Abstract
Examination of interactions between a transmembrane protein and a soluble protein by pull-down or immunoprecipitation assays can be tricky and complicated due to the detergent extraction of membrane proteins during the lysate preparation step. The choice and concentration of detergents must be determined empirically and the procedure can be burdensome. Here, we describe a simplified binding assay by expressing the membrane protein of interest in COS-7 cells and applying detergent-free solutions containing an extracellular protein to be tested. The binding is then examined by immunocytochemistry.