Conformational Dynamics of Calmodulin in Complex with the Calmodulin-Dependent Kinase Kinase α Calmodulin-Binding Domain

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Abstract
As the primary intracellular calcium sensor, calcium-saturated calmodulin (CaM) regulates numerous and diverse proteins. Several mechanisms, including tissue-specific expression, localization, and sequestration, work in concert to limit the total number of available targets of calmodulin within a cell. While the free energies of binding of calmodulin-binding domains of regulated proteins by CaM have been shown to be highly similar, they result from vastly different enthalpic and entropic contributions. Here, we report the backbone and side-chain methyl dynamics of calcium-activated calmodulin in complex with a peptide corresponding to the CaM-binding domain of calmodulin kinase kinase, along with the thermodynamic underpinnings of complex formation. The results show a considerable reduction in side-chain mobility throughout CaM upon binding the CaMKKα peptide, which is consistent with the enthalpically driven nature of the binding. Site-specific comparison to another kinase-derived peptide complex with similar thermodynamic values reveals significant differences in dynamics largely localized to the hydrophobic binding sites.
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