Sequence homology of the LFA-1 and Mac-1 leukocyte adhesion glycoproteins and unexpected relation to leukocyte interferon.
Cell-surface adherence reactions are fundamental to the biology of lymphocytes, monocytes and granulocytes. The lymphocyte function-associated 1 (LFA-1) and macrophage 1 (Mac-1) glycoproteins mediate differing types of adhesion reactions on these cells. LFA-1 participates in T-lymphocyte and natural killer-cell adhesion to target cells, whereas the Mac-1 antigen is identical to the complement receptor type 3, which mediates adhesion of monocytes and granulocytes to C3bi-sensitized particles. Deficiency of these proteins, in a heritable disease, results in multiple adhesion-related leukocyte defects. LFA-1 and Mac-1 resemble one another in overall structure, having alpha-subunits of relative molecular mass (Mr) 180,000 and 170,000, respectively, which are non-covalently associated with beta-subunits of Mr 95,000 in alpha 1 beta 1 complexes. Peptide mapping and immunological cross-reactivity have shown that the beta-subunits are highly related if not identical, but have revealed no similarities between the alpha-subunits. Nonetheless, the shared beta-subunit suggested that LFA-1 and Mac-1 might be members of a protein family containing diversified but evolutionarily related alpha-subunits. Therefore, we examine here the structure of the alpha-subunits by N-terminal amino-acid sequencing. Sequence homology shows that the alpha-subunits are members of a novel leukocyte adhesion protein family, and suggests that their evolution occurred by gene duplication. A search for similarities to previously sequenced proteins reveals a further unexpected homology between LFA-1 and leukocyte (alpha) interferons.
D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000276:immunology*; D002448:Cell Adhesion; D006801:Humans; D007370:Interferon Type I; D016169:Lymphocyte Function-Associated Antigen-1; D008214:Lymphocytes / Q000276:immunology; D016177:Macrophage-1 Antigen; D008264:Macrophages / Q000276:immunology; D051379:Mice; D051381:Rats
D000954:Antigens, Surface; D007370:Interferon Type I; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen