Molecular recognition at the myo-inositol 1,4,5-trisphosphate receptor. 3-position substituted myo-inositol 1,4,5-trisphosphate analogues reveal the binding and Ca2+ release requirements for high affinity interaction with the myo-inositol 1,4,5-trisphosphate receptor.
Several novel D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P3] analogues equatorially substituted at the 3-position have been synthesized to probe the structure-activity relationship of the Ins(1,4,5)P3-receptor subsite adjacent to the native 3-hydroxy (3-OH) of Ins(1,4,5)P3. This study was prompted, in part, by our observation that myo-inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4), the 3-position phosphorylated product of Ins(1,4,5)P3 was a full agonist at the Ca(2+)-mobilizing Ins(1,4,5)P3 receptor of SH-SY5Y cells (Wilcox, R.A., Challiss, R. A. J., Liu, C., Potter, B. V. I., and Nahorski, S. R. (1993) Mol. Pharmacol. 44, 810-817). The 3-position Ins(1,4,5)P3 analogues were equatorially substituted with groups spanning the steric range between the 3-OH of Ins(1,4,5)P3 and the 3-phosphate of Ins(1,3,4,5)P4; in order of increasing 3-position steric bulk these were: 3-fluoro-, 3-chloro-, 3-amino-, 3-bromo-, 3-methoxy-, and 3-phosphorothioate-Ins(1,4,5)P3. The analogues were assessed at the specific Ins(1,4,5)P3 binding-site of bovine adrenal cortex and for Ca2+ mobilizing activity in saponin-permeabilized SH-SY5Y human neuroblastoma cells. A correlation was observed between increasing molecular volume of the 3-position substituent and respective decreases in both affinity and Ca2+ mobilizing efficacy. Further analysis of the data also revealed that Ins(1,4,5)P3 analogues with equatorial 3-OH, 3-phosphate, and 3-phosphorothioate substituents interacted more favorably with Ins(1,4,5)P3 recognition sites than would be predicted by purely steric considerations. In contrast, 3-C-trifluoromethyl-Ins(1,4,5)P3 (which is axially substituted, but retains the native 3-OH of Ins(1,4,5)P3) interacted with Ins(1,4,5)P3 recognition sites with virtually the same potency as Ins(1,4,5)P3, indicating that the binding pocket of the Ins(1,4,5)P3-receptor was not sterically restrictive with respect to axially oriented 3-position substituents. We conclude that the Ins(1,4,5)P3 receptor has favorable non-covalent binding interactions with the equatorial 3-position substituents of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 and that these interactions significantly ameliorate the steric constraints of the Ins(1,4,5)P3 receptor binding pocket.
Wilcox
R A
RA
Department of Cell Physiology and Pharmacology, University of Leicester, United Kingdom.
Challiss
R A
RA
Traynor
J R
JR
Fauq
A H
AH
Ognayanov
V I
VI
Kozikowski
A P
AP
Nahorski
S R
SR
D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000737:chemistry / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D009447:Neuroblastoma / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; C081655:inositol-1,3,4,5-tetrakisphosphate; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium