Complete amino acid sequence of the alpha 2 heavy chain of a human IgA2 immunoglobulin of the A2m (2) allotype.

The complete amino acid sequence of the alpha 2 heavy chain of a human IgA2 immunoglobulin of the A2m(2) allotype has been determined and is compared to the sequence of the alpha 1 chain of the human IgA1 subclass. The characteristic differences between the alpha 1 and alpha 2 chains are greatest in the hinge region and in the location and number of the oligosaccharides. Apart from the duplication in the hinge region of alpha 1 and the deletion in alpha 2, there are 23 amino acid exchanges in the constant (C) regions of the two chains. Accepted mutations are related to the surface accessibility of the residues and the proximity of carbohydrate. The results indicate that human IgA and IgG subclasses arose late in evolution and reflect similar mutationa pressures.