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 glycoprotein CD45 were released as tritium‐labeled oligosaccharides by β‐elimination in the presence of NaB3H4. Mono Q column chromatography revealed that they comprise neutral (64 %) and acidic (36 %) oligosaccharides, the latter of which were converted to neutral ones by Arthrobacter ureafaciens sialidase treatment. Structural studies of each oligosaccharide fractionated on a Bio‐Gel P‐4 column by sequential exoglycosidase digestion and by methylation analysis revealed that human leukocyte CD45 contains mainly core 1 and core 2 oligosaccharides, 15 % of which are modified with poly (N‐acetyllactosamine) chains in different extensions. CD45 consists of several isoforms which were isolated after cell surface sialic acid residues were labeled by periodate/NaB3H4 treatment. Bio‐Gel P‐6 column chromatography of a mixture of the tritium‐labeled glycopeptide/oligosaccharides obtained by pronase‐digestion followed by mild alkaline borohydride treatment showed that distribution of the sialylated core 2 oligosaccharides is different among CD45 isoforms.