Structural basis of TRPV5 regulation by physiological and pathophysiological modulators

Area of Science:

• Molecular biology
• Biophysics
• Physiology

Background:

• Transient receptor potential vanilloid 5 (TRPV5) is a crucial kidney ion channel for calcium homeostasis.
• TRPV5 activity is modulated by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and calcium-bound calmodulin (CaM).
• Parathyroid hormone (PTH) regulates TRPV5 activity via protein kinase A (PKA) phosphorylation.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying TRPV5 regulation by low pH and PKA.
• To investigate how metabolic acidosis affects TRPV5 activity.
• To understand the interplay between PI(4,5)P2, CaM, and PKA in controlling TRPV5 gating.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine TRPV5 structures at low pH.
• Biochemical assays to assess protein-protein interactions and channel activity.
• Functional studies to evaluate the impact of PKA phosphorylation and PI(4,5)P2 on TRPV5 gating.

Main Results:

• Low pH inhibits TRPV5 by preventing PI(4,5)P2 binding and activation.
• Cryo-EM revealed intermediate conformations of TRPV5 at low pH, illustrating the open-to-closed transition.
• PI(4,5)P2 is identified as the primary gating modulator, while PKA phosphorylation inhibits CaM binding and channel inactivation.

Conclusions:

• Metabolic acidosis reduces TRPV5 activity by inhibiting PI(4,5)P2-mediated activation, leading to hypercalciuria.
• PKA phosphorylation is a key mechanism for preventing TRPV5 channel inactivation by CaM.
• The study provides detailed molecular insights into the regulation of TRPV5 by pH and PKA, crucial for calcium homeostasis.