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Contribution of phosphates and adenine to the potency of adenophostins at the IP₃ receptor: synthesis of all possible bisphosphates of adenophostin A.

Sureshan KM, Riley AM, Thomas MP, Tovey SC, Taylor CW, Potter BV - J. Med. Chem. (2012)

Bottom Line: Compound 6 is the most potent bisphosphate yet discovered with activity at IP(3)R.Thus, adenosine has a direct role independent of the 2'-phosphate group in contributing toward the potency of adenophostins, the vicinal bisphosphate motif is not essential for activity at the IP(3)R, as always thought, and it is possible to design potent agonists with just two of the three phosphates.A model with a possible adenine-R504 interaction supports the activity of 5 and 6 and also allows a reappraisal of the unexpected activity previously reported for the AdA regioisomer 2″-phospho-3″-dephospho-AdA 40.

View Article: PubMed Central - PubMed

Affiliation: Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.

ABSTRACT
Although adenophostin A (AdA), the most potent agonist of d-myo-inositol 1,4,5-trisphosphate receptors (IP(3)R), is thought to mimic IP(3), the relative roles of the different phosphate groups and the adenosine motif have not been established. We synthesized all three possible bisphosphate analogues of AdA and glucose 3,4-bisphosphate (7, AdA lacking the 2'-AMP). 2'-Dephospho-AdA (6) was prepared via a novel regioselective dephosphorylation strategy. Assessment of the abilities of these bisphosphates to stimulate intracellular Ca(2+) release using recombinant rat type 1 IP(3)R (IP(3)R1) revealed that 6, a mimic of Ins(4,5)P(2), is only 4-fold less potent than IP(3), while 7 is some 400-fold weaker and even 3″-dephospho-AdA (5) is measurably active, despite missing one of the vicinal bisphosphate groups normally thought to be crucial for IP(3)-like activity. Compound 6 is the most potent bisphosphate yet discovered with activity at IP(3)R. Thus, adenosine has a direct role independent of the 2'-phosphate group in contributing toward the potency of adenophostins, the vicinal bisphosphate motif is not essential for activity at the IP(3)R, as always thought, and it is possible to design potent agonists with just two of the three phosphates. A model with a possible adenine-R504 interaction supports the activity of 5 and 6 and also allows a reappraisal of the unexpected activity previously reported for the AdA regioisomer 2″-phospho-3″-dephospho-AdA 40.

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Interactions of AdA (A), compound 5 (B), and compound 6 (C) with the IBC of IP3R as predicted by moleculardocking experiments. Waters not shown. Green carbons, α-domain;purple carbons, β-domain. See the ExperimentalSection for details.
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fig8: Interactions of AdA (A), compound 5 (B), and compound 6 (C) with the IBC of IP3R as predicted by moleculardocking experiments. Waters not shown. Green carbons, α-domain;purple carbons, β-domain. See the ExperimentalSection for details.

Mentions: Recently published X-ray structures of the N-terminalligand-bindingdomain (LBD)44 and the N-terminal domainof rat IP3R1 (residues 1–604) with and without IP3 bound support the idea that IP3 causes domainclosure within the IBC.45 As IP3 binds, side chains of nine residues within the α- and β-domainsof the IBC become organized around IP3, causing the clam-likestructure to partially close, reducing the angle between the two domainsby ∼8°. Unfortunately, the resolution of these structuresis not sufficient to provide further clues about how AdA and its analoguesmight bind. The 4,5-bisphosphate of IP3 clearly plays amajor role in cross-linking the two domains of the IBC, and the 1-phosphateexerts its enhancing effect by providing an additional, weaker interactionwith the α-domain, accounting for the greater potency of IP3 relative to Ins(4,5)P2 (Figure 7). The known inactivity of d-myo-inositol 1,4-bisphosphate [Ins(1,4)P2] suggests thatthe 1-P alone cannot interact strongly enough with the α-domainto pull the two domains together. Our model for AdA binding7 shows how the 3″,4″-bisphosphateof AdA can mimic the 4,5-bisphosphate of IP3, while bothits 2′-phosphate group and adenine moiety have additional interactionswith the IBC (Figures 7 and 8A). Specifically, we have proposed that while the 2′-phosphateof AdA essentially mimics the 1-phosphate of IP3, the adeninecan engage in a cation-π interaction with the guanidinium sidechain of R504 in the α-domain.


