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Freeze-fracture study of cardiotoxin action on axonal membrane and axonal membrane lipid vesicles
Abstract:
Freeze-fracture electron microscopy was used to follow morphological changes induced by Naja mossambica mossambica venom cardiotoxins on crab axonal membranes and thier lipids. It was shown that the extent of morphological changes depended drastically on the purity of cardiotoxin preparations and on their nature. Highly purified cardiotoxin induced mainly fusion of membrane or lipid vesicles. The extent of fusion and other morphological changes depended on the nature of cardiotoxin used: VII4 cardiotoxin induced only fusion while VII1 led to further modifications of membranes and liposomes. The most spectacular morphological changes were observed with axonal membranes treated with cardiotoxin containing traces of venom phospholipase A2. At low cardiotoxin concentration (10(-7)-10(-5) M) important intramembrane particle aggregation was observed and at higher concentrations (more than 10(-4) M) intramembrane particles disappeared from the membrane and were found in solution. The membrane vesicles, devoid of intramembrane particles, were observed to fuse rapidly into liposome-like aggregates. These morphological changes are interpreted as being due to the removal of intrinsic membrane proteins from the membrane by the combined action of cardiotoxin and phospholipase A2.
Insights
Naja mossambica mossambica venom cardiotoxins alter crab axonal membranes. The extent of these morphological changes, including membrane fusion and particle aggregation, depends on cardiotoxin purity and the presence of phospholipase A2.
Area of Science:
- Biochemistry
- Cell Biology
- Neuroscience
Background:
- Cardiotoxins from Naja mossambica mossambica venom are known to affect cell membranes.
- Understanding their precise mechanisms of action on axonal membranes is crucial for neurobiology.
Purpose of the Study:
- To investigate the morphological changes induced by cardiotoxins on crab axonal membranes and lipids using freeze-fracture electron microscopy.
- To determine the influence of cardiotoxin purity and nature on these alterations.
- To elucidate the role of phospholipase A2 in conjunction with cardiotoxins.
Main Methods:
- Utilized freeze-fracture electron microscopy to visualize structural changes in crab axonal membranes.
- Examined the effects of varying concentrations and purities of cardiotoxin preparations.
- Assessed the impact of cardiotoxin combined with venom phospholipase A2.
Main Results:
- Highly purified cardiotoxins primarily induced fusion of membrane or lipid vesicles.
- Different cardiotoxin types (VII4 vs. VII1) exhibited distinct effects on membrane morphology.
- Cardiotoxin with phospholipase A2 caused significant intramembrane particle aggregation and subsequent disappearance, leading to fusion of particle-depleted vesicles.
Conclusions:
- Morphological changes are highly dependent on cardiotoxin purity and specific type.
- The combined action of cardiotoxin and phospholipase A2 leads to the removal of intrinsic membrane proteins, resulting in membrane fusion.
- These findings provide insights into the molecular interactions of snake venom components with neuronal membranes.