Structure of the heavy chain of the H-2Kk histocompatibility antigen.

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Abstract
Radiochemical techniques were used to characterize the H chain (Mr [molecular ratio] 46,000) of the murine H-2Kk histocompatibility antigen in terms of 6 fragments (I-VI) obtained after cleavage of the polypeptide chain with CNBr. The tentative order of the fragments, which account for more than 90% of the H chain, was assigned by radiochemical sequence analysis of the intact H chain and of each purified CNBr fragment and by analysis of the CNBr fragments obtained from the large papain fragment of the H chain. Treatment of cells with tunicamycin yielded H-2 molecules with H chains of MW 40,000, suggesting that the carbohydrate moieties have a combined MW of approximately 6000. CNBr cleavage of H-2Kk H chains labeled with [3H]fucose indicated that the carbohydrate moieties are located on fragments II and IV. Incubation of cells with 32PO4 gave H-2 molecules with radioactive phosphoserine in the carboxyl-terminal CNBr fragment (VI) of the H chain and in the fraction containing .beta.2-microglobulin. Sequence analysis of each CNBr fragment intrinsically labeled with 3H- and 35S-labeled amino acids identified 87 residues in the H-2Kk H chain. The sequence closely resembles that of the H-2Kb molecule, and the 11 differences are scattered througout the polypeptide chain. Comparison with HLA sequences indicates that the 2 allelic H-2 sequences are more closely related to each other (88% identity) than either is to the HLA-B7 or A2 antigens (.apprxeq. 70%). Similarly, the nonallelic HLA antigens are more closely related to each other (83%) than either is to the H-2Kk or H-2Kb molecules.