Src kinase dissected: conformational dynamics reveal how to hijack natural regulatory mechanisms

A necessity for cell survival is finely tuned signaling inputs and the propagation of those signals. Protein kinases that phosphorylate signaling proteins are known as the “writers” of these signals, whereas phosphatases are known as the “erasers.” The interplay between these two proteins is crucial for signal propagation. When these signals are not tightly regulated, they often lead to a wide variety of cancers. A commonly studied protein kinase family is the Src family kinases that are crucial to cell regulation and implicated in many types of cancer. Using a suite of biochemical and biophysical techniques, we show activation loop phosphorylation (activating) wins the tug of war over C-terminal tail phosphorylation (inactivating) by modulating the open and closed equilibrium. We uncover a novel mechanism of activation of Src kinase dependent on phosphorylation of the activation loop in the closed conformation. We show dephosphorylation of the inhibitory tyrosine by the protein tyrosine phosphatase SHP2 can only occur in the open state, and activation loop phosphorylation can drive dephosphorylation of the C-terminal tail through a