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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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AdA is a potent agonist of all three IP3 receptor subtypes.(A) Concentration-dependent effects of AdA on Ca2+ release from the intracellular stores of cells expressing IP3R1, IP3R2 or IP3R3. All results are expressed as percentages of the Ca2+ release evoked by ionomycin. The same colour codes are used in all subsequent figures. (B) Comparison, for each IP3R subtype, of the Ca2+ release evoked by IP3 and AdA. Results are means ± SEM from the number of independent experiments given in Table 1. Here, and in many subsequent figures, some error bars are smaller than the symbols.
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pone-0058027-g002: AdA is a potent agonist of all three IP3 receptor subtypes.(A) Concentration-dependent effects of AdA on Ca2+ release from the intracellular stores of cells expressing IP3R1, IP3R2 or IP3R3. All results are expressed as percentages of the Ca2+ release evoked by ionomycin. The same colour codes are used in all subsequent figures. (B) Comparison, for each IP3R subtype, of the Ca2+ release evoked by IP3 and AdA. Results are means ± SEM from the number of independent experiments given in Table 1. Here, and in many subsequent figures, some error bars are smaller than the symbols.

Mentions: The results shown in Figure 2 and Tables 1 and 2 demonstrate that AdA is ∼10-times more potent than IP3 at each IP3R subtype, and for each subtype, maximally effective concentrations of IP3 and AdA release the same fraction of the intracellular Ca2+ stores. This is consistent with many analyses of IP3 and AdA in a variety of cell types using both functional and binding assays, in which AdA behaves as a full agonist with ∼10-fold greater affinity than IP3 [reviewed in 8]. Our results do, however, provide the first direct demonstration that AdA interacts similarly with all three IP3R subtypes. Subsequent experiments examine the interactions between key analogues of IP3 and AdA with each IP3R subtype.


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)

AdA is a potent agonist of all three IP3 receptor subtypes.(A) Concentration-dependent effects of AdA on Ca2+ release from the intracellular stores of cells expressing IP3R1, IP3R2 or IP3R3. All results are expressed as percentages of the Ca2+ release evoked by ionomycin. The same colour codes are used in all subsequent figures. (B) Comparison, for each IP3R subtype, of the Ca2+ release evoked by IP3 and AdA. Results are means ± SEM from the number of independent experiments given in Table 1. Here, and in many subsequent figures, some error bars are smaller than the symbols.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585173&req=5

pone-0058027-g002: AdA is a potent agonist of all three IP3 receptor subtypes.(A) Concentration-dependent effects of AdA on Ca2+ release from the intracellular stores of cells expressing IP3R1, IP3R2 or IP3R3. All results are expressed as percentages of the Ca2+ release evoked by ionomycin. The same colour codes are used in all subsequent figures. (B) Comparison, for each IP3R subtype, of the Ca2+ release evoked by IP3 and AdA. Results are means ± SEM from the number of independent experiments given in Table 1. Here, and in many subsequent figures, some error bars are smaller than the symbols.
Mentions: The results shown in Figure 2 and Tables 1 and 2 demonstrate that AdA is ∼10-times more potent than IP3 at each IP3R subtype, and for each subtype, maximally effective concentrations of IP3 and AdA release the same fraction of the intracellular Ca2+ stores. This is consistent with many analyses of IP3 and AdA in a variety of cell types using both functional and binding assays, in which AdA behaves as a full agonist with ∼10-fold greater affinity than IP3 [reviewed in 8]. Our results do, however, provide the first direct demonstration that AdA interacts similarly with all three IP3R subtypes. Subsequent experiments examine the interactions between key analogues of IP3 and AdA with each IP3R subtype.

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