Site-directed mutants of the β subunit of protein kinase CK2 demonstrate the important role of Pro-58

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Abstract
The following amino acids of the Xenopus laevis β subunit of protein kinase CK2 (casein kinase 2) were changed to alanine: Pro-58 ( β P→A ); Asp-59 and Glu-60 and Glu-61 ( β DEE→AAA ); His-151–153 ( β HHH→AAA ). The last 37 amino acids of the carboxyl end were deleted ( β Δ 179–215 ). Stimulation of CK2α catalytic subunit activity was measured with casein as substrate and the following relative activities were observed: β P→A > β DEE→AAA ⪢ β WT > β HHH→AAA ⪢ β Δ 179–215 . The β DEE→AAA and β P→A were similar to β WT in reducing CK2α binding to DNA but β Δ 179–215 was less active. The results indicate that both Pro-58 and the surrounding acidic cluster play roles in dampening the activation of CK2α and that the carboxyl end of β is involved in the interaction with CK2α.