CaMKII binds both substrates and activators at the active site

Abstract

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a signaling protein required for long-term memory. When activated by Ca²⁺/CaM, it sustains activity even after the Ca²⁺ dissipates. In addition to the well-known autophosphorylation-mediated mechanism, interaction with specific binding partners also persistently activates CaMKII. A long-standing model invokes two distinct S and T sites. If an interactor binds at the T-site, then it will preclude autoinhibition and allow substrates to be phosphorylated at the S site. Here, we specifically test this model with X-ray crystallography, molecular dynamics simulations, and biochemistry. Our data are inconsistent with this model. Co-crystal structures of four different activators or substrates show that they all bind to a single continuous site across the kinase domain. We propose a mechanistic model where persistent CaMKII activity is facilitated by high-affinity binding partners that kinetically compete with autoinhibition by the regulatory segment to allow substrate phosphorylation.

Keywords: AMPA-type glutamate receptor; CP: Molecular biology; Ca(2+)/calmodulin dependent protein kinase II; LTP; NMDA-type glutamate receptor; Tiam1; X-ray crystallography.