Stimulation of Inositol 1,4,5-Trisphosphate (IP3) Receptor Subtypes by Analogues of IP3

Abstract

Most animal cells express mixtures of the three subtypes of inositol 1,4,5-trisphosphate receptor (IP3R) encoded by vertebrate genomes. Activation of each subtype by different agonists has not hitherto been examined in cells expressing defined homogenous populations of IP3R. Here we measure Ca2+ release evoked by synthetic analogues of IP3 using a Ca2+ indicator within the lumen of the endoplasmic reticulum of permeabilized DT40 cells stably expressing single subtypes of mammalian IP3R. Phosphorylation of (1,4,5)IP3 to (1,3,4,5)IP4 reduced potency by ∼100-fold. Relative to (1,4,5)IP3, the potencies of IP3 analogues modified at the 1-position (malachite green (1,4,5)IP3), 2-position (2-deoxy(1,4,5)IP3) or 3-position (3-deoxy(1,4,5)IP3, (1,3,4,5)IP4) were similar for each IP3R subtype. The potency of an analogue, (1,4,6)IP3, in which the orientations of the 2- and 3-hydroxyl groups were inverted, was also reduced similarly for all three IP3R subtypes. Most analogues of IP3 interact similarly with the three IP3R subtypes, but the decrease in potency accompanying removal of the 1-phosphate from (1,4,5)IP3 was least for IP3R3. Addition of a large chromophore (malachite green) to the 1-phosphate of (1,4,5)IP3 only modestly reduced potency suggesting that similar analogues could be used to measure (1,4,5)IP3 binding optically. These data provide the first structure-activity analyses of key IP3 analogues using homogenous populations of each mammalian IP3R subtype. They demonstrate broadly similar structure-activity relationships for all mammalian IP3R subtypes and establish the potential utility of (1,4,5)IP3 analogues with chromophores attached to the 1-position.

Subtype-selective regulation of IP3 receptors by thimerosal via cysteine residues within the IP3-binding core and suppressor domain

“…Furthermore, IP 3 R with cysteine-less NT are not constitutively active and respond normally to IP 3 [6]. We also used algorithms that predict the accessibility [51] and reactivity [52] of cysteine residues together with modelled structures of NT2–NT3 [53] to identify cysteine residues that might account for the differential sensitivities of IP 3 R1–IP 3 R3 to thimerosal. The results suggest that within the SD, there are two accessible cysteine residues (Cys 206 and Cys 214 in IP 3 R1) and they are predicted to be equally accessible in all three subtypes, but the residue equivalent to Cys 214 in IP 3 R1 is less reactive in IP 3 R3 (Supplementary Figure S2).…”

Ca2+homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles

“…The "brain" type, RyR3, is mainly distributed in the hippocampal CA1 pyramidal cell layer, the basal ganglia, and olfactory bulbs (131)(132)(133). IP 3 R is a ligand-gated Ca 2+ -release channel, activated by IP 3 , a second messenger involved in G-protein-coupled signal transduction (134). The cytosolic and luminal Ca 2+ concentration also regulates the activity of IP 3 R (127).…”

The “Other” Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances inmyo‐Inositol Chemistry)

“…Recent data have provided the first structure-activity analyses of key Ins(1,4,5)P 3 analogues using homogenous populations of each mammalian Ins(1,4,5)P 3 R subtype. [238] Other myo-inositol phosphate analogues have been synthesized that may provide new mechanistic insights and structure-activity relationship information for the inositol trisphosphate receptor. Inositol 1,4,5-trisphosphate analogues in which the 5-phosphate was replaced with less acidic bioisosteres have been synthesized.…”

“…Recent data have provided structure-activity analyses of homologous populations of all mammalian receptor subtypes. [238] Additionally, there has been much interest in synthetic glyconucleotides based upon the naturally-occurring adenophostins, where the pharmacophore presented to the receptor is comprised of a combination of a phosphorylated carbohydrate and a pendant group that can be a nucleotide or other motif. [245] Recent data have also focussed upon receptor subtypes in concert with adenophostin analogues.…”