Functional basis for calmodulation of the TRPV5 calcium channel

Within the transient receptor potential (TRP) superfamily of ion channels, TRPV5 is a highly Ca 2+ -selective channel important for active reabsorption of Ca 2+ 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 Ca 2+ , and this interaction is intensified at increasing Ca 2+ 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 Ca 2+ -selective TRPV5 that involves apoCaM interaction and lobe-specific actions.