Glycobiology of immunoglobulin G

尽管类风湿关节炎患者血清IgG的Asn297连接糖链中的半乳糖缺乏已被证实，但糖链的结构分析尚不容易。绒毛拟青霉凝集素(PVL)优先与N-乙酰氨基葡萄糖β1*2man基团相互作用，建立了一种检测无乳糖lgG糖链末端的方法。血清lgG的PVL结合率与缺乏半乳糖的lgG的百分率显著相关。与年龄相关的PVL结合率略有增加。与配对血清样品相比，滑液中的PVL结合量显著增加。该检测系统可为检测无乳糖lgG提供一种理想的工具。三种LGG抗体上的N-连接糖链的结构，除了引入糖加成部位所需的改变外，在氨基酸序列上相同，这三种抗体都是葡聚糖特异的，但它们结合抗原的能力不同。除了Fc部分的糖基化位点外，每个抗体在重链的第二互补决定区(CDR2)有一个不同的糖基化位点。Asn54和Asn58的可变区糖酸盐结构是复合型的，而Asn60的可变区糖酸盐结构是高甘露糖结构。这些结果表明，重链可变区CDR2中碳水化合物结合位置的轻微变化可以显著改变糖的加工过程，同一多肽链中的复合型碳水化合物可能具有不同的结构。这些糖类结构的变化可以对重组抗体的生物学性质和潜在用途产生重大影响。

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.