Amino Acid Sequence Homology between HLA-A,B,C Antigens, beta2-Microglobulin and Immunoglobulins

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Abstract
Papain-solubilized HLA-A,B,C antigen [Ag] H chains were cleaved by combined acid and CNBr treatment to yield 3 large fragments. A 14,000-dalton peptide comprises the NH2-terminal portion of the molecule, less a 5-membered peptide. The 14,000-dalton fragment is followed in the linear sequence by a 9000-dalton peptide connected through an aspartyl-prolyl bond to the COOH-terminal 11,000-dalton fragment. The 9000- and 11,000-dalton fragments contain disulphide bridges that are immunoglobulin[Ig]-like; they encompass 55-60 amino acid residues. The NH2-terminal portion of the HLA Ag H chain is devoid of cysteine. NH2-terminal amino acid sequence analyses do not reveal homologies between the 14,000- and 9000-dalton fragments, .beta.2-microglobulin, and the constant Ig domains. The NH2-terminal sequence of the 11,000-dalton fragment is as homologous to .beta.2-microglobulin and the constant Ig domains as they are to one another.