The Role of the N-Terminal Domain in the Regulation of the "Constitutively Active" Conformation of Protein Kinase CK2 alpha: Insight from a Molecular Dynamics Investigation

Protein kinase CK2 is an extremely well-conserved pleiotropic protein kinase with a growing list of substrates, the majority of which are proteins implicated in signal transduction, gene expression, and transcription-related functions. Protein kinase CK2 is a ubiquitous heterotetrameric serine/threonine protein kinase made up of two α or α' catalytic subunits and two β regulatory subunits. Moreover, protein kinase CK2 is defined as a "constitutively active" protein kinase in contrast to most other protein kinases characterized by the presence of distinct conformations associated with the active and inactive states. As previously demonstrated by in vitro mutation studies, CK2 activity is substantially regulated by the interaction between the N-terminal tail and the kinase domain. In fact, progressive deletions of the N-terminal tail show a decrease in the activity of the kinase. Even if the detrimental effects of Δ2-12 deletion can be partially reversed by the addition of a CK2β subunit, deletions Δ2-12 and Δ2-30 progressively decrease the basal activity of CK2. In particular, as experimentally demonstrated, the Δ2-12 N-terminal deletion affects both the K(M) value for ATP and for the substrate peptide, and the k(cat) value of CK2α. In this work, molecular dynamics (MD) simulations were carried out on wild-type (wt), Δ2-12 and Δ2-30 deletion mutants of CK2α in order to explore the role of the N-terminal tail on the conformational behavior of CK2. Furthermore, classical MD simulations were carried out to assess the anticipated impact of conformational changes in a novel set of CK2α mutant forms, such as the triple mutant Y206F-R10A-Y261F and the single mutant Y125F.