title: Activation of IP3 receptors requires an endogenous 1-8-14 calmodulin-binding motif.
abstract: Binding of IP3 (inositol 1,4,5-trisphosphate) to the IP3-binding core (residues 224-604) of IP3Rs (IP3 receptors) initiates opening of these ubiquitous intracellular Ca2+ channels. The mechanisms are unresolved, but require conformational changes to pass through the suppressor domain (residues 1-223). A calmodulin-binding peptide derived from myosin light chain kinase uncouples these events. We identified a similar conserved 1-8-14 calmodulin-binding motif within the suppressor domain of IP3R1 and, using peptides and mutagenesis, we demonstrate that it is essential for IP3R activation, whether assessed by IP3-evoked Ca2+ release or patch-clamp recoding of nuclear IP3R. Mimetic peptides specifically inhibit activation of IP3R by uncoupling the IP3-binding core from the suppressor domain. Mutations of key hydrophobic residues within the endogenous 1-8-14 motif mimic the peptides. Our results show that an endogenous 1-8-14 motif mediates conformational changes that are essential for IP3R activation. The inhibitory effects of calmodulin and related proteins may result from disruption of this essential interaction.
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, U.K.
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
authors.forename: Ana M
authors.initials: AM
authors.lastname: Rossi
authors.forename: Taufiq
authors.initials: T
authors.lastname: Rahman
authors.forename: Colin W
authors.initials: CW
authors.lastname: Taylor
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002147:Calmodulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000502:physiology; D011487:Protein Conformation; D051381:Rats
chemical_list: D002147:Calmodulin; D053496:Inositol 1,4,5-Trisphosphate Receptors