Cryo-EM structure of the Rhodobaca bogoriensis RC-LH1-PufX dimeric complex at 2.9 Å

The reaction centre-light harvesting 1 (RC-LH1) complex is essential for converting light into proton motive force in photosynthetic bacteria. RC-LH1 is a monomer in most purple bacteria, but in Rhodobacter species, it is a dimer. Its assembly depends on an accessory polypeptide (PufX) and, ultimately, on photosynthetic growth. To date, knowledge on the RC-LH1-PufX structure, where the dimer has two incomplete ‘C’-shaped antenna rings surrounding an RC, is mainly limited to the model organism Rhodobacter sphaeroides . Here we present a cryo-electron microscopy structure at 2.9 Å from Rhodobaca bogorensis strain LBB1. RCs are surrounded by 30 antennas and incorporate protein Y and PufX. RCs are stably connected by PufX, which self-interacts, electrostatically attracts cytochrome c2 (cyt c2 ) and forms extensive networks with co-factors. This structure underlines coordinated energy transfer in a combinatorial manner, providing a basis to describe bacterial photosynthesis within a dimeric photosynthetic apparatus.