Primary Structure of Pooled, Papain-solubilized HLA-A, -B, and -C Antigens

The tentative amino acid sequence of pooled, papain-solubilized HLA antigen heavy chains has been determined. The amino acid sequence comprises 273 residues. As the structural analyses were performed on HLA antigen heavy chains comprising a mixture of several allelic forms derived from the A, B, and possibly C loci, multiple residues were encountered in several positions. However, a quantitatively dominating residue could always be easily identified. The present data suggest that the amino acid variability of the HLA-A, -B, and -C antigens is found in restricted regions of the molecule. The COOH-terminal third of the HLA antigen heavy chain appears to be less variable than other regions of the molecule. Previous work has shown that the HLA antigen heavy chain contains two immunoglobulin-like disulphide loops. The COOH-terminal third of the heavy chain was shown to be similar in primary structure to β₂-microglobulin and the immunoglobulin G constant domains.