Screening for new inhibitors of human protein kinase CK2 by combining click chemistry and bacterial surface display

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

Abstract

The heterotetrameric serine/threonine kinase CK2 represents an emerging target in the treatment of neoplastic diseases [1]. The identification and characterization of new inhibitors of CK2 is a challenge, which requires innovative screening techniques and protein-protein interaction (PPI) analyses. 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 labeling strategy maintained CK2-functionality and phosphorylation activity contrary to commercially CK2-labeling through fluorescein isothiocyanate. The fluorescently labeled CK2 was used for bacterial surface display library screening to identify peptidic inhibitors by flow cytometry [3,4]. The inhibition of CK2 was determined by a capillary electrophoresis based activity assay. Furthermore, binding studies of specifically labeled CK2-subunits were performed using microscale thermophoresis. Consequently binding affinities of interaction partners/PPI‑inhibitors were characterized [4]. These techniques demonstrate that click chemistry and surface display are promising for drug discovery of human protein kinase CK2.