Analysis of the structure of the human T cell surface antigen T8 by limited proteolysis and chemical cleavage.

The structure of the human T lymphocyte surface antigen T8 (Leu 2) has been explored utilizing limited proteolysis on viable cells and cellular lysates. The positions of the cleavage sites of trypsin and papain were placed relative to the single CNBr cleavage point. Additional data allowed the location of the amino and carboxyl termini relative to the enzymatic and chemical cleavage sites. This information, together with earlier evidence concerning the position of a membrane binding site, allowed the construction of a model illustrating the vectorial orientation of the molecule on the cell. Within this model, the approximate positions of disulfide linkages were indicated based on the results of nonreduced/reduced two-dimensional sodium sulfide-polyacrylamide gel electrophoresis. Carbohydrate moieties were localized using cleavage with trifluoromethanesulfonic acid, a reagent which cleaves both N-linked and O-linked oligosaccharides. Finally, the implications of the proteolysis experiments in relation to the function of T8 were discussed.