A One-Step Procedure for Biotinylation and Chemical Cross-Linking of Lymphocyte Surface and Intracellular Membrane-Associated Molecules

Abstract

The use of cell surface biotinylation has become a popular alternative to radioiodination in studies involving labeling of cell surface molecules. The possibility of using biotinylation and chemical cross-linking to label and covalently link associated molecules in T lymphocytes was explored using immunoprecipitation, SDS-PAGE analysis, and protein detection by enhanced chemiluminescence (ECL). Reduced and nonreduced SDS-PAGE analysis of CD45 and Thy-1 mAb immunoprecipitates from 1% Triton X-100 lysates of murine thymocytes surface biotinylated in the presence of the homobifunctional cross-linker DTSSP [3,3′-dithio-bis (sulfosuccinimidylpropionate), 0.2 mg/ml] revealed that the surface molecules CD45 and Thy-1 can be biotinylated and chemically linked, and is consistent with a previous report using cell surface radioiodination. Also, CD45 and CD3 mAb immunoprecipitates from 1% digitonin lysates of the murine T cell clone D10 and of the human leukemic T cell line Jurkat, biotinylated after permeabilization of the cells with lysolecithin (20-25 μg/ml), revealed several additional coprecipitating molecules of 16, 32, 34, 56, 60 and 80 kDa not detected in immunoprecipitates from lysates of surface-biotinylated cells. The failure to detect these molecules in lysates of surface-biotinylated cells suggests that these molecules biotinylate poorly by cell surface labeling, or are localized intracellularly. The intracellular localization of some of these molecules is supported by the fact that the 56-kDa molecule seen in CD45 mAb immunoprecipitates from lysates of Jurkat cells biotinylated in the presence of lysolecithin could be identified as the src-like tyrosine kinase p56 lck by immunoblotting with p56 lck Abs. The results show, therefore, that certain associated cell surface and intracellular proteins can be biotinylation and chemically linked using a single-step procedure. We expect that the technique will further broaden the use of biotinylation and nonradioactive protein detection, particularly in studies characterizing the molecular associations of cell surface receptors with other molecules, either on the cell surface or inside the cell.