Powell L D, Sgroi D, Sjoberg E R, Stamenkovic I, Varki A
Glycobiology Program, University of California, La Jolla 92093-0063.
J Biol Chem. 1993 Apr 5;268(10):7019-27.
CD22 beta 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 CD22 beta 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 CD22 beta, [3H]glucosamine-labeled glycoproteins were purified from Daudi cells by adsorption onto a CD22 beta recombinant immunoglobulin (CD22 beta Rg) 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 CD22 beta Rg-PAS under the conditions used initially to adsorb the glycoproteins, but their elution from a column of CD22 beta Rg-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 alpha-2,3- and alpha-2,6-linked sialic acid in these different populations and their contribution to binding. Multiantennary oligosaccharides with one alpha-2,6-linked residue bound marginally, and those with two or more bound more tightly. alpha-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 beta-galactoside alpha-2,6 sialyltransferase and CMP-sialic acid. Thus, CD22 beta is a mammalian lectin that can recognize specific N-linked oligosaccharide structures containing alpha-2,6-linked sialic acids.
CD22β是一种在B细胞发育的特定阶段存在于其表面的糖蛋白。据信它在细胞间相互作用和B细胞激活中发挥作用。随附论文（Sgroi, D., Varki, A., Braesch-Andersen, S., and Stamenkovic, I. (1993) J. Biol. Chem. 268, 7011 - 7018）表明，CD22β识别T细胞和B细胞表面的多种糖蛋白，并且这些配体的唾液酸化对于结合至关重要。为了鉴定CD22β识别的唾液酸化寡糖的结构，通过吸附到连接在蛋白A - 琼脂糖（PAS）上的CD22β重组免疫球蛋白（CD22βRg）嵌合体上，从Daudi细胞中纯化[3H]葡萄糖胺标记的糖蛋白，然后用肽N - 糖苷酶F释放N - 连接寡糖。这些释放的寡糖在最初用于吸附糖蛋白的条件下未能与CD22βRg - PAS结合，但它们从CD22βRg - PAS柱上的洗脱明显延迟。具有不同亲和力的寡糖群体可以通过它们的洗脱顺序来鉴定。使用特定的唾液酸酶来确定这些不同群体中α - 2,3 - 和α - 2,6 - 连接的唾液酸含量及其对结合的贡献。带有一个α - 2,6 - 连接残基的多天线寡糖结合较弱，而带有两个或更多该残基的结合更紧密。α - 2,3 - 连接的唾液酸残基没有影响。结合不需要二价阳离子，并且唾液酸外侧链的温和高碘酸盐氧化会消除结合。在高亲和力和低亲和力寡糖群体之间未发现大小或岩藻糖含量的明显差异。然而，通过用β - 半乳糖苷α - 2,6唾液酸转移酶和CMP - 唾液酸处理，低亲和力群体可以部分转化为高亲和力群体。因此，CD22β是一种哺乳动物凝集素，能够识别含有α - 2,6 - 连接唾液酸的特定N - 连接寡糖结构。
