N-linked oligosaccharides of cobra venom factor contain novel α(1-3)galactosylated Lex structures

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 alpha1-3-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 H-1-NMR spectroscopy. Approximately 80% of the oligosaccharides are diantennary complex-type, similar to 12% are tri- and tetra-antennary complex-type, and similar to8% are oligomannose type structures. The majority of the complex-type oligosaccharides terminate in Gal alpha1-3Gal beta1-4(Fuc alpha1-3)GlcNAc beta1, a unique carbohydrate structural feature abundantly present in the glycoproteins of cobra venom.