Many eukaryotic protein kinases are activated by phosphorylation on a specific conserved residue in the regulatory activation loop, a post-translational modification thought to stabilize the active DFG-In state of the catalytic domain. Here we use a battery of spectroscopic methods that track different catalytic elements of the kinase domain to show that the ~100 fold activation of the mitotic kinase Aurora A (AurA) by phosphorylation occurs without a population shift from the DFG-Out to the DFG-In state, and that the activation loop of the activated kinase remains highly dynamic. Instead, molecular dynamics simulations and electron paramagnetic resonance experiments show that phosphorylation triggers a switch within the DFG-In subpopulation from an autoinhibited DFG-In substate to an active DFG-In substate, leading to catalytic activation. This mechanism raises new questions about the functional role of the DFG-Out state in protein kinases.
Bibliographical noteFunding Information:
We thank LeeAnn Higgins and Todd Markowski (Center for Mass Spectrometry and Proteomics, University of Minnesota) and Joseph Dalluge (Mass Spectrometry Laboratory, University of Minnesota) for help with mass spectrometry experiments. DEER experiments were performed in the Biophysical Technology Center, University of Minnesota. We thank Tanya Freedman for critical reading of the manuscript, and Wendy Gordon for helpful discussions. This work was supported by NIH grants GM102288, CA217695 (NML), F32GM120817 (EFR) and P30-CA008748 and GM121505 (JDC). JDC, JMB, SMH, and SKA acknowledge support from the Sloan Kettering Institute.
© Ruff et al.