3.E.4. The Green Sulfur Bacterial Photosynthetic Reaction Center Apparatus (GSB-PRC) Family
The cryo-EM structure of the whole photosynthetic reaction center (RC) apparatus from the green sulfur bacterium Chlorobaculum tepidum has been solved at 2.5 Å resolutiion (Xie et al. 2023). In green sulfur bacteria, light is absorbed primarily by the chlorosomes, and its energy is transferred via the Fenna- Matthews-Olson (FMO) proteins to a homodimeric reaction center (RC). Xie et al. 2023 reported the cryoEM structure of the intact FMO-RC apparatus from C. tepidum. The FMO-RC apparatus presents an asymmetric architecture and contains two FMO trimers that show different interaction patterns with the RC core. The two permanently bound transmembrane subunits PscC, which donate electrons to the special pair, interact only with the two large PscA subunits. This structure, with 7 dissimilar subunits, reveals the transfer of energy from antenna to the electron transport chain of this RC and the transfer of electrons from reduced sulfur compounds to the special pair (Xie et al. 2023).