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Differential binding to phospholipid bilayers modulates membrane-damaging activity of Naja naja atra cardiotoxins

Pei-Hsiu Kao1, Shinne-Ren Lin, Long-Sen Chang

  • 1Institute of Biomedical Sciences, National Sun Yat-Sen University-Kaohsiung Medical University Joint Research Center, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.

Toxicon : Official Journal of the International Society on Toxinology
|May 20, 2009
PubMed

Insights

Naja naja atra cardiotoxins (CTXs) exhibit varying membrane-damaging activities based on their conformation and interaction with lipid bilayers. Loop II integrity is crucial for vesicle leakage, influencing toxin potency.

Area of Science:

  • Biochemistry
  • Toxicology
  • Membrane Biophysics

Background:

  • Cardiotoxins (CTXs) from Naja naja atra are known for their membrane-damaging effects.
  • Understanding the molecular mechanisms modulating CTX activity is crucial for toxin research.

Purpose of the Study:

  • To investigate the factors influencing the membrane-damaging activity of Naja naja atra cardiotoxins (CTXs).
  • To elucidate the role of CTX isotoxin conformation, binding, and orientation in vesicle permeabilization and hemolysis.

Main Methods:

  • Utilized liposomes composed of egg yolk phosphatidylcholine (EYPC) with dimyristoyl phosphatidic acid (DMPA) or egg yolk sphingomyelin (EYSM).
  • Assessed toxin-lipid interactions using fluorescence enhancement of labeled phospholipids and polydiacetylene membrane assays.
  • Investigated the role of specific amino acid residues (Met) and loop II integrity via chemical modification.
  • Measured hemolysis of cholesterol-depleted erythrocytes.

Main Results:

  • CTX isotoxins displayed differential activities in inducing vesicle leakage, despite similar binding affinities.
  • Topographical contact and membrane absorption patterns varied among CTX isotoxins.
  • Oxidation of Met residues in loop II affected vesicle leakage, with an intact loop II being critical for EYSM vesicle disruption.
  • CTXs induced significant hemolysis in cholesterol-depleted erythrocytes.

Conclusions:

  • Membrane-bound conformation and insertion mode of CTXs are key determinants of their membrane-damaging potency.
  • Lipid composition and membrane organization significantly influence CTX activity.
  • The structural integrity of loop II plays a differential role in disrupting various types of lipid vesicles.

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