Quantitative Model of Calcium/Calmodulin- Dependent Protein Kinase II Activation

Citation

Mihalas, Stefan (2006) Quantitative Model of Calcium/Calmodulin- Dependent Protein Kinase II Activation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/d0zv-g984. https://resolver.caltech.edu/CaltechETD:etd-06052006-142955

Abstract

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a key element in the calcium second messenger cascades that lead to long term potentiation (LTP) of synaptic strength. In this thesis, I have constructed kinetic models of activation of CaMKII and measured some of the unknown parameters of the model. I used the models to elucidate mechanisms of activation of CaMKII and to study the kinetics of its activation under conditions similar to those in dendritic spines.

In chapter 2, I developed a new experimental method to rapidly stop the autophosphorylation reaction. I used this method to measure the catalytic turnover number of CaMKII. To quantitatively characterize CaMKII atophosphorylation in nonsaturating calcium, I also measured the autophosphorylation turnover number when CaMKII is activated by calmodulin mutants that can bind calcium ions only in either the amino or the carboxyl lobes.

Previous models of CaMKII activation assumed that binding of calmodulins to individual CaMKII subunits is independent and that autophosphorylation occurs within a ring of 6 subunits. However, a recent structure of CaMKII suggests that pairs of subunits cooperate in binding calmodulin and raises the possibility that the autophosphorylation occurs within pairs of subunits. In chapter 3, I constructed a model in which CaMKII subunits cooperate in binding calmodulin. This model reconciled previous experimental results from the literature that appeared contradictory. In chapter 4, I constructed two models for CaMKII autophosphorylation, in which autophosphorylation can occur either in rings or pairs, and used them to design experiments aimed at differentiating between these possibilities. Previously published measurements and the measurements that I performed are more consistent with autophosphorylation occurring within pairs.

In chapter 5, I constructed a model for simultaneous interactions among calcium, calmodulin, and CaMKII, and I used an automatic parameter search algorithm to fit the parameters for this model. I used it to characterize which of the parameters of calcium transients are critical for CaMKII activation.

This modeling work is part of a continuing effort to realistically model the spatial and temporal aspects of calcium second messenger signaling in dendritic spines.

Thesis Files