Structural Studies of IP3R by Cryoem

Abstract

Inositol 1,4,5-trisphosphate receptors (IP3Rs) play important roles in a battery of cellular activities. Structural study of the receptors is therefore very important for understanding how they are gated by their natural ligands and are modulated by their intracellular partners. In the past several years, multiple groups have generated very disparate reconstructions of the type 1 IP3R. Striking structural variations have been reported for the receptors in different detergents and for the receptors prepared from native and sf9 cells by the same research groups, suggesting that biochemical preparations of the receptors might have had significant variations and that the heterogeneity in the samples could be a limiting factor in reaching accordant results. To resolve such discrepancies, we developed a three- layered strategy to enhance biochemical homogeneity and structural agreements. We collected two cryoEM datasets of the receptors in the absence and presence of IP3 and Ca2+ and calculated two separate reconstructions. The two structures not only agree with each other in many aspects, but also reveal a conformational change at the top of the cytosolic domain that may lead to some reorganization of the channel pore. In order to verify the structural details and solidify the conformational changes in the pore domain, we need higher resolution structures. We are using the high-end facilities with direct electron detectors to collect near-atomic resolution data in order to further improve the resolutions of our 3D reconstructions.