Isolation, characterization and amino acid sequence studies of the cyanogen bromide fragments of the H‐2 Dd glycoprotein

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Abstract
The papain‐solubilized fragment of the H‐2Dd antigen, representing the NH2‐terminal 80% of the native glycoprotein, can be fragmented into five polypeptides using CNBr cleavage. These fragments have been isolated, characterized and subjected to amino acid sequence analysis using radiochemical microtechniques. It was possible to align these CNBr fragments by comparison of their NH2‐terminal amino acid sequence with the known amino acid sequence of the H‐2 Kb molecule. Thus, the NH2‐terminal fragment, D, contains 23 residues and is followed by a glycopeptide, fragment C, of 75 residues. Following fragment C are three fragments held together by disulfide bonds: fragment b 4, which has 40 amino acid residues, a second glycopeptide, fragment b 2, of 90 residues, and fragment b 3, a peptide of approximately 55 residues which terminates at the site of papain cleavage. The complete amino acid sequence of the NH2‐terminal CNBr fragment, D, has been determined, and this is presented here along with sequence data for the NH2‐terminal 30 residues of each of the other four CNBr fragments of the papain fragment of H‐2Dd. A total of 146 positions have been examined in the approximately 280‐residue H‐2D molecule, and a total of 127 residues have been positively determined. Most of the unassigned positions may be tentatively assigned as Asp or Asn, the only amino acids so far not incorporated in radiolabeled form by our metabolic labeling procedures into the H‐2 Dd molecule. Comparison of the sequence data obtained for the H‐2 Dd molecule to data available for other histocompatibility antigens revealed homologies of approximately 90% with H‐2 Kb and H‐2 Ld, and approximately 75% with HLA‐B 7 and HLA‐A2.