Functional basis for calmodulation of the TRPV5 calcium channel

Abstract

Within the transient receptor potential (TRP) superfamily of ion channels, TRPV5 is a highly Ca2+-selective channel important for active reabsorption of Ca2+ in the kidney. Its channel activity is controlled by a negative feedback mechanism involving calmodulin (CaM) binding. Combining advanced microscopy techniques and biochemical assays, this study characterized the dynamic bilobal CaM regulation and binding stoichiometry. We demonstrate for the first time that functional (full-length) TRPV5 interacts with CaM in the absence of Ca2+, and this interaction is intensified at increasing Ca2+ concentrations sensed by the CaM C-lobe that achieves channel pore blocking. Channel inactivation occurs without CaM N-lobe calcification. Moreover, we reveal a 1:2 stoichiometry of TRPV5:CaM binding by implementing single molecule photobleaching counting, a technique with great potential for studying TRP channel regulation. In conclusion, our study proposes a new model for CaM- dependent regulation - calmodulation - of the Ca2+-selective TRPV5 that involves apoCaM interaction and lobe-specific actions.