Structural Superimposition

Abstact

Inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)Rs) are tetrameric ER Ca(2+) channels that shape intracellular Ca(2+) signaling in response to IP(3), regulating diverse physiological processes. The structural basis for subtype-specific regulation among the three subtypes (IP(3)R-1-3) remains incompletely understood due to the lack of IP(3)R-2 structures. Here, we report cryo-electron microscopy (cryo-EM) structures of human IP(3)R-2 in distinct conformations in the presence and absence of IP(3), Ca(2+), and ATP. These structures define the conformational landscape of IP(3)R-2, delineate ligand-binding interactions, and reveal shared architectural features alongside isoform-specific differences. We also resolve ligand-dependent IP(3)R-2 assemblies, identifying a conformation-dependent inter-channel interface. Live-cell imaging demonstrates that IP(3)R-2 undergoes clustering following ligand-induced Ca(2+) release, and disruption of this interface selectively abolishes clustering without impairing channel activity. Together, these findings provide a structural framework for human IP(3)R-2 and establish a mechanism linking ligand-dependent conformational changes to inter-channel interactions and post-activation cellular clustering.