Role of Small Membrane Proteins in the Green Sulfur Bacterial Reaction Center

The highly efficient light-driven energy conversion in large biological complexes, such as the Photosynthetic Reaction Center (RC) of green sulfur bacteria (GSB), relies on precisely tuned protein dynamics and intersubunit communication. Small membrane proteins are critical regulators of this efficiency; yet, their mechanistic roles in dictating photophysical and electron transfer properties remain largely elusive. We leverage atomistic molecular dynamics (MD) simulations integrated with advanced Graph Network Analysis tools to uncover the functional significance of two peripheral subunits, PscE and PscF, on the GSB RC complex. These subunits occupy critical interfacial positions that dynamically regulate the complex's architecture. PscE forms a persistent interaction with PscC, exerting a steric influence on a PscA core helix. In parallel, the peripheral PscE-PscF pair modulates the coupling between PscC and the P₈₄₀ special pair, suggesting a dynamic mechanism for fine-tuning electron transfer efficiency. Our findings are consistent with cryogenic electron microscopy (Cryo-EM) electron densities and establish small auxiliary subunits as integral mechanical components that control long-range allosteric communication, providing atomic-level insight into optimizing energy conversion in natural photosystems.