STRUCTURAL STUDY OF THE O-LINKED SUGAR CHAINS OF HUMAN-LEUKOCYTE TYROSINE PHOSPHATASE CD45

The O-linked sugar chains of the human leukocyte cell surface glycopro tein CD45 were released as tritium-labeled oligosaccharides by beta-el imination in the presence of (NaBH4)-H-3. Mono Q column chromatography revealed that they comprise neutral (64%) and acidic (36%) oligosacch arides, the latter of which were converted to neutral ones by Arthroba cter ureafaciens sialidase treatment. Structural studies of each oligo saccharide fractionated on a Bio-Gel P-4 column by sequential exoglyco sidase digestion and by methylation analysis revealed that human leuko cyte CD45 contains mainly core 1 and core 2 oligosaccharides, 15% of w hich are modified with poly (N-acetyllactosamine) chains in different extensions. CD45 consists of several isoforms which were isolated afte r cell surface sialic acid residues were labeled by periodate/(NaBH4)- H-3 treatment. Bio-Gel P-6 column chromatography of a mixture of the t ritium-labeled glycopeptide/oligosaccharides obtained by pronase-diges tion followed by mild alkaline borohydride treatment showed that distr ibution of the sialylated core 2 oligosaccharides is different among C D45 isoforms.