Detailed state model of CaMKII activation and autophosphorylation

Abstract

By combining biochemical experiments with computer modelling of biochemical reactions we elucidated some of the currently unresolved aspects of calciumcalmodulin-dependent protein kinase II (CaMKII) activation and autophosphorylation that might be relevant for its physiological function and provided a model that incorporates in detail the mechanism of CaMKII activation and autophosphorylation at T286 that is based on experimentally determined binding constants and phosphorylation rates. To this end, we developed a detailed state model of CaMKII activation and autophosphorylation based on the currently available literature, and constrained it with data from CaMKII autophosphorylation essays. Our model takes exact phosphorylation patterns of CaMKII holoenzymes into account, and is valid at physiologically relevant conditions where the concentrations of calcium and calmodulin are not saturating. Our results strongly suggest that even when bound to less than fully calcium-bound calmodulin, CaMKII is in the active state, and indicate that the autophosphorylation of T286 by an active non-phosphorylated CaMKII subunit is significantly faster than by an autophosphorylated CaMKII subunit. These results imply that CaMKII can be efficiently activated at significantly lower calcium concentrations than previously thought, which may explain how CaMKII gets activated at calcium concentrations existing at synapses in vivo. We also investigated the significance of CaMKII holoenzyme structure on CaMKII autophosphorylation and obtained estimates of previously unknown binding constants.

Control of cell mechanics by RhoA and calcium fluxes during epithelial scattering

“…75,76 CaMKII subunits undergo cis-phosphorylation; pairing of subunit's catalytic domains allows for phosphorylation in trans, but this only occurs if both subunits are activated through Ca 2C /CaM binding. 74,[77][78][79] CaMKII has been implicated in EMT in development. 80 In xenopus development, CaMKII activation is seen in EMT and migration of fin core cells.…”

Structural studies on the regulation of Ca2+/calmodulin dependent protein kinase II

“…Simulation studies have shown that this phenomenon could be achieved without holoenzyme formation, if the various rate constants and concentrations are tuned appropriately (see, for example, [61,62]). An important role for the oligomeric structure is probably to bring the enzyme and substrate CaMKII into close proximity so that the rates of transphosphorylation and release of inhibition are matched appropriately to the Ca 2+ spike frequency.Importantly, the duration of each Ca 2+ pulse will affect the frequency threshold – a shorter pulse duration will necessitate a higher threshold frequency for activation and vice versa.…”

Regulation of gastrointestinal motility by Ca2+/calmodulin-stimulated protein kinase II

“…Following an increase in Ca 2+ , CaMKII is activated and autophosphorylated [55]. The holoenzyme kinase subunits are activated by Ca 2+ /CaM binding, resulting in phosphorylation of target substrates, and rapid intersubunit autophosphorylation of several sites [18,55].…”

“…The holoenzyme kinase subunits are activated by Ca 2+ /CaM binding, resulting in phosphorylation of target substrates, and rapid intersubunit autophosphorylation of several sites [18,55]. Autophosphorylation of Thr286 (numbering according to α isoform, Thr287 for β, γ and δ) by adjacent subunits disrupts the interaction of the autoinhibitory domain with the catalytic domain, and converts the holoenzyme into a Ca 2+ /CaM independent kinase (autonomous activity) that allows CaMKII to continue to phosphorylate its substrates after cytosolic Ca 2+ levels decrease [11,55]. In addition, the affinity of CaMKII for CaM increases about 1000-fold, a phenomenon termed ‘CaM trapping’ [56].…”