The Pro(335)-> Leu polymorphism of type 3 inositol 1,4,5-trisphosphate receptor found in mouse inbred lines results in functional change

Abstract

Inositol 1,4,5-trisphosphate receptor (IP3R) is an intracellular Ca2+ channel involved in various cellular signaling. Type 3 IP3R (IP(3)R3) retains ligand-gated Ca2+ channel properties differing from other subtypes in terms of IP3-binding affinity and regulation of its channel activity by effector molecules. In this study, we found the natural Pro(335) -> Leu polymorphism of mouse IP(3)R3 between BALB/c and C57BL/6J. We investigated the functional differences between Pro(335)IP(3)R3 and Leu(335)IP(3)R3 with purified receptors reconstituted into proteoliposomes as well as with soluble ligand binding domains. Pro335IP(3)R3 exhibited significantly higher IP3-binding affinity and IP3-induced Ca2+ release than those of Leu335IP(3)R3 in both forms of the receptor. Moreover, the polymorphic change caused differences in the effect of external Ca2+ on IP3-induced Ca2+ release. The Pro335 3 Leu substitution alters the conformation of soluble ligand binding domain as revealed by intrinsic fluorescence and circular dichroism spectra with or without Ca2+. The results indicate that the polymorphism of IP(3)R3 causes changes in receptor function, presumably affecting intracellular Ca2+ signaling.