The inositol 1,4,5-trisphosphate receptor (InsP3R) is activated by InsP3 binding to amino-terminal ligand binding domain (InsP3R-N). Recently we reported functional coupling of phosphatidylinositol (4,5)-bisphosphate (PIP2) to the InsP3R. Specific binding of PIP2 to InsP3R-N domain was postulated as a part of the InsP3R-PIP2 functional coupling model. Here we utilized bacterially expressed and purified InsP3R-N domain to characterize its binding specificity for InsP3, Adenophostin A (AdA) and the water, soluble PIP2 analog dioctanoyl-(4,5)PIP2 (ShPIP2). Obtained data led us to conclude that specific InsP3, AdA, and ShPIP2 binding sites are located within the InsP3R-N domain, that the extra receptor binding element responsible for enhanced binding of AdA is an integral part of the InsP3R-N domain, that ShPIP2 is able to displace InsP3 from the InsP3R-N, but InsP3 or AdA is unable to completely displace ShPIP2. These results support the InsP3R-PIP2 functional coupling model and provide novel insights into InsP3R ligand specificity. (C) 2000 Academic Press.
ASJC Scopus subject areas
- Molecular Biology