Research progress on the structure of photosynthetic reaction centers-mobile electron carrier supercomplexes.

In photosynthesis, transient supercomplexes formed between reaction centers (RCs) and mobile electron carriers provide the physical interfaces that enable directional electron transfer. Recent advances in cryo-electron microscopy have substantially expanded the structural available information for these short-lived assemblies in both oxygenic and anoxygenic photosynthetic systems. This review summarizes and integrates recent high-resolution structural studies of representative RCs-mobile electron carrier supercomplexes, including Photosystem I (PSI) with plastocyanin (PC), ferredoxin (Fd), and flavodoxin (Fld) in oxygenic organisms, and RC-Light-Harvesting complex 1 (LH1) with high-potential iron-sulfur protein (HiPIP) in anoxygenic photosynthetic bacteria. Across these systems, common design features of supercomplex formation emerge, including electrostatic-hydrophobic interplay, assembly symmetry, and environmental adaptability. In oxygenic systems, the PSI-PC supercomplex follows a dynamic "electrostatic guidance-hydrophobic stabilization" model, with binding affinity modulated by the redox state of PC. PSI-Fd and PSI-Fld supercomplexes rely on synergistic electrostatic, hydrophobic, and hydrogen-bonding interactions, with Fld exhibiting symmetric, high-affinity binding under iron-deficient conditions as a functional substitute for Fd. In anoxygenic bacteria, the HiPIP-RC-LH1 supercomplex is primarily stabilized by hydrophobic interactions and hydrogen bonds, featuring a conserved transmembrane electron transfer pathway. Together, these studies provide a structural framework for understanding how interface interactions and conformational variability are related to electron transfer efficiency in photosynthetic supercomplexes, and, in doing so, outline key directions for future investigation into regulatory mechanisms, environmental adaptation, and biomimetic applications.