Structure and evolution of transplantation antigens: partial amino-acid sequences of H-2K and H-2D alloantigens.

Techniques for the amino acid sequence analysis of subnanomole quantities of polypeptides have been applied to characterize beta2-microglobulin and transplantation antigens of the mouse isolated from spleen cells by indirect immunoprecipitation. Eleven residues were identified throughout the NH2-terminal 27 residues of the beta2-microglobulin; all were identical to residues seen at the corresponding positions of beta2-microglobulins from other species. Two K and two D transplantation antigens were examined and the following generalizations emerged from the limited partial amino-acid sequence data: (1) the K and D molecules are homologous to one another; (2) they do not show amino acid sequence homology with immunoglobulins; (3) the two K and two D molecules differ from one another by multiple amino acid substitutions; and (4) the K molecules as a class cannot be distinguished from the D molecules as a class. The genetic and evolutionary implications of these observations are discussed.