Allosteric Inhibitors of Human Protein Kinase CK2: Identification by Click Chemistry and Bacterial Surface Display

Nienberg C, Garmann C, Bollacke A, Saenger T, Gratz A, Jose J

Abstract

CK2 is a heterotetrameric constitutively active serine/threonine protein kinase and represents anemerging target in the treatment of neoplastic diseases [1]. Central aspects for the identification andcharacterization of new inhibitors are screening- and protein-protein interaction (PPI) assays.In this study the unnatural amino acid para azidophenylalanine (pAzF) was incorporated in the CK2-subunits. By a SPAAC click reaction a site-specific labeling of CK2 was obtained [2]. This labelingstrategy maintained CK2-functionality and phosphorylation activity contrary to commercially CK2-labelingby fluorescein isothiocyanate. By Autodisplay [3] the fluorescently labeled CK2 could be used forbacterial surface display library screening. Thereby a potent allosteric peptidic inhibitor, called B2, wasidentified. B2 inhibited the CK2 holoenzyme as well as the CK2α subunit with an IC50 value of 0.8 μMand was neither ATP- nor substrate competitive [4]. Furthermore, binding studies of specifically labeledCK2 and interaction partners/ PPI-inhibitors were performed by microscale thermophoresis. Unknownbinding affinities were clarified and the KD value of CK2α and B2 was determined to be 2.16 μM [4].These results demonstrate that the combination of click chemistry and surface display is promising fordrug discovery of human protein kinase CK2.