Cryo-EM reveals ligand induced allostery underlying InsP(3)R channel gating

Inositol-1,4,5-trisphosphate receptors (InsP(3)Rs) are cation channels that mobilize Ca(2+) from intracellular stores in response to a wide range of cellular stimuli. The paradigm of InsP(3)R activation is the coupled interplay between binding of InsP(3) and Ca(2+) that switches the ion conduction pathway between closed and open states to enable the passage of Ca(2+) through the channel. However, the molecular mechanism of how the receptor senses and decodes ligand-binding signals into gating motion remains unknown. Here, we present the electron cryo-microscopy structure of InsP(3)R1 from rat cerebellum determined to 4.1 Å resolution in the presence of activating concentrations of Ca(2+) and adenophostin A (AdA), a structural mimetic of InsP(3) and the most potent known agonist of the channel. Comparison with the 3.9 Å-resolution structure of InsP(3)R1 in the Apo-state, also reported herein, reveals the binding arrangement of AdA in the tetrameric channel assembly and striking ligand-induced conformational rearrangements within cytoplasmic domains coupled to the dilation of a hydrophobic constriction at the gate. Together, our results provide critical insights into the mechanistic principles by which ligand-binding allosterically gates InsP(3)R channel.