Mouse Lyt-2 antigen: evidence for two heterodimers with a common subunit.

Abstract

Immunoprecipitation of [35S]methionine-labeled extracts of BALB/c thymocytes with mouse Lyt-2.2 monoclonal antibody yielded 3 components with subunit MW of 37,000, 32,000 and 28,000 on sodium dodecyl sulfate/polyacrylamide gel [SDS-PAGE] in the presence of a reducing agent. Two-dimensional polyacrylamide gel analysis revealed that, in the absence of a reducing agent, the 3 polypeptide chains exist in the form of 2 heterodimers, each consisting of 1 molecule of a MW 28,000 subunit covalently associated through disulfide bonds with either 1 MW 37,000 subunit or 1 MW 32,000 subunit. These 2 molecular structures are present in about equimolar ratios in the immunoprecipitate. Immunoautoradiographic analysis after electrophoretic transfer of proteins from a SDS-PAGE to a nitrocellulose membrane indicated that the Lyt-2.2 determinant detected by the monoclonal antibody resides on the MW 28,000 component, the common subunit of both heterodimeric structures. Lyt-2 precipitated from extracts of different T-cell growth factor-dependent cloned T-cell lines also showed similar structures, although the exact apparent MW of the respective components varied somewhat. The structure of the Lyt-2 antigen is of importance, particularly in the light of recent suggestions that it may be involved in the construction of 1 class of T-cell receptors.