EndoNB: A general strategy to study the internalization of cell surface proteins

The cell surface harbors thousands of distinct proteins whose function depend on continuous cycles of internalization and replenishment. Disturbances in this turnover are typical hallmarks of many diseases. Yet, tools to study the dynamics of most surface proteins are suboptimal or unavailable. Here, we present a new method that enables the analysis of surface protein turnover of virtually any surface protein at endogenous levels. Our approach combines CRISPR/cas9-mediated genome engineering with a cleavable recombinant probe, which addresses many of the shortcomings of current methodologies. We demonstrate the capabilities our method by studying the internalization behavior of a previously uncharacterized surface protein and by assessing the effect of ligands and activity modulators in the endocytic behavior of established receptors. In summary, our method represents a versatile strategy to explore surface protein biology and enhances our ability to study the mechanisms of membrane protein retrieval and recycling.