Calcium-induced conformational changes in C-terminal tail of polycystin-2 are necessary for channel gating

J Biol Chem. 2012 May 18;287(21):17232-17240. doi: 10.1074/jbc.M112.354613. Epub 2012 Apr 3.

Abstract

Polycystin-2 (PC2) is a Ca(2+)-permeable transient receptor potential channel activated and regulated by changes in cytoplasmic Ca(2+). PC2 mutations are responsible for ∼15% of autosomal dominant polycystic kidney disease. Although the C-terminal cytoplasmic tail of PC2 has been shown to contain a Ca(2+)-binding EF-hand domain, the molecular basis of PC2 channel gating by Ca(2+) remains unknown. We propose that the PC2 EF-hand is a Ca(2+) sensor required for channel gating. Consistent with this, Ca(2+) binding causes a dramatic decrease in the radius of gyration (R(g)) of the PC2 EF-hand by small angle x-ray scattering and significant conformational changes by NMR. Furthermore, increasing Ca(2+) concentrations cause the C-terminal cytoplasmic tail to transition from a mixture of extended oligomers to a single compact dimer by analytical ultracentrifugation, coupled with a >30 Å decrease in maximum interatomic distance (D(max)) by small angle x-ray scattering. Mutant PC2 channels unable to bind Ca(2+) via the EF-hand are inactive in single-channel planar lipid bilayers and inhibit Ca(2+) release from ER stores upon overexpression in cells, suggesting dominant negative properties. Our results support a model where PC2 channels are gated by discrete conformational changes in the C-terminal cytoplasmic tail in response to changes in cytoplasmic Ca(2+) levels. These properties of PC2 are lost in autosomal dominant polycystic kidney disease, emphasizing the importance of PC2 to kidney cell function. We speculate that PC2 and the Ca(2+)-dependent transient receptor potential channels in general are regulated by similar conformational changes in their cytoplasmic domains that are propagated to the channel pore.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / chemistry*
  • Calcium / metabolism*
  • Cell Line
  • Crystallography, X-Ray
  • Humans
  • Ion Channel Gating / physiology*
  • Models, Biological*
  • Models, Molecular*
  • Protein Structure, Tertiary
  • TRPP Cation Channels / chemistry*
  • TRPP Cation Channels / genetics
  • TRPP Cation Channels / metabolism*

Substances

  • TRPP Cation Channels
  • polycystic kidney disease 2 protein
  • Calcium