Cobra venom factor (CVF), a nontoxic, complement-activating glycoprotein in cobra venom, is a functional analog of mammalian complement component C3b. The carbohydrate moiety of CVF consists exclusively of N-linked oligosaccharides with terminal α1-3-linked galactosyl residues, which are antigenic in human. CVF has potential for several medical applications, including targeted cell killing and complement depletion. Here, we report a detailed structural analysis of the oligosaccharides of CVF. The structures of the oligosaccharides were determined by lectin affinity chromatography, antibody affinity blotting, compositional and methylation analyses, and high-resolution 1H-NMR spectroscopy. Approximately 80% of the oligosaccharides are diantennary complex-type, Ο12% are tri- and tetra-antennary complex-type, and Ο8% are oligomannose type structures. The majority of the complex-type oligosaccharides terminate in Galα1-3Galβ1-4(Fucα1-3)GlcNAcβ1, a unique carbohydrate structural feature abundantly present in the glycoproteins of cobra venom.
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