Figure 1. Structure of the N-terminal of the IP₃ receptor and structures of the ligands used.

(A) Key regions of a single IP₃R subunit (numbering for rat IP₃R1) are shown highlighting N-terminal domains and the six C-terminal transmembrane domains (TMD) that form the pore. A high-resolution structure of the N-terminal (NT, residues 1–604) with (1,4,5)IP₃ bound is shown (Protein Data Bank, 3UJO). The NT comprises the suppressor domain (SD) and IP₃-binding core (IBC). The essential 4- and 5-phosphate groups of (1,4,5)IP₃ interact with residues in the β-domain and α-domain of the IBC, respectively. (B) Structures of the ligands used.