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

Abstract

Inositol 1,4,5-trisphosphate receptors (IP3R) are intracellular Ca2+ channels. Most animal cells express mixtures of the three IP3R subtypes encoded by vertebrate genomes. Adenophostin A (AdA) is the most potent naturally occurring agonist of IP3R and it shares with IP3 the essential features of all IP3R agonists, namely structures equivalent to the 4,5-bisphosphate and 6-hydroxyl of IP3. The two essential phosphate groups contribute to closure of the clam-like IP3-binding core (IBC), and thereby IP3R activation, by binding to each of its sides (the α- and β-domains). Regulation of the three subtypes of IP3R by AdA and its analogues has not been examined in cells expressing defined homogenous populations of IP3R. We measured Ca2+ release evoked by synthetic adenophostin A (AdA) and its analogues in permeabilized DT40 cells devoid of native IP3R and stably expressing single subtypes of mammalian IP3R. The determinants of high-affinity binding of AdA and its analogues were indistinguishable for each IP3R subtype. The results are consistent with a cation-π interaction between the adenine of AdA and a conserved arginine within the IBC α-domain contributing to closure of the IBC. The two complementary contacts between AdA and the α-domain (cation-π interaction and 3″-phosphate) allow activation of IP3R by an analogue of AdA (3″-dephospho-AdA) that lacks a phosphate group equivalent to the essential 5-phosphate of IP3. These data provide the first structure-activity analyses of key AdA analogues using homogenous populations of all mammalian IP3R subtypes. They demonstrate that differences in the Ca2+ signals evoked by AdA analogues are unlikely to be due to selective regulation of IP3R subtypes.

Interactions of antagonists with subtypes of inositol 1,4,5‐trisphosphate (IP3) receptor

“…The slope of the Schild plots was 1.14 ± 0.41 ( n = 3) and the K D for heparin was 2.8 μg·mL −1 (pK D = 5.55 ± 0.09) (Figure 2D and Table 1). AdA has ∼10-fold higher affinity than IP 3 for all three IP 3 R subtypes (Table 1) (Rossi et al ., 2010a; Saleem et al ., 2013), and we have shown that the affinity of heparin for IP 3 R1 is similar whether IP 3 or AdA is used to evoke Ca 2+ release (Figure 1B–E). To obtain an independent measure of the affinity of IP 3 R3 for heparin, free of the problems associated with using IP 3 , we therefore repeated the Schild analysis using AdA to stimulate Ca 2+ release.…”

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

“…[245] Recent data have also focussed upon receptor subtypes in concert with adenophostin analogues. [246] Designing simple synthetic modulators of the Ins(1,4,5)P 3 receptor not based upon inositol that would mimic a myoinositol polyphosphate has always been achallenge.Since the publication of the first antagonist lead, biphenyl 2,3',4,5',6pentakisphosphate BiPh(2,3',4,5',6)P 5 ,( 262;F igure 15), [247] which also exhibits other biological activities, [248] similar compounds have been reported that explore the growing potential of benzene polyphosphates in cell-signaling applications.T hus,anoncarbohydrate/inositol phosphate Ins-(1,4,5)P 3 receptor agonist, based upon ab iphenyl structure and decorated with phosphate groups-biphenyl 3,3',4,4',5,5'hexakisphosphate (BiPh(3,3',4,4',5,5')P 6 , 263)-has been syn-…”

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

“…[245] Recent data have also focussed upon receptor subtypes in concert with adenophostin analogues. [246] There has always been the challenge to design simple synthetic modulators of the Ins(1,4,5)P 3 receptor not based upon inositol that would mimic a myo-inositol polyphosphate. Since the publication of the first antagonist lead, biphenyl 2,3′,4,5′,6-pentakisphosphate BiPh(2,3′,4,5′,6)P 5 , (262 in Figure 15), [247] which also exhibits other biological activities, [248] …”

“…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 . Recent data have also focussed upon receptor subtypes in concert with adenophostin analogues …”