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Related Experiment Videos

Ion selectivity of colicin E1: modulation by pH and membrane composition.

J O Bullock1

  • 1Department of Physiology, University of Missouri-Columbia 65212.

The Journal of Membrane Biology
|February 1, 1992
PubMed
Summary

Colicin E1 forms ion channels in lipid bilayers, with anion or cation selectivity influenced by pH. This selectivity is controlled by a pH-sensitive conformational change, particularly in phosphatidylcholine membranes, leading to irreversible states.

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Area of Science:

  • Biophysics
  • Molecular Biology
  • Membrane Protein Studies

Background:

  • Colicin E1, a bacterial protein, forms voltage-gated ion channels in lipid bilayers.
  • Channel properties, including ion selectivity, can be modulated by environmental factors like pH.

Purpose of the Study:

  • Investigate the pH-dependent ion selectivity of Colicin E1 channels in different lipid environments.
  • Determine the mechanism underlying pH-induced changes in Colicin E1 channel selectivity.

Main Methods:

  • Incorporation of Colicin E1 into planar lipid bilayers composed of asolectin, phosphatidylethanolamine, and diphytanoyl phosphatidylcholine.
  • Electrophysiological measurements to assess ion channel activity and selectivity under varying pH conditions.

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Main Results:

  • Colicin E1 channels exhibit pH-dependent anion or cation selectivity, which can be reversed by altering pH in asolectin and phosphatidylethanolamine bilayers.
  • In phosphatidylcholine membranes, exposure to low pH (4.0) on the cis side induces an irreversible state, rendering channels refractory to further pH changes.
  • Protonation of specific groups on the cis side appears crucial for the anion-selective state, with these groups becoming inaccessible in phosphatidylcholine membranes.

Conclusions:

  • Colicin E1 ion channel selectivity is regulated by pH-sensitive conformational changes.
  • The lipid environment, specifically phosphatidylcholine, influences the dynamics and reversibility of these pH-induced conformational transitions.