Molecular Recognition of Adenophostin, a Very Potent Ca²⁺ Inducer, at the d-myo-Inositol 1,4,5-Trisphosphate Receptor

Abstract

The recognition mode of adenophostin A at the D-myo-inositol 1,4, 5-trisphosphate [Ins(1,4,5)P(3)] receptor was investigated. Comparison of conformations of Ins(1,4,5)P(3) and adenophostin A by using the combination of NMR and molecular mechanics (MM) calculations demonstrated that adenophostin A adopted a moderately extended conformation regarding the distance between the 2'-phosphoryl group and the 3' ',4' '-bisphosphate motif, as suggested previously [Wilcox, R. A. et al. (1995) Mol. Pharmacol. 47, 1204-1211]. Based on the nuclear Overhauser effect (NOE) observed between 3'-H and 1' '-H and on MM calculations, the molecular shape of adenophostin A proved to be an extended form at least in solution, in contrast to Wilcox's compactly folded, preliminary hairpin model. GlcdR(2,3',4')P(3), an adenophostin analogue without adenine moiety, was found to be less potent than adenophostin A and almost equipotent to Ins(1,4,5)P(3). We propose the possibility that (i) the optimal spatial arrangement of the three phosphoryl groups and/or (ii) the interaction of the adenine moiety of adenophostin A with the putative binding site, if it exists in the vicinity of the Ins(1,4,5)P(3)-binding site, might account for the exceptional potency of adenophostin A.

Selective determinants of inositol 1,4,5‐trisphosphate and adenophostin A interactions with type 1 inositol 1,4,5‐trisphosphate receptors

“…Inositol 1,4,5‐trisphosphate and AdA are each full agonists of the IP 3 R (Rossi et al ., 2009). Both IP 3 and AdA bind to the IBC, and despite their structural differences, the 3",4"‐bisphosphate and 2"‐hydroxyl groups of AdA evidently mimic the essential 4,5‐bisphosphate and 6‐hydroxyl of IP 3 (Figure 1B) (Takahashi et al ., 1994c; Hotoda et al ., 1999; Correa et al ., 2001; Rosenberg et al ., 2003). These features probably account for the binding of AdA to the IBC (Rosenberg et al ., 2003), but they do not explain the ability of AdA to bind to IP 3 R with greater affinity than IP 3 .…”

Activation of IP3 receptors by synthetic bisphosphate ligands

“…It binds to a site that substantially overlaps the IP 3 -binding site, 6 and structure–activity studies with synthetic analogues of AdA have established that the adenine (or another aromatic group) is essential for its enhanced affinity. 6,7 …”

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

“…It has been suggested that the 2′-phosphate of AdA interacts with the IBC in a manner that allows it to behave as a super-optimal mimic of the 1-phosphate of IP 3 [44], [45]. However, our recent study combining structure-activity analyses with mutagenesis of the binding site suggest that the 1-phosphate of IP 3 is more important for binding than is the 2′-phosphate of AdA [12].…”