Glycobiology of immunoglobulin G

虽然类风湿关节炎患者血清IgG中Asn 297连接的糖链中的半乳糖缺陷已经被确定，但糖链的结构分析还不容易获得。绒毛小球藻凝集素（PVL）优先与N-乙酰葡糖胺β 1 * 2 Man基团相互作用，暴露在半乳糖IgG中糖链的末端。建立了一种检测血清半乳糖IgG的方法，血清IgG的PVL结合率与半乳糖缺陷型IgG的百分率呈显著相关，年龄-PVL结合率在滑液中显著高于配对血清样品，该测定系统可为检测agalcto IgG提供一种简单、灵敏的理想工具。已经确定了连接到三种IgG抗体上的连接糖链，除了引入碳水化合物添加位点所需的改变之外，三种抗体在氨基酸序列上是相同的。每个抗体在重链的第二互补决定区（CDR 2）中具有不同的糖基化位点。这些结果表明，在重链可变区的CDR 2内碳水化合物连接位置的轻微变化可以实质上改变碳水化合物加工，在同一多肽链中含有的复合型碳水化合物可以具有不同的结构，这些碳水化合物结构的改变可以对重组抗体的生物学特性和潜在的有用性产生显著的影响。

Although the galactose deficiency in the Asn297-linked sugar chains of serum lgG from patients with rheumatoid arthritis has been established, structural analysis of sugar chains has not readily available.Psathyrella velutina lectin (PVL) preferentially interacts with the N-acetylglucosaminebeta1*2Man group, exposed at the termini of sugar chains in agalacto lgG.An ELISA-based assay for the detection of agalacto lgG was developed.PVL binding of serum lgG signifilcantiy correlated with percentage of galactose-deficient lgG.Age-related slight increase in PVL binding was observed.PVL binding was significantly higher in the synovial fluid compared with paired serum samples.This assay system may provide an ideal tool for the simple and sensitive detection of agalcto lgG.The structure of the N-linked sugar chains attached to three lgG antibodies, identical in amino acid sequence except for the change required to introduce the carbohydrate addition sites, has been determined.All three antibodies are specific for dextran but differ in their ability to bind antigen.In addtition to the glycosylation site in the Fc portion, each antibody has a different glycosylation site in the second complementarity determining region (CDR2) of the heavy chain.The variable region carbohyrate structures attached at Asn54 and Asn58 were complex-type but that at Asn60 was a high mannose structure.These results demonstrate that slight changes in the position of carbohydrate attachment within CDR2 of the variable region of the heavy chain can substantially alter carbohydrate processing and that complex-type carbohydrates contained within the same polypeptide chain can have different structures.These alterations in carbohydrate structure can have significant consequences on the biological properties and potential usefulness of recombinant antibodies.