi, R.; Kawamura, S.; Nagashima, K. V. P.; Hall, M.; Takahashi, A.; Yu, L.-J.; Kimura, Y.; Madigan, M. T.; Mizoguchi, A.; Humbel, B. M.; Wang-Otomo, Z.- Y.

doi:10.1101/2021.12.14.472695

bioRxiv · 10.1101/2021.12.14.472695

Asymmetric Structure of the Native Rhodobacter sphaeroides Dimeric LH1-RC Complex

Tani, K.·Kanno, R.·Kikuchi, R.·Kawamura, S.·Nagashima, K. V. P.·Hall, M.·Takahashi, A.·Yu, L.-J.·Kimura, Y.·Madigan, M. T.·Mizoguchi, A.·Humbel, B. M.·Wang-Otomo, Z.- Y.

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Abstract

The light-harvesting-reaction center (LH1-RC) core complex of purple photosynthetic bacterium Rhodobacter (Rba.) sphaeroides is characterized by the presence of both a dimeric form and a monomeric form. Following structure determination of the monomeric LH1-RC including its previously unrecognized component designated protein-U (Nat. Commun. 12, 6300, 2021), here we present cryo-EM structures of the dimeric LH1-RC from native Rba. sphaeroides IL106 at 2.75 [A] resolution and from an LH1-RC monomer lacking protein-U ({Delta}U) at 2.64 [A] resolution. The native dimeric core complex reveals many asymmetric features in the arrangement of its two monomeric components including the structural integrity of protein-U, the overall LH1 organization, and the rigidities of the proteins and pigments that form the complex. PufX polypeptides play a critical role in connecting two monomers, with one PufX interacting at its N-terminus with another PufX and an LH1 {beta}-polypeptide in another monomer, in good agreement with biochemical analyses. One of the proteins-U was only partially identified in the dimeric structure, signaling significantly different degrees of disorder in the two monomers. The {Delta}U LH1-RC monomer revealed a half-moon-shaped structure containing 11 - and 10 {beta}-polypeptides (compared with 14 of each in the wild type), indicating a critical role for protein-U in controlling the number of {beta}-subunits required for correct assembly and stabilization of the LH1-RC dimer. The structural features are discussed in relation to the unusual topology of intracytoplasmic photosynthetic membranes and an assembly model proposed for the native Rba. sphaeroides dimeric LH1-RC complex in membranes of wild-type cells.

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Tani, K., Kanno, R., Kikuchi, R., Kawamura, S., Nagashima, K. V. P., Hall, M., Takahashi, A., Yu, L.-J., Kimura, Y., Madigan, M. T., Mizoguchi, A., Humbel, B. M., Wang-Otomo, Z.- Y.. 2021-12-15. Asymmetric Structure of the Native Rhodobacter sphaeroides Dimeric LH1-RC Complex. https://doi.org/10.1101/2021.12.14.472695

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