Rapid Evaluation of CK2 Enzymatic Activity and CK2α/CK2β- Interaction in recombinant E. coli Cell Lysates

Protein Kinase CK2 is a ubiquitous Serin/Threonine Kinase consisting of a catalytic alpha and a regulatory beta subunit. First described in 1954, CK2 is now recognized for its involvement in a variety of biological processes and known to regulate more than 10% of the phosphoproteome. This study introduces a novel, rapid assay to measure CK2α activity in Escherichia coli cell lysates. By fusing CK2α with the fluorescent protein mScarlet it was possible to quantify CK2α concentration directly in lysates. We used the dose-dependent increase of CK2α activity after addition of CK2β^1-193 to determine the dissociation constants (K_D) of the CK2α/CK2β-interaction. As a first trial, activity and affinity of the variant CK2α^R191Q to CK2β^1-193 was investigated using the developed assays. This mutation in the CSNK2A1 gene, encoding CK2α is related to the Okur-Chung Neurodevelopmental Syndrome (OCNDS). Apparent K_D values of 13 nM for the CK2α^R191Q/CK2β interaction and 7.4 nM for the CK2α/CK2β interaction were determined using nonlinear regression. Similarly to recent approaches, uncertainties with regards to the concentration of both binding partners were propagated through the entire process of nonlinear regression by Monte Carlo simulations. This way, accuracy confidence intervals of the K_D-values were derived. This resulted in 96.4 % confidence that the accurate K_D-values of the CK2α/CK2β and CK2α^R191Q/CK2β interactions were different. The results suggest potential disruptions in oligomeric assembly caused by the R191Q mutation.