Structure and Role of Oligosaccharide on Antibody Light Chains and Their Modification with Glycosylation-based Cytotechnology

The immunoglobulin is a glycoprotein consisting of heavy and light chains on which the carbohydrate chains are located, normally in the heavy chain constant region. Although immunoglobulin light chains usually lack carbohydrates, some light chains contain carbohydrate chains in their variable region. In this mini review we will discuss the structure, role and modification of carbohydrates on immunoglobulin light chains. We have found an Af-glycosylated carbohydrate chain on the light chain-hypervariable region of a human monoclonal antibody which is reactive to lung adenocarcinoma and is produced by a human hybridoma. A carbohydrate chain linked to one of the light chain glycoforms is characterized as hybrid-type, which is rare for any immunoglobulin isotype. To clarify the role of carbohydrates in the light chain variable region, we attempted to modify the glycosylation on this particular light chain. Carbohydrate moiety changes on this light chain produced in concanavalin A-resistant hybridoma clones and the following treatment of these variant light chains with various glycosidases leads to an alteration in the antigen binding activity. To modify the antigen-binding activity of the antibody by altering glycosylation on the light chain, we examined the effects of varying availability of glucose and other monosaccharides in the culture medium. Appropriate N-glycosylation on the light chain, which leads to higher antigen-binding, can be accomplished by modulating monosaccharide availability in the culture medium. Cell clones lacking sensitivity to a glucose level change for light chain glycosylation were screened from the lectin-resistant variants to obtain clones which produce glycoforms reproducibly in various culture environments.