Physical interactions driving the activation/inhibition of calcium/calmodulin dependent protein kinase II.

CaMKII is a protein kinase whose function is regulated by the binding of the Calcium/Calmodulin complex (Ca/CaM). It is a major player in the Long Term Potentiation process where it acts as a molecular switch, oscillating between inhibited and active conformations. The mechanism for the switching is thought to be initiated by Ca/CaM binding, which allows the trans-phosphorylation of a subunit of CaMKII by a neighboring kinase, leading to the active state of the system. A combination of all-atom and coarse-grained MD simulations with free energy calculations, led us to reveal an interplay of electrostatic forces exerted by Ca/CaM on CaMKII, which initiate the activation process. The highly electrically charged Ca/CaM neutralizes basic regions in the linker domain of CaMKII, facilitating its opening and consequent activation. The emerging picture of CaMKII's behavior highlights the preponderance of electrostatic interactions, which are modulated by the presence of Ca/CaM and the phosphorylation of key sites.