Electrostatics of ion stabilization in a ClC chloride channel homologue from Escherichia coli

J Mol Biol. 2004 Jun 11;339(4):981-1000. doi: 10.1016/j.jmb.2004.04.023.

Abstract

The structural determinants of electrostatics of ion stabilization within EcClC, a ClC-type chloride channel homologue from Escherichia coli, are studied using a continuum dielectric approximation. Specifically, the ion occupancy is investigated in the wild-type protein and a mutant thereof, and the contribution to the electrostatic binding free energy of local and non-local interactions is characterized at the single-residue level. This analysis shows that, in spite of the desolvation cost and the strong ion-ion repulsion, all previously reported binding sites can be occupied simultaneously. The stabilizing effect of the protein arises from hydrogen bonding as well as from longer-range favorable interactions, such as with the strictly conserved Lys131 side-chain. The latter is involved in the stabilization of the conserved GSGIP motif that delimits two of the binding sites. Interestingly, an additional low-affinity binding site, mediated by a structurally analogous motif including the side-chain of Arg340, can be identified on the extracellular side of the permeation pathway. Finally, it is shown that, in contrast to K-channels, and in analogy to the SBP/PBP sulfate/phosphate-binding proteins, the contribution of helix macrodipoles to chloride binding in EcClC is only marginal.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Chloride Channels / chemistry*
  • Crystallography, X-Ray
  • Escherichia coli / chemistry*
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Conformation
  • Sequence Homology, Amino Acid
  • Static Electricity

Substances

  • Chloride Channels