Contribution of phosphates and adenine to the potency of adenophostins at the IP₃ receptor: synthesis of all possible bisphosphates of adenophostin A.

Sureshan KM, Riley AM, Thomas MP, Tovey SC, Taylor CW, Potter BV - J. Med. Chem. (2012)

Interactions of AdA (A), compound 5 (B), and compound 6 (C) with the IBC of IP3R as predicted by moleculardocking experiments. Waters not shown. Green carbons, α-domain;purple carbons, β-domain. See the ExperimentalSection for details.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3285137&req=5

fig8: Interactions of AdA (A), compound 5 (B), and compound 6 (C) with the IBC of IP3R as predicted by moleculardocking experiments. Waters not shown. Green carbons, α-domain;purple carbons, β-domain. See the ExperimentalSection for details.
Mentions: Recently published X-ray structures of the N-terminalligand-bindingdomain (LBD)44 and the N-terminal domainof rat IP3R1 (residues 1–604) with and without IP3 bound support the idea that IP3 causes domainclosure within the IBC.45 As IP3 binds, side chains of nine residues within the α- and β-domainsof the IBC become organized around IP3, causing the clam-likestructure to partially close, reducing the angle between the two domainsby ∼8°. Unfortunately, the resolution of these structuresis not sufficient to provide further clues about how AdA and its analoguesmight bind. The 4,5-bisphosphate of IP3 clearly plays amajor role in cross-linking the two domains of the IBC, and the 1-phosphateexerts its enhancing effect by providing an additional, weaker interactionwith the α-domain, accounting for the greater potency of IP3 relative to Ins(4,5)P2 (Figure 7). The known inactivity of d-myo-inositol 1,4-bisphosphate [Ins(1,4)P2] suggests thatthe 1-P alone cannot interact strongly enough with the α-domainto pull the two domains together. Our model for AdA binding7 shows how the 3″,4″-bisphosphateof AdA can mimic the 4,5-bisphosphate of IP3, while bothits 2′-phosphate group and adenine moiety have additional interactionswith the IBC (Figures 7 and 8A). Specifically, we have proposed that while the 2′-phosphateof AdA essentially mimics the 1-phosphate of IP3, the adeninecan engage in a cation-π interaction with the guanidinium sidechain of R504 in the α-domain.

Bottom Line: Compound 6 is the most potent bisphosphate yet discovered with activity at IP(3)R.Thus, adenosine has a direct role independent of the 2'-phosphate group in contributing toward the potency of adenophostins, the vicinal bisphosphate motif is not essential for activity at the IP(3)R, as always thought, and it is possible to design potent agonists with just two of the three phosphates.A model with a possible adenine-R504 interaction supports the activity of 5 and 6 and also allows a reappraisal of the unexpected activity previously reported for the AdA regioisomer 2″-phospho-3″-dephospho-AdA 40.

View Article: PubMed Central - PubMed

Affiliation: Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.

ABSTRACT
Although adenophostin A (AdA), the most potent agonist of d-myo-inositol 1,4,5-trisphosphate receptors (IP(3)R), is thought to mimic IP(3), the relative roles of the different phosphate groups and the adenosine motif have not been established. We synthesized all three possible bisphosphate analogues of AdA and glucose 3,4-bisphosphate (7, AdA lacking the 2'-AMP). 2'-Dephospho-AdA (6) was prepared via a novel regioselective dephosphorylation strategy. Assessment of the abilities of these bisphosphates to stimulate intracellular Ca(2+) release using recombinant rat type 1 IP(3)R (IP(3)R1) revealed that 6, a mimic of Ins(4,5)P(2), is only 4-fold less potent than IP(3), while 7 is some 400-fold weaker and even 3″-dephospho-AdA (5) is measurably active, despite missing one of the vicinal bisphosphate groups normally thought to be crucial for IP(3)-like activity. Compound 6 is the most potent bisphosphate yet discovered with activity at IP(3)R. Thus, adenosine has a direct role independent of the 2'-phosphate group in contributing toward the potency of adenophostins, the vicinal bisphosphate motif is not essential for activity at the IP(3)R, as always thought, and it is possible to design potent agonists with just two of the three phosphates. A model with a possible adenine-R504 interaction supports the activity of 5 and 6 and also allows a reappraisal of the unexpected activity previously reported for the AdA regioisomer 2″-phospho-3″-dephospho-AdA 40.

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