Ca 2+ -dependent regulation and binding of calmodulin to multiple sites of Transient Receptor Potential Melastatin 3 (TRPM3) ion channels.

TRPM3 proteins assemble to Ca2+ -permeable cation channels in the plasma membrane, which act as nociceptors of noxious heat and mediators of insulin and cytokine release. Here we show that TRPM3 channel activity is strongly dependent on intracellular Ca2+ . Conceivably, this effect is attributed to the Ca2+ binding protein calmodulin, which binds to TRPM3 in a Ca2+ -dependent manner. We identified five calmodulin binding sites within the amino terminus of TRPM3, which displayed different binding affinities in dependence of Ca2+ . Mutations of lysine residues in calmodulin binding site 2 strongly reduced calmodulin binding and TRPM3 activity indicating the importance of this domain for TRPM3-mediated Ca2+ signaling. Our data show that TRPM3 channels are regulated by intracellular Ca2+ and provide the basis for a mechanistic understanding of the regulation of TRPM3 by calmodulin.