Structural studies of murine I-E and human DR antigens

The structures of murine I-E antigens from two strains of mice were compared to each other and to human DR antigens. Murine and human antigens were isolated by using allo- and xenoantiserum, respectively, and purified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The murine I-E and human DR antigens consist of two polypeptide chains designated α and β. The E α and DR α chains display a high degree of amino acid sequence homology as do the E β and DR β chains, provided a gap is inserted at position 1 of the DR β chain. Comparison of N-terminal sequences reveals several differences between the β chains of I-E antigens from the two strains of mice. In contrast no sequence differences between the two α chains are observed. In addition, comparison of tryptic peptides examined by isoelectrofocusing reveals several differences between the two E β chains, but not between the two E α chains. Thus, the polymorphism of murine I-E antigens and by analogy human DR antigens, may result from structural differences in the smaller (β) chain.