Cryo-EM structure of the Rhodospirillum rubrum RC-LH1 complex at 2.5 Å

The reaction centre light-harvesting 1 (RC-LH1) complex is the core functional component of bacterial photosynthesis. We determined the cryo-electron microscopy (cryo-EM) structure of the RC-LH1 complex from Rhodospirillum rubrum at 2.5 angstrom resolution, which reveals a unique monomeric bacteriochlorophyll with a phospholipid ligand in the gap between the RC and LH1 complexes. The LH1 complex comprises a circular array of 16 alpha beta-polypeptide subunits that completely surrounds the RC, with a preferential binding site for a quinone, designated Q(P), on the inner face of the encircling LH1 complex. Quinols, initially generated at the RC Q(B) site, are proposed to transiently occupy the Q(P) site prior to traversing the LH1 barrier and diffusing to the cytochrome bc(1) complex. Thus, the Q(P) site, which is analogous to other such sites in recent cryo-EM structures of RC-LH1 complexes, likely reflects a general mechanism for exporting quinols from the RC-LH1 complex.

Automated summary

The RC-LH1 complex is the core functional component of bacterial photosynthesis, with a unique monomeric bacteriochlorophyll and phospholipid ligand. The LH1 complex is composed of a circular array of 16 alpha beta-polypeptide subunits that completely surrounds the RC, with a preferential binding site for a quinone designated Q(P).