Natural ligands of the B cell adhesion molecule CD22β carry N-linked oligosaccharides with α-2,6-linked sialic acids that are required for recognition

Leland D. Powell, Dennis Sgroi, Eric R. Sjoberg, Ivan Stamenkovic, Ajit Varki

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218 Scopus citations

Abstract

CD22β is a glycoprotein found on the surface of B cells during restricted stages of development. It is believed to play a role in cell-cell interactions and B cell activation. The accompanying paper (Sgroi, D., Varki, A., Braesch-Andersen, S., and Stamenkovic, I. (1993) J. Biol. Chem. 268, 7011-7018) shows that CD22β recognizes multiple glycoproteins on the surfaces of T and B cells and that sialylation of these ligands is essential for binding. To identify the structure(s) of the sialylated oligosaccharide(s) recognized by CD22β, [3H]glucosamine-labeled glycoproteins were purified from Daudi cells by adsorption onto a CD22β recombinant immunoglobulin (CD22βRg) chimera attached to protein A-Sepharose (PAS), and the N-linked oligosaccharides were released by peptide N-glycosidase F. These released oligosaccharides failed to bind to CD22βRg-PAS under the conditions used initially to adsorb the glycoproteins, but their elution from a column of CD22βRg-PAS was significantly retarded. Populations of oligosaccharides with different affinities could be identified by their order of elution. Specific sialidases were used to determine the content of α-2,3- and α-2,6-linked sialic acid in these different populations and their contribution to binding. Multiantennary oligosaccharides with one α-2,6-linked residue bound marginally, and those with two or more bound more tightly. α-2,3-Linked sialic acid residues were without effect. Binding did not require divalent cations and was abrogated by mild periodate oxidation of the outer side chain of sialic acid. No marked differences in size or fucose content were found between the populations of high and low affinity oligosaccharides. However, the low affinity population could be partially converted into higher affinity by treatment with β-galactoside α-2,6 sialyltransferase and CMP-sialic acid. Thus, CD22β is a mammalian lectin that can recognize specific N-linked oligosaccharide structures containing α-2,6-linked sialic acids.

Original languageEnglish
Pages (from-to)7019-7027
Number of pages9
JournalJournal of Biological Chemistry
Volume268
Issue number10
StatePublished - 5 Apr 1993
Externally publishedYes

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