Département de chimie moléculaire

X-ray crystallog. studies, as well as live-cell fluorescent imaging, have recently challenged the traditional view of protein kinase CK2. Unbalanced expression of catalytic and regulatory CK2 subunits has been obsd. in a variety of tissues and tumors. Thus the potential intersubunit flexibility suggested by these studies raises the likely prospect that the CK2 holoenzyme complex is subject to disassembly and reassembly. In the present paper, we show evidence for the reversible multimeric organization of the CK2 holoenzyme complex in vitro. We used a combination of site-directed mutagenesis, binding expts. and functional assays to show that, both in vitro and in vivo, only a small set of primary hydrophobic residues of CK2$\beta$ which contacts at the center of the CK2$\alpha$/CK2$\beta$ interface dominates affinity. The results indicate that a double mutation in CK2$\beta$ of amino acids Tyr188 and Phe190, which are complementary and fill up a hydrophobic pocket of CK2$\alpha$, is the most disruptive to CK2$\alpha$ binding both in vitro and in living cells. Further characterization of hotspots in a cluster of hydrophobic amino acids centered around Tyr188-Phe190 led us to the structure-based design of small-peptide inhibitors. One conformationally constrained 11-mer peptide (Pc) represents a unique CK2$\beta$-based small mol. that was particularly efficient (I) to antagonize the interaction between the CK2 subunits, (II) to inhibit the assembly of the CK2 holoenzyme complex, and (III) to strongly affect its substrate preference. [on SciFinder(R)]