Crystal structure of full-length KcsA in its closed conformation

Proc Natl Acad Sci U S A. 2009 Apr 21;106(16):6644-9. doi: 10.1073/pnas.0810663106. Epub 2009 Apr 3.


KcsA is a proton-activated, voltage-modulated K(+) channel that has served as the archetype pore domain in the Kv channel superfamily. Here, we have used synthetic antigen-binding fragments (Fabs) as crystallographic chaperones to determine the structure of full-length KcsA at 3.8 A, as well as that of its isolated C-terminal domain at 2.6 A. The structure of the full-length KcsA-Fab complex reveals a well-defined, 4-helix bundle that projects approximately 70 A toward the cytoplasm. This bundle promotes a approximately 15 degree bending in the inner bundle gate, tightening its diameter and shifting the narrowest point 2 turns of helix below. Functional analysis of the full-length KcsA-Fab complex suggests that the C-terminal bundle remains whole during gating. We suggest that this structure likely represents the physiologically relevant closed conformation of KcsA.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry*
  • Crystallography, X-Ray
  • Immunoglobulin Fab Fragments / chemistry
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation / genetics
  • Peptide Library
  • Potassium Channels / chemistry*
  • Protein Binding
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Streptomyces lividans / chemistry*


  • Bacterial Proteins
  • Immunoglobulin Fab Fragments
  • Peptide Library
  • Potassium Channels
  • prokaryotic potassium channel

Associated data

  • PDB/3EFD
  • PDB/3EFF