Structure of a novel InsP3 receptor.

Abstract

Inositol 1,4,5‐trisphosphate (InsP3) constitutes a major intracellular second messenger that transduces many growth factor and neurotransmitter signals. InsP3 causes the release of Ca2+ from intracellular stores by binding to specific receptors that are coupled to Ca2+ channels. One such receptor from cerebellum has previously been extensively characterized. We have now determined the full structure of a second, novel InsP3 receptor which we refer to as type 2 InsP3 receptor as opposed to the cerebellar type 1 InsP3 receptor. The type 2 InsP3 receptor has the same general structural design as the cerebellar type 1 InsP3 receptor with which it shares 69% sequence identity. Expression of the amino‐terminal 1078 amino acids of the type 2 receptor demonstrates high affinity binding of InsP3 to the type 2 receptor with a similar specificity but higher affinity than observed for the type 1 receptor. These results demonstrate the presence of several types of InsP3 receptor in brain and raise the possibility that intracellular Ca2+ signaling may involve multiple pathways with different regulatory properties dependent on different InsP3 receptors.

Functional Consequences of Phosphomimetic Mutations at Key cAMP-dependent Protein Kinase Phosphorylation Sites in the Type 1 Inositol 1,4,5-Trisphosphate Receptor

“…2D), CCh-induced Ca 2ϩ release in the S2Ϫ EE mutant (EC 50 4.3 Ϯ 1.2 nM CCh) was 7.5-fold more sensitive when compared with WT S2Ϫ InsP 3 R-1 (EC 50 ϭ 32.6 Ϯ 7.5 nM) and some 50-fold more sensitive than the nonphosphorylatable S2Ϫ AA mutant (EC 50 ϭ 229.5 Ϯ 14.6 nM). These data provide strong evidence that the S2Ϫ EE construct is more sensitive to stimulation by InsP 3 and present evidence that phosphorylation of the InsP 3 R-1 results in marked regulation of channel function. This profound regulation could be expected to have major consequences for calcium signaling events in peripheral tissue such as liver, testis, and smooth muscle which express the S2Ϫ InsP 3 R-1 (5, 6).…”

“…These data indicate that serine to glutamate mutations at the functionally important phosphorylation sites in both splice variants of InsP 3 R-1 are "phosphomimetic," i.e. charge mutations mimic phosphorylation in that these constructs display an apparent increased functional sensitivity to InsP 3 . ] i response to stimulation with CCh does not appreciably desensitize, and thus the effects of multiple concentrations of agonist can be assessed in a single cell.…”

“…Each subunit has a binding site for InsP 3 toward the N terminus formed by a cluster of positively charged amino acids thought to coordinate the negatively charged phosphate groups of InsP 3 (11,12). The C terminus of each subunit is postulated to span intracellular membranes six times and forms a single cation-selective pore (13,14).…”

Calcium‐induced degradation of the Inositol (1,4,5)‐trisphosphate receptor/Ca2+‐channel

“…The isoforms of the IP,-receptor, all of which have approximate molecular masses of 260 kilodalton (kDa) when analysed by SDS-PAGE [4,5], contain both a cytoplasmic IP,-binding domain and a transmembrane Ca"-channel domain [6,7]. Binding of IP, to the cytoplasmic receptor domain induces Ca" flux through the channel domain and thereby leads to increases in cytoplasmic [Ca"] [8,9].…”

Subunit Oligomerization, and Topology of the Inositol 1,4,5-Trisphosphate Receptor

“…Plasma membrane receptor-coupled activation of G-protein or tyrosine kinase-induced hydrolysis of phosphotidylinositol 4,5-bisphosphate results in the production of InsP 3 and subsequent efflux of Ca 2ϩ from endoplasmic reticulum stores. InsP 3 -mediated calcium release has been implicated in numerous, very diverse cellular processes including the initiation/propagation of Ca 2ϩ waves, cell growth, secretion, fertilization, and development (1,2).…”