Direct quantification of cell type-specific proteins using Luminex assays with TurboID-labeled cells and tissues.

Cell type-specific proteome labeling provides enhanced understanding of cellular function and structure within tissues by tagging proteins during translation, while cells and tissues are in their "native" states. TurboID is a methodology to enable rapid and efficient biotinylation of proteins. New TurboID viral constructs and a Cre-mediated TurboID transgenic mouse line enable cell type-specific proteomic investigations in cell culture and in vivo settings. Together, these new tools enable diverse studies designed to interrogate individual cell type contributions within complex multi-cellular systems. While biotin-based labeling enables enrichment of the labeled proteome via immunoprecipitation, it is also compatible with biotin/streptavidin-based immunoassays, including the Luminex xMAP multiplexed immunoassay platform. Here, we detail protocols to utilize existing commercially available Luminex kits to directly detect TurboID-biotinylated (and therefore cell type-specific) proteins of interest from cell culture and bulk tissue samples. Luminex immunoassays have multiple advantages compared to other methodologies, including (1) requiring small sample volumes/masses, (2) direct immuno-reaction-based quantification from a target sample without intermediate processing steps, (3) reduced costs and (4) direct readout. Below, we describe an adapted Luminex xMAP protocol to quantify phospho-proteins and cytokines from TurboID-labeled cells or tissues with cell type-specificity.