Human CK2 is a heterotetrameric constitutively active serine / threonine protein kinase and plays an important role in current cancer research [1]. The kinase is composed of two catalytic CK2α subunits and two regulatory CK2β subunits. Most protein-protein interaction (PPI) studies or screening assays are based on fluorescence detection and require the labeling of the target enzyme by a fluorophore. Unfortunately, through labeling by commercial applications the catalytic subunit CK2α loses activity. Furthermore, the labeling ratio of the protein sample differs and is not exactly reproducible.

The solution for this problem was a bioorthogonal click reaction of the protein kinase. By expanding the genetic code, the unnatural amino acid para‑acidophenylalanine (pAzF) could be incorporated into CK2 [2]. Performing the SPAAC click reaction (Strain-Promoted Alkyne-Azide Cycloaddition) by the use of DBCO 545 (dibenzylcyclooctyne‑fluor 545) led to a specifically labeled human protein kinase CK2 [3].

This site specific labeling does not impair the phosphorylation activity of the kinase, which was evaluated by capillary electrophoresis. The innovatively labeled kinase in combination with the Autodisplay technology could be a significant advancement for inhibitor screening assays by flow cytometry and for CK2α/CK2β interaction studies [4].

References:

1. Trembley, J.H. et al.: Biofactors 2010, 36(3): 187-95.
2. Chin, J.W. et al.: J. Am. Chem. Soc. 2002, 124(31): 9026-7.
3. Mbua, N.E. et al.: Chembiochem. 2011, 12(12): 1912-21.
4. Jose, J., Meyer, T.F.: Microbiol. Mol. Biol. Rev. 2007, 71(4): 600-19.