ISOLATION AND CHARACTERIZATION OF NOVEL MUCIN-LIKE GLYCOPROTEINS FROMCOBRA VENOM

A high molecular weight, heavily glycosylated protein fraction was iso lated from cobra venom. It consists of mucin-like glycoproteins (desig nated as cobra venom mucin) in noncovalent association with several lo wer molecular weight proteins and glycoproteins. The mucin was purifie d by CsBr density gradient centrifugation under dissociative condition s. The purified venom mucin comprised about 85% carbohydrate and 15% p rotein and was rich in Thr, Ser, Pro, Gly, Glu, Asp, and Ala. The muci n was resolved into two or more distinct classes of mucin-like glycopr oteins which differ in their amino acid compositions and/or carbohydra te content. Unlike other mucins, cobra venom mucin does not form highl y viscous solutions. It appears to keep several venom proteins and gly coproteins soluble by noncovalent interactions. Cobra venom mucin cont ains both O- and N-linked oligosaccharides; 1 N-linked chain for every 8-10 O-linked oligosaccharides. The O-linked chains are novel structu res with high molar proportions of fucose, galactose, and N-acetylgluc osamine relative to N-acetyl-galactosamine; they have a very low siali c acid content and lack sulfate esters. The majority of the O-linked o ligosaccharides are unusually large and contain 15 to as many as 50 su gar residues. The O-linked oligosaccharides are poly-N-acetyllactosami nyl chains consisting of -3Gal beta 1-4GlcNAc beta 1- and -3Gal beta 1 -4(Fuc alpha 1-3)GlcNAc beta 1-repeats and thus they contain inner Le( X) antigenic determinants. These oligosaccharides terminate with novel alpha-galactosylated Le(X) and Le(a) epitopes. Due to the abundance o f terminal alpha-galactosyl residues, cobra venom mucin reacts with an ti-alpha-Gal antibodies that are normally present in human serum.