RESUMEN
The study of cell-surface receptor dynamics is critical for understanding how cells sense and respond to changing environments. Therefore, elucidating the mechanisms by which signals are perceived and communicated into the cell is necessary to understand immunity, development, and stress. Challenges in testing interactions of membrane-bound proteins include their dynamic nature, their abundance, and the complex dual environment (lipid/soluble) in which they reside. Co-Immunoprecipitation (Co-IP) of tagged membrane proteins is a widely used approach to test protein-protein interaction in vivo. In this protocol we present a method to perform Co-IP using enriched membrane proteins in isolated microsomal fractions. The different variations of this protocol are highlighted, including recommendations and troubleshooting guides in order to optimize its application. This Co-IP protocol has been developed to test the interaction of receptor-like kinases, their interacting partners, and peptide ligands in stable Arabidopsis thaliana lines, but can be modified to test interactions in transiently expressed proteins in tobacco, and potentially in other plant models, or scaled for large-scale protein-protein interactions at the membrane.