Phosphotyrosine as a specificity determinant for casein kinase-2, a growth related Ser/Thr-specific protein kinase

Abstract

The motif Ser-Ser-Ser-Glu-Glu is readily phosphorylated by casein kinase-2 (CK-2), a growth-related protein kinase whose consensus sequence is Ser(Thr)-Xaa-Xaa-Glu(Asp) [(1990) Biochim. Biophys. Acta. 1054, 267-283]. Here we show that phosphotyrosine can replace carboxylic acids as specificity determinant for CK-2 phosphorylation, the phosphotyrosyl peptide Ser-Ser-Ser-TyrP-TyrP actually being a substrate more efficient than Ser-Ser-Ser-Glu-Glu itself both in terms of Km (0.69 vs 2.43 mM) and V???. Prior dephosphorylation of phosphotyrosine entirely prevents the subsequent phosphorylation of serine by CK-2. While Ser-Ser-Ser-TyrP-TyrP is better than Ser-Ser-Ser-SerP-SerP, which in turn is be..