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Ion channels formed in planar lipid bilayers by the dipteran-specific Cry4B Bacillus thuringiensis toxin and its

Theeraporn Puntheeranurak1, Panapat Uawithya, Léna Potvin

  • 1Laboratory of Molecular Biophysics, Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom 73170, Thailand.

Molecular Membrane Biology
|December 12, 2003
PubMed

Insights

Bacillus thuringiensis (Bt) Cry4B toxin and its N-terminal fragment form cation-selective ion channels. This study confirms the alpha1-alpha5 region

Area of Science:

  • Molecular Biology
  • Biophysics
  • Insect Toxicology

Background:

  • Bacillus thuringiensis (Bt) Cry4B is a 130-kDa protein activated by trypsin into a 65-kDa toxin targeting mosquito larvae.
  • The active toxin comprises 45-kDa and 20-kDa protease-resistant products.
  • A 21-kDa N-terminal fragment of Cry4B permeabilizes liposomes, suggesting potential ion channel activity.

Purpose of the Study:

  • To investigate if Cry4B functions as a channel-forming toxin in planar lipid bilayers.
  • To determine if the 21-kDa N-terminal fragment (alpha1-alpha5 region) is sufficient for ion channel activity.

Main Methods:

  • Circular dichroism spectroscopy to analyze the secondary structure of the 21-kDa fragment.
  • Planar lipid bilayer experiments to measure ion channel formation and properties.
  • Electrophysiological recordings to assess channel conductance and ion selectivity.

Main Results:

  • The 21-kDa polypeptide exhibits an alpha-helical structure.
  • Both full-length Cry4B and the alpha1-alpha5 fragment form cation-selective ion channels with distinct conductances (248 pS and 207 pS, respectively).
  • The alpha1-alpha5 fragment forms channels at lower doses, remaining open longer with flickering activity, suggesting regulatory differences.

Conclusions:

  • The alpha1-alpha5 N-terminal region of Cry4B is a functional ion channel former, similar to the full-length toxin.
  • This fragment alone can account for the ion channel activity of the Cry4B toxin.
  • A pH-dependent region may regulate the channel properties of Cry4B.

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