Mapping protein receptor-ligand interactions via in vivo chemical crosslinking, affinity purification, and...

Protein receptor-ligand interactions play important roles in mediating enzyme catalysis, signal transduction, and other protein functions. Immunoaffinity purification followed by mass spectrometry analysis is a common method for identifying protein receptor-ligand complexes. However, it is difficult to distinguish between specific protein binding partners and non-specifically bound proteins that co-purify with the complex. In addition, weakly interacting binding partners may dissociate from the protein receptor-ligand complexes during immunoaffinity purification. The combination of chemical crosslinking, affinity purification, and differential mass spectrometry analysis provides a direct method for capturing stable, weak, and transient protein interactions that occur in vivo and in vitro. This approach enables the identification of functional receptor-ligand binding partners with high confidence. Herein, we describe a differential mass spectrometry approach coupled with in situ chemical crosslinking and immunoaffinity purification for identifying receptor-ligand binding partners. In particular, we identified a functional, counter-ligand structure of the natural killer cell p30-related protein.