The inhibition of TMCB toward the purified CK2 holoenzyme CK2α2β2 results in a Ki value of 10.1 nM. In addition, Ki values are determined with the surface displayed isoform CK2 holoenzymes and turned out to be of 31.1 nM for CK2α2β2 and 19.6 nM for CK2α'2β2. The surface display of CKα and CK2α', in the context of the corresponding holoenzymes, can be used to identify selective compounds.