Functional basis for calmodulation of the TRPV5 calcium channel

• Published in: The Journal of physiology 2023-02, Vol.601 (4), p.859-878
• Main Authors: Zuidscherwoude, Malou, Goor, Mark K., Roig, Sara R., Thijssen, Niky, Erp, Merijn, Fransen, Jack, Wijst, Jenny, Hoenderop, Joost G.
• Format: Article
• Language: English
• Subjects: Calcification; calcium; Calcium - metabolism; Calcium Channels - metabolism; Calcium homeostasis; Calcium transport; Calcium-binding protein; Calmodulin; Calmodulin - metabolism; Channel gating; channel regulation; Feedback; Fluorescence microscopy; Homeostasis; Ion channels; Kidneys; Microscopy; Protein Binding; Reabsorption; single molecule; Stoichiometry; Transient receptor potential proteins; TRP channel; TRPV Cation Channels - metabolism
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/JP282952

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 lobe‐specific CaM regulation. 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 requiring CaM N‐lobe calcification. Moreover, we show a Ca2+‐dependent binding stoichiometry at the single channel level. In conclusion, our study proposes a new model for CaM‐dependent regulation – calmodulation – of this uniquely Ca2+‐selective TRP channel TRPV5 that involves apoCaM interaction and lobe‐specific actions, which may be of significant physiological relevance given its role as gatekeeper of Ca2+ transport in the kidney. Key points The renal Ca2+ channel TRPV5 is an important player in maintenance of the body's Ca2+ homeostasis. Activity of TRPV5 is controlled by a negative feedback loop that involves calmodulin (CaM), a protein with two Ca2+‐binding lobes. We investigated the dynamics of the interaction between TRPV5 and CaM with advanced fluorescence microscopy techniques. Our data support a new model for CaM‐dependent regulation of TRPV5 channel activity with CaM lobe‐specific actions and demonstrates Ca2+‐dependent binding stoichiometries. This study improves our understanding of the mechanism underlying fast channel inactivation, which is physiologically relevant given the gatekeeper function of TRPV5 in Ca2+ reabsorption in the kidney. figure legend Calmodulation of the epithelial calcium channel TRPV5. The Ca2+ concentration modulates calmodulin‐dependent inhibition of TRPV5. The three panels depict key moments in a continuum of increasing Ca2+ concentration (gradient slider under the panels). The left panel shows a situation where Ca2+ is virtually absent and CaM is in its apo‐CaM conformation. The interaction between TRPV5 and apo‐CaM does not rely on the presence of Ca2+ even though CaM‐dependent inhibition of TRPV5 is compromised. The middle panel depicts a physiologically relevant Ca2+ concentration where one or both lobes of CaM are calcified and the TR