BINDING OF POLYAMINES TO AN AUTONOMOUS DOMAIN OF THE REGULATORY SUBUNIT OF PROTEIN-KINASE CK2 INDUCES A CONFORMATIONAL CHANGE IN THE HOLOENZYME - A PROPOSED ROLE FOR THE KINASE STIMULATION

The means by which the cell regulates protein kinase CK2 remain obscur e, However, natural polyamines, cellular compounds required for cell p roliferation, have been reported to strongly stimulate CK2-mediated ph osphorylation of a number of substrates, Using spermine analogs, we ha ve shown that polyamines directly interact with the CK2 beta subunit, and the chemical features of the highly acidic binding site (Asp(51)-T yr(80)) have been determined, In the present study, we show that the i solated beta subunit region extending from residue Asp(51) to Pro(110) exhibits a specific and efficient polyamine binding activity similar to that of the entire beta subunit, Moreover, the replacement of Glu(6 0), Glu(61), and Glu(63) of the beta subunit by 3 alanine residues lea ds to a loss of the spermine-induced stimulation of CK2 activity which correlates with a decrease in spermine binding affinity, Thermal stab ility studies indicate that the binding of spermine induces a 4 degree s C decrease of the T-m value for the holoenzyme. This was confirmed b y circular dichroism analyses, which show that the 6 degrees C negativ e shift of the CK2 T-m value provoked by spermine binding, reflects a conformational change in the kinase. Together, these observations stro ngly suggest that this newly defined polyamine binding domain is invol ved in the intrasteric regulation of CK2 activity.