An inactive mutant of the alpha subunit of protein kinase CK2 that traps the regulatory CK2 beta subunit

Protein kinase CK2 (casein kinase 2) is a ubiquitous Ser/Thr protein kinase involved in cell proliferation, Mutation of the alpha subunit of the Xenopus laevis CK2 to change aspartic acid 156 to alanine (CK2 alpha A(156)) resulted in an inactive enzyme, The CK2 alpha A(156) mutant, however, binds the regulatory subunit as measured by retention of beta on a nickel chelating column mediated by (His)(6)-tagged CK2 alpha A(156). Addition of CK2 alpha A(156) also caused beta to shift sedimentation in a sucrose gradient from a beta(2) dimer (52 kDa) to an alpha(2) beta(2) tetramer (130 000 kDa), CK2 alpha A(156) can trap the beta subunit in an inactive complex reducing the stimulation of casein phosphorylation caused by addition of beta to wild-type alpha. This competitive effect depends on the ratio of alpha/alpha A(156) and on the amount of beta available, Since beta inhibits the phosphorylation of calmodulin by CK2 alpha, the addition of CK2 alpha A(156), in this case, increases calmodulin phosphorylation by the alpha and beta combination, These results suggest that CK2 alpha A(156) may be a useful dominant-negative mutant that can serve to explore the multiple functions of CK2 beta. (C) 1997 Federation of European Biochemical Societies.