Functional properties of a pore mutant in the Drosophila melanogaster inositol 1,4,5-trisphosphate receptor.

The inositol (1,4,5)-trisphosphate receptor (InsP3R) is an intracellular calcium release channel that plays a crucial role in cell signaling. In Drosophila melanogaster, a single InsP3R gene (itpr) encodes a protein (DmInsP3R) that is approximately 60% conserved with mammalian InsP3Rs. The functional properties of wild-type (WT) and mutant DmInsP3Rs have recently been described [Srikanth et al., Biophys. J. 86 (2004) 3634-3646]. Here, we use the planar lipid bilayer reconstitution technique to describe single channel properties of a ka901 point mutant (G2630S) in the pore-forming region of DmInsP3R. We find that homomeric ka901 channels are not functional, but the heteromeric WT:ka901 mutant channels display increased conductance, longer channel open time and altered ion selectivity properties when compared to WT DmInsP3R. Obtained results are consistent with the gain of function phenotype observed in ka901/+ mutant flies.