Abstract
Type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) is the predominant Ca2+-release channel in neurons. IP3R1 mediates Ca2+ 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 IP3R1 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 IP3R1 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 IP3R1 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.
Highlights
Type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) is the predominant Ca2+-release channel in neurons
Embedding IP3R1 into nanodiscs and protein purification was essentially a one-step procedure using immunoaffinity chromatography (Supplementary Fig. 1a; see “Methods” section), minimizing exposure of the solubilized channel protein to detergent and avoiding further displacement of lipid molecules while reconstituting the purified channel particles in a near-native lipid environment. Both IP3R1 reconstituted in lipid nanodiscs (IP3R1-ND) and IP3R1 solubilized in Lauryl Maltose Neopentyl Glycol (LMNG) (IP3R1-LMNG) preparations were analyzed by cryo-EM under similar conditions in the presence of EGTA and without the addition of any channel-specific ligands
In the present study, we have solved the first structure of the fulllength neuronal IP3R1 channel reconstituted in lipid nanodiscs, which provides a native-like lipid bilayer environment suitable for cryo-EM structural characterization of the membrane protein in a soluble, detergent-free form
Summary
Type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) is the predominant Ca2+-release channel in neurons. We present the cryo-EM structures of full-length rat IP3R1 reconstituted in lipid nanodisc and detergent solubilized in the presence of phosphatidylcholine determined in ligand-free, closed states by single-particle electron cryo-microscopy. Both structures exhibit the well-established IP3R1 protein fold and reveal a nearly complete representation of lipids with similar locations of ordered lipids bound to the transmembrane domains. To understand how IP3R channels convey their gating through the interplay of its two primary agonists, IP3 and Ca2+, structures of IP3Rs in both the apo- and ligand-bound states have been determined at nearatomic resolutions by single-particle electron cryo-microscopy (cryo-EM). Structural comparisons of the channels visualized in these two different milieus in a ligand-free state provide insights into IP3R1-lipid interactions enabling a deeper understanding of IP3R channel function in a physiologically relevant membrane environment
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
