Endoplasmic reticulum/Sarcoplasmic reticulum receptors

The specific type of inositol 1,4,5-trisphosphate receptor (InsP₃R) protein discussed here is the mouse type 1 InsP₃R, also called InsP₃R1. This polypeptide contains three major regions: the <scene name='38/382942/N_terminal_domain/1'>amino terminal</scene> inositol 1,4,5-trisphosphate (InsP₃) binding region, the central modulatory region, and the <scene name='38/382942/C_terminal_domain/1'>carboxy-terminus channel region</scene>.<ref name="mainpaper"/> The protein forms an L-shaped structure composed of two asymmetric domains perpendicular to each other.<ref name="mainpaper"/> The N-terminal domain is made up of 12 β-strands and 2 single-turn helices, which come together to form a barrel.<ref name="mainpaper"/> The C-terminal end is quite different, consisting of a bundle made of eight α-helices.<ref name="mainpaper"/> The interface of the two domains is lined with basic residues and forms the <scene name='38/382942/Ip3_binding_pocket/1'>receptor site</scene> for InsP₃.<ref name="mainpaper"/> The InsP₃R protein does not belong to a superfamily of proteins. The receptor is thought to span the membrane 6 times, leaving the C-terminus in the cytoplasm.<ref name="functionref"/>