HYL-ALPHA-D-GLUCOPYRANOSIDE-2,3',4'-TRISPHOSPHATE, A NOVEL, METABOLICALLY RESISTANT, ADENOPHOSTIN-A AND MYO-INOSITOL-1,4,5-TRISPHOSPHATE ANALOG, POTENTLY INTERACTS WITH THE MYO-INOSITOL-1,4,5-TRISPHOSPHATE RECEPTOR

The novel, synthetic, adenophostin A analogue thyl-alpha-D-glucopyrano side-2,3',4'-trisphosphate [Gluc(2,3',4')P-3] was synthesized to probe the structure-activity relationship at the D-myo-inositol-1,4,5-trisp hosphate [Ins(1,4,5)P-3] receptor [Ins(1,4,5)P(3)R]. This study was st imulated by the recent observation that the fungal isolates adenophost ins A and B were very potent, metabolically resistant, Ins(1,4,5)P(3)R agonists [J. Biol. Chem. 269:369-372 (1994)]. Gluc(2,3',4')P-3 can be visualized as a truncated version of adenophostin A, in which the 2'- and 3'-carbons of the ribose ring, with their terminal phosphate grou ps, are retained and the remainder of the adenosine residue is excised . Gluc(2,3',4')P-3 specifically displaced [H-3]Ins(1,4,5)P-3 from pig cerebellar Ins(1,4,5)P-3 binding sites, with an affinity (IC50 = 130 n M) only 5-fold weaker than that of Ins(1,4,5)P-3 (IC50 = 27 nM). Gluc( 2,3',4')P-3 was also a full agonist for Ca2+ release, being only 10-12 -fold less potent than Ins(1,4,5)P-3 in saponin-permeabilized SH-SY5Y neuro-blastoma cells [EC(50) = 647 nM Ins(1,4,5)P-3 EC(50) = 52 nM] an d Madin-Darby canine kidney cells [EC(50) = 2484 nM; Ins(1,4,5)P-3 EC( 50) = 247 nM]. Gluc(2,3',4')P-3 did not significantly interact with re combinant Ins(1,4,5)P-3 3-kinase and 5-phosphatase enzymes and was als o poorly metabolized by saponin-permeabilized SH-SY5Y cells. However, Gluc(2,3',4')P-3 was a considerably weaker ligand (similar to 500-fold ) and agonist (similar to 1000-fold) than adenophostin A, suggesting t hat the partial excision of the adenosine residue compromised structur al motifs that have favorable interactions with the Ins(1,4,5)P(3)R. I ndeed, molecular dynamics simulations revealed that the potencies of t he three compounds show a correlation with the relative distance of th e two vicinal ring phosphates from the remaining phosphate. Gluc(2,3', 4')P-3, with its alpha-glucoside ring, is the first synthetic Ins(1,4, 5)P-3 analogue that is not structurally based on a phosphorylated inos itol isomer and that exhibits potent activity at the Ins(1,4,5)P(3)R. This, combined with the metabolic resistance of Gluc(2,3',4')P-3, thus affords a novel approach for the investigation of the cellular role o f Ins(1,4,5)P-3 and its receptor.