Complete amino acid sequence of pooled papain-solubilized HLA-A, -B, and -C antigens: relatedness to immunoglobulins and internal homologies.

Pooled, papain-solubilized HLA-A, -B, and -C antigens, derived from a large number of individuals and comprising several allelic forms, have been subjected to amino acid sequence determination. Despite the heterogeneity of the material, a main sequence representing all of the 273 amino acid residues could be established. The primary structure encompasses two immunoglobulin-like disulfide loops. The single carbohydrate moiety is attached to asparagine-86. Computer analyses demonstrated that the COOH-terminal one-third of the sequence, called H3, display statistically significant homology with members of the immunoglobulin family. The NH2-terminal two-thirds of the molecule, called H1 and H2, are not significantly homologous to any of the immunoglobulin sequences. However, H1 and H2 exhibit a distant relatedness to each other but no obvious similarity to the H3 region.