Involvement of asparagine 118 in the nucleotide specificity of the catalytic subunit of protein kinase CK2

Abstract

Protein kinase CK2 is a heteromeric enzyme with catalytic (α) and regulatory (β) subunits which form an α2β2 holoenzyme and utilizes both ATP and GTP as nucleotide substrate. Site-directed mutagenesis of CK2α subunit was used to study this capacity to use GTP. Deletion of asparagine 118 (α(ΔN118)) or the mutant αN118E gives a 5-6-fold increase in apparent K(m) for GTP with little effect on the affinity for ATP. Mutants αN118A and αD120N did not alter significantly the K(m) for either nucleotide. CK2α(ΔN118) has an apparent K(i) for inosine 5' triphosphate 5-fold higher than wild-type and is very heat labile. These studies complement recent crystallographic data indicating a role for CK2α asparagine 118 in binding the guanine base. (C) 2000 Federation of European Biochemical Societies.