Activation of IP(3) receptors by synthetic bisphosphate ligands.

Ca(2+) release by d-myo-inositol 1,4,5-trisphosphate receptors (IP(3)Rs) is widely considered to require the vicinal 4,5-bisphosphate motif of IP(3), with P-5 and P-4 engaging the alpha and beta domains of the binding site; using synthesis and mutagenesis we show that the adenine of synthetic glyconucleotides, through an interaction with Arg504, can replace the interaction of either P-1 or P-5 with the alpha-domain producing, respectively, the most potent bisphosphate agonist yet synthesised and the first agonist of IP(3)R without a vicinal bisphosphate motif; this will stimulate new approaches to IP(3)R ligand design.