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

Protein kinase CK2 is a heteromeric enzyme with catalytic (alpha) and regul atory (beta) subunits which form an alpha(2)beta(2) holoenzyme and utilizes both ATP and GTP as nucleotide substrate, Site-directed mutagenesis of CK2 alpha subunit was used to study this capacity to use GTP, Deletion of aspa ragine 118 (alpha(Delta N118)) or the mutant alpha N118E gives a 5-6-fold i ncrease in apparent K-m for GTP with little effect on the affinity for ATP. Mutants alpha N118A and alpha D120N did not alter significantly the K-m fo r either nucleotide, CK2 alpha(Delta N118) 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 CK2 alpha asparagine 118 in binding the guanine base. (C) 2000 Federation of Eu ropean Biochemical Societies.