A novel allosteric site in casein kinase 2α discovered using combining bioinformatics and biochemistry methods

Casein kinase 2 (CK2) is a highly pleiotropic serine-threonine kinase, which catalyzed phosphorylation of more than 300 proteins that are implicated in regulation of many cellular functions, such as signal transduction, transcriptional control, apoptosis and the cell cycle. On the other hand, CK2 is abnormally elevated in a variety of tumors, and is considered as a promising therapeutic target. The currently available ATP-competitive CK2 inhibitors, however, lack selectivity, which has impeded their development in cancer therapy. Because allosteric inhibitors can avoid the shortcomings of conventional kinase inhibitors, this study was aimed to discover a new allosteric site in CK2 alpha and to investigate the effects of mutations in this site on the activity of CK2 alpha. Using Allosite based on protein dynamics and structural alignment, we predicted a new allosteric site that was partly located in the alpha C helix of CK2 alpha. Five residues exposed on the surface of this site were mutated to validate the prediction. Kinetic analyses were performed using a luminescent ADP detection assay by varying the concentrations of a peptide substrate, and the results showed that the mutations 1780 and 178W decreased CK2 alpha activity, whereas V31R, K75E, 1820 and P1090 increased CK2 alpha activity. Potential allosteric pathways were identified using the Monte Carlo path generation approach, and the results of these predicted allosteric pathways were consistent with the mutation analysis. Multiple sequence alignments of CK2 alpha with the other kinases in the family were conducted using the ClustaIX method, which revealed the diversity of the residues in the site. In conclusion, we identified a new allosteric site in CK2 alpha that can be altered to modulate the activity of the kinase. Because of the high diversity of the residues in the site, the site can be targeted using rational drug design of specific CK2 alpha inhibitors for biological relevance.