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Stimulation of inositol 1,4,5-trisphosphate (IP3) receptor subtypes by adenophostin A and its analogues.

Saleem H, Tovey SC, Riley AM, Potter BV, Taylor CW - PLoS ONE (2013)

Bottom Line: 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 Ca(2+) signals evoked by AdA analogues are unlikely to be due to selective regulation of IP3R subtypes.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Cambridge, United Kingdom.

ABSTRACT
Inositol 1,4,5-trisphosphate receptors (IP3R) are intracellular Ca(2+) 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 Ca(2+) 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 Ca(2+) signals evoked by AdA analogues are unlikely to be due to selective regulation of IP3R subtypes.

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Trimming the adenosine moiety of AdA reduces potency.(A–F) Effects of imidophostin (A), ribophostin (C) and furanophostin (E) on Ca2+ release via each of the three IP3R subtypes, and the same analogues compared with AdA (B, D and F). Results are means ± S.E.M. from 3 independent experiments. (G) A cation-π interaction between the adenine of AdA and R504 within the α-domain of the IBC is proposed to stabilize AdA binding (left). Closure of the clam-like IBC is proposed to be mediated by interactions between the 3″-phosphate of AdA and the α-domain of the IBC (blue ribbon), and between the 4″-phosphate and the β-domain of the IBC (green ribbon). In 3″-dephospho AdA, a cation-π interaction between AdA and the IBC α-domain is proposed to be sufficient to allow some effective closure of the clam. R504 is conserved in all three mammalian IP3R subtypes (right).
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pone-0058027-g003: Trimming the adenosine moiety of AdA reduces potency.(A–F) Effects of imidophostin (A), ribophostin (C) and furanophostin (E) on Ca2+ release via each of the three IP3R subtypes, and the same analogues compared with AdA (B, D and F). Results are means ± S.E.M. from 3 independent experiments. (G) A cation-π interaction between the adenine of AdA and R504 within the α-domain of the IBC is proposed to stabilize AdA binding (left). Closure of the clam-like IBC is proposed to be mediated by interactions between the 3″-phosphate of AdA and the α-domain of the IBC (blue ribbon), and between the 4″-phosphate and the β-domain of the IBC (green ribbon). In 3″-dephospho AdA, a cation-π interaction between AdA and the IBC α-domain is proposed to be sufficient to allow some effective closure of the clam. R504 is conserved in all three mammalian IP3R subtypes (right).

Mentions: Systematic trimming of the adenosine moiety of AdA successively produces imidophostin (which lacks the pyrimidine ring of AdA), ribophostin (in which a methoxy group replaces the adenine moiety of AdA) and furanophostin (in which only the furanoid ring remains) (Figure 1A). Maximally effective concentrations of each of these analogues released the same fraction of the intracellular Ca2+ stores as AdA in cells expressing each of the three IP3R subtypes, and each analogue was ∼5-10-fold less potent than AdA (Figure 3, Tables 1 and 2). These results are consistent with previous analyses of IP3R in hepatocytes, which express predominantly IP3R2 [24], [36], with analyses of binding of ribophostin and furanophostin to an N-terminal fragment of IP3R1 [12], and with evidence from other analogues that trimming the adenosine moiety decreases affinity for cerebellar IP3R, which are largely IP3R1 [37].


Stimulation of inositol 1,4,5-trisphosphate (IP3) receptor subtypes by adenophostin A and its analogues.

Saleem H, Tovey SC, Riley AM, Potter BV, Taylor CW - PLoS ONE (2013)

Trimming the adenosine moiety of AdA reduces potency.(A–F) Effects of imidophostin (A), ribophostin (C) and furanophostin (E) on Ca2+ release via each of the three IP3R subtypes, and the same analogues compared with AdA (B, D and F). Results are means ± S.E.M. from 3 independent experiments. (G) A cation-π interaction between the adenine of AdA and R504 within the α-domain of the IBC is proposed to stabilize AdA binding (left). Closure of the clam-like IBC is proposed to be mediated by interactions between the 3″-phosphate of AdA and the α-domain of the IBC (blue ribbon), and between the 4″-phosphate and the β-domain of the IBC (green ribbon). In 3″-dephospho AdA, a cation-π interaction between AdA and the IBC α-domain is proposed to be sufficient to allow some effective closure of the clam. R504 is conserved in all three mammalian IP3R subtypes (right).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585173&req=5

pone-0058027-g003: Trimming the adenosine moiety of AdA reduces potency.(A–F) Effects of imidophostin (A), ribophostin (C) and furanophostin (E) on Ca2+ release via each of the three IP3R subtypes, and the same analogues compared with AdA (B, D and F). Results are means ± S.E.M. from 3 independent experiments. (G) A cation-π interaction between the adenine of AdA and R504 within the α-domain of the IBC is proposed to stabilize AdA binding (left). Closure of the clam-like IBC is proposed to be mediated by interactions between the 3″-phosphate of AdA and the α-domain of the IBC (blue ribbon), and between the 4″-phosphate and the β-domain of the IBC (green ribbon). In 3″-dephospho AdA, a cation-π interaction between AdA and the IBC α-domain is proposed to be sufficient to allow some effective closure of the clam. R504 is conserved in all three mammalian IP3R subtypes (right).
Mentions: Systematic trimming of the adenosine moiety of AdA successively produces imidophostin (which lacks the pyrimidine ring of AdA), ribophostin (in which a methoxy group replaces the adenine moiety of AdA) and furanophostin (in which only the furanoid ring remains) (Figure 1A). Maximally effective concentrations of each of these analogues released the same fraction of the intracellular Ca2+ stores as AdA in cells expressing each of the three IP3R subtypes, and each analogue was ∼5-10-fold less potent than AdA (Figure 3, Tables 1 and 2). These results are consistent with previous analyses of IP3R in hepatocytes, which express predominantly IP3R2 [24], [36], with analyses of binding of ribophostin and furanophostin to an N-terminal fragment of IP3R1 [12], and with evidence from other analogues that trimming the adenosine moiety decreases affinity for cerebellar IP3R, which are largely IP3R1 [37].

Bottom Line: 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 Ca(2+) signals evoked by AdA analogues are unlikely to be due to selective regulation of IP3R subtypes.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Cambridge, United Kingdom.

ABSTRACT
Inositol 1,4,5-trisphosphate receptors (IP3R) are intracellular Ca(2+) 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 Ca(2+) 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 Ca(2+) signals evoked by AdA analogues are unlikely to be due to selective regulation of IP3R subtypes.

Show MeSH
Related in: MedlinePlus