Cryo-EM structure of type 1 IP3R channel in a lipid bilayer
Mariah R. Baker, Guizhen Fan, Alexander Seryshev, Melina A. Agosto, Matthew L. Baker, Irina I. Serysheva
Abstract
Abstract Type 1 inositol 1,4,5-trisphosphate receptor (IP 3 R1) is the predominant Ca 2+ -release channel in neurons. IP 3 R1 mediates Ca 2+ release from the endoplasmic reticulum into the cytosol and thereby is involved in many physiological processes. Here, we present the cryo-EM structures of full-length rat IP 3 R1 reconstituted in lipid nanodisc and detergent solubilized in the presence of phosphatidylcholine determined in ligand-free, closed states by single-particle electron cryo-microscopy. Notably, both structures exhibit the well-established IP 3 R1 protein fold and reveal a nearly complete representation of lipids with similar locations of ordered lipids bound to the transmembrane domains. The lipid-bound structures show improved features that enabled us to unambiguously build atomic models of IP 3 R1 including two membrane associated helices that were not previously resolved in the TM region. Our findings suggest conserved locations of protein-bound lipids among homotetrameric ion channels that are critical for their structural and functional integrity despite the diversity of structural mechanisms for their gating.