Role of protein dynamics in ion selectivity and allosteric coupling in the NaK channel

Proc Natl Acad Sci U S A. 2015 Dec 15;112(50):15366-71. doi: 10.1073/pnas.1515965112. Epub 2015 Nov 30.

Abstract

Flux-dependent inactivation that arises from functional coupling between the inner gate and the selectivity filter is widespread in ion channels. The structural basis of this coupling has only been well characterized in KcsA. Here we present NMR data demonstrating structural and dynamic coupling between the selectivity filter and intracellular constriction point in the bacterial nonselective cation channel, NaK. This transmembrane allosteric communication must be structurally different from KcsA because the NaK selectivity filter does not collapse under low-cation conditions. Comparison of NMR spectra of the nonselective NaK and potassium-selective NaK2K indicates that the number of ion binding sites in the selectivity filter shifts the equilibrium distribution of structural states throughout the channel. This finding was unexpected given the nearly identical crystal structure of NaK and NaK2K outside the immediate vicinity of the selectivity filter. Our results highlight the tight structural and dynamic coupling between the selectivity filter and the channel scaffold, which has significant implications for channel function. NaK offers a distinct model to study the physiologically essential connection between ion conduction and channel gating.

Keywords: ion channels; membrane protein; protein dynamics; solution NMR.

Publication types

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

MeSH terms

  • Allosteric Regulation
  • Bacillus cereus / chemistry*
  • Crystallography, X-Ray
  • Ion Channel Gating
  • Ions
  • Magnetic Resonance Spectroscopy
  • Mutant Proteins / chemistry
  • Point Mutation
  • Potassium / metabolism*
  • Potassium Channels / chemistry*
  • Protein Folding
  • Protein Structure, Secondary
  • Solutions
  • Temperature
  • Time Factors

Substances

  • Ions
  • Mutant Proteins
  • Potassium Channels
  • Solutions
  • Potassium