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Interactions between ?CaMKII and calmodulin in living cells: conformational changes arising from CaM-dependent and -independent relationships.

ABSTRACT:

Background

?CaMKII plays central and essential roles in long-term potentiation (LTP), learning and memory. ?CaMKII is activated via binding with Ca²?/CaM in response to elevated Ca²? concentration. Furthermore, prolonged increase in Ca²? concentration leads to the auto-phosphorylation of ?CaMKII at T286, maintaining the activation of ?CaMKII even after Ca²?/CaM dissociation. Importantly, the active form of ?CaMKII is thought to exhibit conformational change. In order to elucidate the relationships between the interaction of ?CaMKII with CaM and the conformational change of ?CaMKII, we generated molecular probes (YFP-?CaMKII with CFP-CaM and YFP-?CaMKII-CFP) and performed time-lapse imaging of the interaction with CaM and the conformational change, respectively, in living cells using FRET.

Results

The interaction of YFP-?CaMKII with CFP-CaM and the conformational change of YFP-?CaMKII-CFP were induced simultaneously in response to increased concentrations of Ca²?. Consistent with previous predictions, high levels of Ca²? signaling maintained the conformational change of YFP-?CaMKII-CFP at the time when CFP-CaM was released from YFP-?CaMKII. These observations indicated the transfer of ?CaMKII conformational change from CaM-dependence to CaM-independence. Furthermore, analyses using ?CaMKII mutants showed that phosphorylation at T286 and T305/306 played positive and negative roles, respectively, during in vivo interaction with CaM and further suggested that CaM-dependent and CaM-independent conformational changed forms displays similar but distinct structures.

Conclusions

Importantly, these structual differences between CaM-dependent and -independent forms of ?CaMKII may exhibit differential functions for ?CaMKII, such as interactions with other molecules required for LTP and memory. Our molecular probes could thus be used to identify therapeutic targets for cognitive disorders that are associated with the misregulation of ?CaMKII.

SUBMITTER: Kato K

PROVIDER: S-EPMC3765210 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Publications

Interactions between αCaMKII and calmodulin in living cells: conformational changes arising from CaM-dependent and -independent relationships.

Kato Ken-ichi K Iwamoto Taku T Kida Satoshi S

Molecular brain 20130819

<h4>Background</h4>αCaMKII plays central and essential roles in long-term potentiation (LTP), learning and memory. αCaMKII is activated via binding with Ca²⁺/CaM in response to elevated Ca²⁺ concentration. Furthermore, prolonged increase in Ca²⁺ concentration leads to the auto-phosphorylation of αCaMKII at T286, maintaining the activation of αCaMKII even after Ca²⁺/CaM dissociation. Importantly, the active form of αCaMKII is thought to exhibit conformational change. In order to elucidate the rel ...[more]

PMID: 23958294

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Project description:Calmodulin-dependent kinase II (CaMKII) has long been known to play an important role in learning and memory as well as long term potentiation (LTP). More recently it has been suggested that it might be involved in the time averaging of synaptic signals, which can then lead to the high precision of information stored at a single synapse. However, the role of the scaffolding molecule, neurogranin (Ng), in governing the dynamics of CaMKII is not yet fully understood. In this work, we adopt a rule-based modeling approach through the Monte Carlo method to study the effect of Ca2+ signals on the dynamics of CaMKII phosphorylation in the postsynaptic density (PSD). Calcium surges are observed in synaptic spines during an EPSP and back-propagating action potential due to the opening of NMDA receptors and voltage dependent calcium channels. Using agent-based models, we computationally investigate the dynamics of phosphorylation of CaMKII monomers and dodecameric holoenzymes. The scaffolding molecule, Ng, when present in significant concentration, limits the availability of free calmodulin (CaM), the protein which activates CaMKII in the presence of calcium. We show that Ng plays an important modulatory role in CaMKII phosphorylation following a surge of high calcium concentration. We find a non-intuitive dependence of this effect on CaM concentration that results from the different affinities of CaM for CaMKII depending on the number of calcium ions bound to the former. It has been shown previously that in the absence of phosphatase, CaMKII monomers integrate over Ca2+ signals of certain frequencies through autophosphorylation (Pepke et al, Plos Comp. Bio., 2010). We also study the effect of multiple calcium spikes on CaMKII holoenzyme autophosphorylation, and show that in the presence of phosphatase, CaMKII behaves as a leaky integrator of calcium signals, a result that has been recently observed in vivo. Our models predict that the parameters of this leaky integrator are finely tuned through the interactions of Ng, CaM, CaMKII, and PP1, providing a mechanism to precisely control the sensitivity of synapses to calcium signals. Author Summary not valid for PLOS ONE submissions.