Figure 3. 3D structure of tetrameric IP₃R1 channel determined by single-particle Cryo-EM.

Surface representation of cryo-EM density map of IP₃R1 determined by single-particle cryo-EM at intermediate resolution (EMD-5278) [9,10]. IP₃R1 protein has been visualized under conditions that favor the closed state of the channel, i.e. in the absence of its primary ligands, IP₃ and Ca²⁺ [9]. Surface representation of the structure is shown in three orthogonal views: from the cytoplasmic side (A), from the luminal side (B) and along membrane plane (C, D). One putative subunit is depicted in color; (D) two opposing subunits are shown to allow visualization of internal features in the channel structure. Scale bar is 100 Å.