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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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Hydroxyl groups within the glucose ring of AdA are unimportant.(A–D) Effects of manno-AdA (A) and xylo-AdA (C) on Ca2+ release via each IP3R subtype, and the same analogues compared with AdA (B and D). Results are means ± S.E.M. from 3 independent experiments.
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pone-0058027-g004: Hydroxyl groups within the glucose ring of AdA are unimportant.(A–D) Effects of manno-AdA (A) and xylo-AdA (C) on Ca2+ release via each IP3R subtype, and the same analogues compared with AdA (B and D). Results are means ± S.E.M. from 3 independent experiments.

Mentions: The 5″-CH2OH and 2″-OH substituents of the glucose ring of AdA are thought to mimic the 3-OH and 6-OH of IP3, respectively (Figure 1A). A structure equivalent to the 6-OH of IP3 is an essential feature of all inositol phosphate analogues that bind to IP3R [13], [38], [39] and inversion of its orientation from equatorial to axial reduces affinity by more than 100-fold at all IP3R subtypes [40]. It is therefore surprising, but consistent with previous analyses of native hepatic IP3R [36], that manno-AdA, which differs from AdA only in the orientation of its 2″-OH, should be only 5- to 10-fold less potent than AdA at each IP3R subtype (Figures 4A and B, Tables 1 and 2). Why, when the 6-OH of IP3 and 2″-OH of AdA seem to be analogous in the ligand structures, should these moieties make such different contributions to the interactions of IP3 and AdA with IP3R?


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)

Hydroxyl groups within the glucose ring of AdA are unimportant.(A–D) Effects of manno-AdA (A) and xylo-AdA (C) on Ca2+ release via each IP3R subtype, and the same analogues compared with AdA (B and D). Results are means ± S.E.M. from 3 independent experiments.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585173&req=5

pone-0058027-g004: Hydroxyl groups within the glucose ring of AdA are unimportant.(A–D) Effects of manno-AdA (A) and xylo-AdA (C) on Ca2+ release via each IP3R subtype, and the same analogues compared with AdA (B and D). Results are means ± S.E.M. from 3 independent experiments.
Mentions: The 5″-CH2OH and 2″-OH substituents of the glucose ring of AdA are thought to mimic the 3-OH and 6-OH of IP3, respectively (Figure 1A). A structure equivalent to the 6-OH of IP3 is an essential feature of all inositol phosphate analogues that bind to IP3R [13], [38], [39] and inversion of its orientation from equatorial to axial reduces affinity by more than 100-fold at all IP3R subtypes [40]. It is therefore surprising, but consistent with previous analyses of native hepatic IP3R [36], that manno-AdA, which differs from AdA only in the orientation of its 2″-OH, should be only 5- to 10-fold less potent than AdA at each IP3R subtype (Figures 4A and B, Tables 1 and 2). Why, when the 6-OH of IP3 and 2″-OH of AdA seem to be analogous in the ligand structures, should these moieties make such different contributions to the interactions of IP3 and AdA with IP3R?

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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