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Immunoreactivity and function of oligosaccharides in cobra venom factor
D C Gowda1, E C Petrella, T T Raj
1Department of Biochemistry and Molecular Biology, Georgetown University, Washington, DC 20007.
Journal of Immunology (Baltimore, Md. : 1950)
|March 15, 1994
Summary
Cobra venom factor (CVF) has unique sugar chains that bind human antibodies but are not essential for its complement-activating function. Modifying these chains does not affect CVF
Area of Science:
- Biochemistry
- Immunology
- Glycobiology
Background:
- Cobra venom factor (CVF) is a complement-activating glycoprotein and a functional analog of human complement component C3.
- CVF possesses a unique, novel carbohydrate structure: a symmetric fucosylated biantennary complex-type N-linked chain with an alpha-galactosylated Le(x) epitope.
- Naturally occurring anti-alpha-Gal antibodies in human serum bind to CVF.
Purpose of the Study:
- To investigate the impact of anti-alpha-Gal antibodies on CVF function.
- To determine the effect of oligosaccharide modification or removal on CVF activity and immunoreactivity.
- To assess the potential human applications of CVF by understanding its glycan interactions.
Main Methods:
- Chemical and enzymatic modifications of CVF oligosaccharides: de-alpha-galactosylation, deglycosylation, and sialylation.
- Functional assays: assessment of C3/C5 convertase formation with human factor B and human serum decomplementation.
- Structural analysis: far UV circular dichroism to evaluate changes in secondary structure.
- Immunoreactivity testing with anti-alpha-Gal antibodies.
Main Results:
- De-alpha-galactosylation and deglycosylation abolished immunoreactivity with anti-alpha-Gal antibodies.
- Modified CVF (de-alpha-galactosylated and deglycosylated) retained full C3/C5 convertase activity and human serum decomplementation capacity.
- Oligosaccharide removal slightly decreased thermal stability but minimally affected secondary structure.
- Enzymatically sialylated CVF showed unchanged secondary structure and activity compared to native CVF.
Conclusions:
- The complex oligosaccharide chains of CVF are not essential for its complement-activating function.
- CVF's glycan structure is responsible for its binding to human anti-alpha-Gal antibodies.
- Modifications to CVF's oligosaccharides, including sialylation, do not impair its functional activity, suggesting potential for therapeutic applications.