Structural dynamics of adenine nucleotide potentiation of the human type 2 IP₃ receptor

Inositol trisphosphate receptors (IP₃R) are intracellular calcium (Ca²⁺) channels that mediate Ca²⁺ flux from the endoplasmic reticulum (ER) into the cytosol, playing a critical role in Ca²⁺ signaling. IP₃R activity requires IP₃ and Ca²⁺ and is potentiated by adenine nucleotides through a poorly understood mechanism. Here, we combined single-particle cryo-electron microscopy and all-atom molecular dynamics simulations to investigate the potentiation of IP₃Rs by adenine nucleotides. Our structures reveal that ATP and cAMP bind to a conserved site in the juxtamembrane domain, which connects the cytoplasmic IP₃- and Ca²⁺-binding sites with the transmembrane pore. Molecular dynamics simulations predict that the binding of adenine nucleotides rigidifies the juxtamembrane domain, primarily through the coordination of the adenine base. Consistent with the adenine base being critical for potentiation, mutations that disrupt the interactions with the adenine base perturb Ca²⁺ flux in cells. Taken together, our data suggest that adenine nucleotides potentiate IP₃R channel activity by rigidifying the juxtamembrane domain to improve coupling between IP₃ and Ca²⁺ binding and pore opening.