Allosteric Regulation of Protein Kinase Enzymes via an Electrostatic Switch that Modulates Active Site Dynamics

Protein kinase (PK) enzymes are a large family of signaling proteins that play a central role in signal transduction pathways. Robust regulation of their catalytic activity is critical, and many oncogenes harbor mutations that result in misregulated PK activity. The chemical basis for how some PK regulatory factors ultimately affect the rate of chemistry is still not completely understood. We have identified a long-range electrostatic switch that we believe is used by allosteric PK regulatory factors to modulate the rate of chemistry by tuning active-site dynamics.We applied a combination of crystallography, kinetics, and molecular dynamics to determine the chemical kinetic basis for how this electrostatic switch, toggled by regulatory subunit binding, affects each step of catalysis by CDK2 kinase. We engineered point mutants to deconstruct the kinetic, dynamic, and thermodynamic consequences of the switch. We also evaluated other PKs and find that, although it has evolved to be triggered in different ways by diverse PK regulatory factors, the mechanics of this switch can be conserved.We demonstrate that a key component of the switch is that it affects a significant change in the electrostatic potential within the ATP∗Mg binding site of the enzyme. This electrostatic effect is propagated through the low-dielectric protein interior and directly affects the two dominant rate-determining steps of catalysis: attenuating both the recruitment of catalytically essential Mg cofactors (affecting both kcat and KM) as well as the release of the ADP product.Conclusion: We present a chemical hypothesis that provides a mechanistic explanation for one way that a large-scale conformation transition, observed in diverse PK family members, is able to significantly affect the rate of chemistry by acting at a distance from the active site.