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Heparin and heparan sulfate bind to snake cardiotoxin. Sulfated oligosaccharides as a potential target for
H V Patel1, A A Vyas, K A Vyas
1Department of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan 30043, USA.
Abstract:
Cardiotoxins (CTXs) from cobra venom show cytotoxicity toward several cell types. They cause systolic heart arrest and severe tissue necrosis. Their interaction with phospholipids is established but by itself fails to explain the specificity of these toxins; other component(s) of membrane must, therefore, intervene to direct them toward their target. We herein show, for the first time, that sulfated glycosaminoglycans, heparin, heparan sulfate (HS), chondroitin sulfate (CS), and dermatan sulfate (DS), interact with CTX A3, a major component of Taiwan cobra venom, by use of affinity chromatography, circular dichroism, absorbance, and fluorescence intensity and anisotropy measurements. The relative strength of binding, determined by the NaCl concentration required to dissociate the CTX-glycosaminoglycan complex, varied as follows: heparin > DS > CS > HS. In physiological buffer (8 mM Na2HPO4, 2.7 mM KCl, 1.8 mM KH2PO4, 138 mM NaCl, pH 7.4), however, only heparin and HS bound to CTX, with respective dissociation constants of 1.4 and 16 microM, while CS and DS failed to exhibit well defined binding behavior, as indicated by fluorescence measurements. We estimate that CTX makes 3-4 ionic contacts with heparin based on a salt-dependent binding study and that approximately 40% of binding free energy is derived from purely electrostatic interactions under physiological conditions. Sulfated pentasaccharide may be sufficient to bind to CTX. We also found that heparin accentuates the penetration of CTX into phospholipid membranes as analyzed by Langmuir monolayer measurement. In view of these results we propose that heparin-like moieties of the cell surface may modulate the action of CTX.
Insights
Cobra cardiotoxins (CTXs) bind to sulfated glycosaminoglycans like heparin and heparan sulfate. This interaction, driven by electrostatic forces, may influence how CTXs affect cell membranes and cause tissue damage.
Area of Science:
- Biochemistry
- Toxicology
- Molecular Biology
Background:
- Cardiotoxins (CTXs) from cobra venom are cytotoxic, causing heart arrest and necrosis.
- CTX interaction with phospholipids is known but doesn't fully explain their target specificity.
- Cell surface components likely play a role in directing CTX activity.
Purpose of the Study:
- To investigate the interaction between CTX A3 and various sulfated glycosaminoglycans (GAGs).
- To determine the binding affinity and characteristics of CTX-GAG complexes.
- To explore the role of GAGs in modulating CTX membrane penetration and action.
Main Methods:
- Affinity chromatography was used to assess CTX A3 binding to heparin, heparan sulfate (HS), chondroitin sulfate (CS), and dermatan sulfate (DS).
- Circular dichroism, absorbance, and fluorescence spectroscopy measured binding constants and interactions.
- Langmuir monolayer measurements analyzed the effect of heparin on CTX membrane penetration.
Main Results:
- CTX A3 demonstrated varying binding affinities for GAGs, with relative strength: heparin > DS > CS > HS.
- Under physiological conditions, only heparin and HS showed significant binding to CTX A3 (dissociation constants 1.4 and 16 μM, respectively).
- Heparin enhanced CTX A3 penetration into phospholipid membranes, suggesting a role in modulating toxicity.
Conclusions:
- Sulfated glycosaminoglycans, particularly heparin and HS, interact with cobra cardiotoxin A3.
- Binding is primarily electrostatic, with heparin-like moieties potentially directing CTX action.
- These findings suggest cell surface GAGs modulate the cytotoxic effects of cobra cardiotoxins.