Coloma M J, Trinh R K, Martinez A R, Morrison S L
Department of Microbiology, Immunology, and Molecular Genetics, The Molecular Biology Institute, University of California, Los Angeles 90095, USA.
J Immunol. 1999 Feb 15;162(4):2162-70.
IgG is a glycoprotein with an N-linked carbohydrate structure attached to the CH2 domain of each of its heavy chains. In addition, the variable regions of IgG often contain potential N-linked carbohydrate addition sequences that frequently result in the attachment of V region carbohydrate. Nonetheless, the precise role of this V region glycan remains unclear. Studies from our laboratory have shown that a naturally occurring somatic mutant of an anti-dextran Ab that results in a carbohydrate addition site at Asn58 of the VH has carbohydrate in the complementarity-determining region 2 (CDR2) of the VH, and the presence of carbohydrate leads to an increase in affinity. However, carbohydrate attached to nearby positions within CDR2 had variable affects on affinity. In the present work we have extended these studies by adding carbohydrate addition sites close to or within all the CDRs of the same anti-dextran Ab. We find that carbohydrate is attached to all the novel addition sites, but the extent of glycosylation varies with the position of the site. In addition, we find that the position of the variable region carbohydrate influences some functional properties of the Ab, including those usually associated with the V region such as affinity for Ag as well as other characteristics typically attributed to the Fc such as half-life and organ targeting. These studies suggest that modification of variable region glycosylation provides an alternate strategy for manipulating the functional attributes of the Ab molecule and may shed light on how changes in carbohydrate structure affect protein conformation.
免疫球蛋白G（IgG）是一种糖蛋白，其每条重链的CH2结构域都连接有一个N-连接的碳水化合物结构。此外，IgG的可变区通常含有潜在的N-连接碳水化合物添加序列，这些序列常常导致可变区碳水化合物的附着。然而，这种可变区聚糖的确切作用仍不清楚。我们实验室的研究表明，一种抗右旋糖酐抗体的天然体细胞突变体在重链可变区（VH）的天冬酰胺58位产生了一个碳水化合物添加位点，该位点在VH的互补决定区2（CDR2）中有碳水化合物，并且碳水化合物的存在导致亲和力增加。然而，附着在CDR2内附近位置的碳水化合物对亲和力有不同的影响。在本研究中，我们通过在同一抗右旋糖酐抗体的所有互补决定区附近或内部添加碳水化合物添加位点，扩展了这些研究。我们发现碳水化合物附着在所有新的添加位点上，但糖基化程度随位点位置而变化。此外，我们发现可变区碳水化合物的位置会影响抗体的一些功能特性，包括那些通常与可变区相关的特性，如对抗原的亲和力，以及其他通常归因于Fc的特性，如半衰期和器官靶向性。这些研究表明，可变区糖基化的修饰为操纵抗体分子的功能属性提供了一种替代策略，并且可能有助于揭示碳水化合物结构的变化如何影响蛋白质构象。
