Site-directed Mutants of the Beta Subunit of Protein Kinase CK2 Demonstrate the Important Role of Pro-58

The following amino acids of the Xenopus laevis beta subunit of protein kinase CK2 (casein kinase 2) were changed to alanine: Pro-58 (beta P-->A); Asp-59 and Glu-60 and Glu-61 (beta DEE-->AAA); His-151-153 (beta HHH-->AAA). The last 37 amino acids of the carboxyl end were deleted (beta delta 179-215). Stimulation of CK2 alpha catalytic subunit activity was measured with casein as substrate and the following relative activities were observed: beta P-->A > beta DEE-->AAA >>> beta WT > beta HHH-->AAA >>> beta delta 179-215. The beta DEE-->AAA and beta P-->A were similar to beta WT in reducing CD2 alpha binding to DNA but beta delta 179-215 was less active. The results indicate that both Pro-58 and the surrounding acidic cluster play roles in dampening the activation of CK2 alpha and that the carboxyl end of beta is involved in the interaction with CK2 alpha.