Active site profiling reveals coupling between domains in SRC-family kinases

Src family kinase mutants, with altered regulatory domain interactions, were profiled with a photodependent crosslinking strategy to reveal conformation-specific ATP-competitive inhibitors that affect intermolecular binding interactions. Protein kinases, key regulators of intracellular signal transduction, have emerged as an important class of drug targets. Chemical proteomic tools that facilitate the functional interrogation of protein kinase active sites are powerful reagents for studying the regulation of this large enzyme family and performing inhibitor selectivity screens. Here we describe a new crosslinking strategy that enables rapid and quantitative profiling of protein kinase active sites in lysates and live cells. Applying this methodology to the SRC-family kinases (SFKs) SRC and HCK led to the identification of a series of conformation-specific, ATP-competitive inhibitors that have a distinct preference for the autoinhibited forms of these kinases. Furthermore, we show that ligands that have this selectivity are able to modulate the ability of the regulatory domains of SRC and HCK to engage in intermolecular binding interactions. These studies provide insight into the regulation of this important family of tyrosine kinases.