Structural basis for the assembly and electron transport mechanisms of the dimeric photosynthetic RC-LH1 supercomplex

Cao, P.; Bracun, L.; Yamagata, A.; Christianson, B.; Negami, T.; Zou, B.; Terada, T.; Canniffe, D. P.; Shirouzu, M.; Li, M.; Liu, L.-N.

doi:10.1101/2021.12.17.473239

bioRxiv · 10.1101/2021.12.17.473239

Structural basis for the assembly and electron transport mechanisms of the dimeric photosynthetic RC-LH1 supercomplex

Cao, P.·Bracun, L.·Yamagata, A.·Christianson, B.·Negami, T.·Zou, B.·Terada, T.·Canniffe, D. P.·Shirouzu, M.·Li, M.·Liu, L.-N.

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Abstract

The reaction center (RC) and light-harvesting complex 1 (LH1) form a RC-LH1 core supercomplex that is vital for the primary reactions of photosynthesis in purple photosynthetic bacteria. Some species possess the dimeric RC-LH1 complex with an additional polypeptide PufX, representing the largest photosynthetic complex in anoxygenic phototrophs. However, the details of the architecture and assembly mechanism of the RC-LH1 dimer are unclear. Here we report seven cryo-electron microscopy (cryo-EM) structures of RC-LH1 supercomplexes from Rhodobacter sphaeroides. Our structures reveal that two PufX polypeptides are positioned in the center of the S-shaped RC-LH1 dimer, interlocking association between the components and mediating RC-LH1 dimerization. Moreover, we identify a new transmembrane peptide, designated PufY, which is located between the RC and LH1 subunits near the LH1 opening. PufY binds a quinone molecule and prevents LH1 subunits from completely encircling the RC, creating a channel for quinone/quinol exchange. Genetic mutagenesis, cryo-EM structures, and computational simulations enable a mechanistic understanding of the assembly and electron transport pathways of the RC-LH1 dimer and elucidate the roles of individual components in ensuring the structural and functional integrity of the photosynthetic supercomplex.

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Cao, P., Bracun, L., Yamagata, A., Christianson, B., Negami, T., Zou, B., Terada, T., Canniffe, D. P., Shirouzu, M., Li, M., Liu, L.-N.. 2021-12-18. Structural basis for the assembly and electron transport mechanisms of the dimeric photosynthetic RC-LH1 supercomplex. https://doi.org/10.1101/2021.12.17.473239

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