Location and structural significance of the oligosaccharides in human Ig-A1 and IgA2 immunoglobulins.

Abstract

The location, number and kinds of oligosaccharides in human Ig[immunoglobulin]A1 and IgA2 immunoglobulins were determined by amino acid sequence analysis of the .alpha. heavy chains. Both A2m allotypes of the .alpha.2 chain of IgA2 have 2 GlcN oligosaccharides that are absent in the .alpha.1 chain, but they lack GalN. The A2m(2) allotype has a 5th GlcN oligosaccharide. The .alpha. chains of IgA proteins also have subclass-specific and allotype-specific differences in amino acid sequence. Although other classes of human immunoglobulins differ in the number and kind of oligosaccharides, the sites are often homologous and are related to the immunoglobulin domain structure. Evolutionary preservation of the tripeptide acceptor sequence for GlcN probably indicates a structural and biological role for carbohydrate.