Investigation of Activity and Nucleotide Binding of Vaccinia-related Kinase 3 (VRK3)
Kinases play important roles in the regulation of mitosis and cell signaling. Overexpression and misregulation of many kinases can lead to disease, and kinases have made highly successful drug targets for the treatment of cancer. The vaccinia-related kinase (VRK) family are serine/threonine kinases which have higher levels of expression in cells that are actively dividing. Two members of this family, VRK1 and VRK2, are functional kinases which play roles in the cell cycle, transcription regulation, and cell signaling. However, the third member of this family, VRK3, is classified as a pseudokinase, meaning it does not behave like most conserved kinases in the human kinome. It only weakly binds ATP due to substitutions in its sequence compared to VRK1 and VRK2. In this study, point mutations were made to the structure of the VRK3 kinase domain in an attempt to increase its activity. These point mutations were of the large hydrophobic residues thought to block VRK3’s binding site to residues conserved in VRK1 and VRK2. Mutant VRK3 kinase domains were then purified and stability was tested in vitro using circular dichroism. Nucleotide binding was tested using circular dichroism, and enzyme activity was quantified using a coupled kinase assay.