Binding of Polyamines to an Autonomous Domain of the Regulatory Subunit of Protein Kinase CK2 Induces a Conformational Change in the Holoenzyme

Abstract

The means by which the cell regulates protein kinase CK2 remain obscure. However, natural polyamines, cellular compounds required for cell proliferation, have been reported to strongly stimulate CK2-mediated phosphorylation of a number of substrates. Using spermine analogs, we have shown that polyamines directly interact with the CK2 beta subunit, and the chemical features of the highly acidic binding site (Asp51-Tyr80) have been determined. In the present study, we show that the isolated beta subunit region extending from residue Asp51 to Pro110 exhibits a specific and efficient polyamine binding activity similar to that of the entire beta subunit. Moreover, the replacement of Glu60, Glu61, and Glu63 of the beta subunit by 3 alanine residues leads to a loss of the spermine-induced stimulation of CK2 activity which correlates with a decrease in spermine binding affinity. Thermal stability studies indicate that the binding of spermine induces a 4 degrees C decrease of the Tm value for the holoenzyme. This was confirmed by circular dichroism analyses, which show that the 6 degrees C negative shift of the CK2 Tm value provoked by spermine binding, reflects a conformational change in the kinase. Together, these observations strongly suggest that this newly defined polyamine-binding domain is involved in the intrasteric regulation of CK2 activity.