The distal C-terminal region of the KcsA potassium channel is a pH-dependent tetramerization domain

Guy Kamnesky, Hadassa Shaked, Jordan H. Chill

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8 Scopus citations


The intracellular C-terminal domain (CTD) of KcsA, a bacterial homotetrameric potassium channel, is a 40-residue-long segment that natively adopts a helical bundle conformation with 4-fold symmetry. A hallmark of KcsA behavior is pH-induced conformational change, which leads to the opening of the channel at acidic pH. Previous studies have reached conflicting conclusions as to the role of the CTD in this transition. Here, we investigate the involvement of this domain in pH-mediated channel opening by NMR using a soluble peptide corresponding to residues 128-160 of the CTD (CTD34). At neutral pH, CTD34 exhibits concentration-dependent spectral changes consistent with oligomer formation. We prove this slowly tumbling species to be a tetramer with a dissociation constant of (2.0 ± 0.5) × 10-11 M3 by NMR and sedimentation equilibrium experiments. Whereas monomeric CTD34 is only mildly helical, secondary chemical shifts prove that the tetrameric species adopts a tight native-like helical bundle conformation. The tetrameric species undergoes pH-dependent dissociation, and CTD34 is fully monomeric below pH 5.0. The structural basis for this phenomenon is the destabilization of the tetrameric CTD34 by protonation of residue H145 in the monomeric form of the peptide. We conclude that (i) the CTD34 peptide is independently capable of forming a tetrameric helical bundle, and (ii) this structurally significant conformational shift is modulated by the effects of solution pH on residue H145. Therefore, the involvement of this domain in the pH gating of the channel is strongly suggested.

Original languageEnglish
Pages (from-to)237-247
Number of pages11
JournalJournal of Molecular Biology
Issue number3-4
StatePublished - 4 May 2012

Bibliographical note

Funding Information:
We thank H. Gottlieb and K. Keinan-Adamsky for assistance with the use of the spectrometer, R. Persky for mass spectrometry analyses, D. Major for the nonlinear least-squares fitting program, S. Rahimipour for the use of his HPLC system, D. Fass and E. Schnur (Weizmann Institute of Science) and A. Abdussalam and A. Vitlin (Tel Aviv University) for assistance with SE measurements, and Y. Paas (Bar Ilan University), F. Naider (Staten Island, CUNY), and L. Kay (University of Toronto) for discussions. The 700-MHz spectrometer was purchased with the assistance of a converging technologies grant from the Israel Science Foundation .


  • KcsA potassium channel
  • biomolecular NMR
  • peptide oligomerization
  • sedimentation equilibrium
  • structural biology


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