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Basic Residues in the 74–83 and 191–198 Segments of Protein Kinase CK2 Catalytic Subunit are Implicated in Negative but not in Positive Regulation by the β‐Subunit
Author(s) -
Sarno Stefania,
Vaglio Philippe,
Marin Oriano,
Meggio Flavio,
Issinger OlafGeorg,
Pinna Lorenzo A.
Publication year - 1997
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1997.00290.x
Subject(s) - protein subunit , mutant , casein kinase 2 , peptide , protein kinase a , biochemistry , threonine , biology , serine , phosphorylation , kinase , chemistry , mitogen activated protein kinase kinase , gene
Protein kinase CK2 is a ubiquitous pleiotropic serine/threonine protein kinase whose holoenzyme is comprised of two catalytic (α and/or α') and two non‐catalytic, β‐subunits. The β‐subunit possesses antagonist functions that can be physically dissected by generating synthetic fragments encompassing its N‐terminal and C‐terminal domains. Here we show that by mutating basic residues in the 74‐77 and in the 191‐198 regions of the α‐subunit, the negative regulation by the β‐subunit and by its N‐terminal synthetic fragment CK2β‐(1–77), which is observable using calmodulin as a substrate for phosphorylation, is drastically reduced. In contrast, the positive regulation by a C‐terminal, CK2β‐(155–215)‐peptide is unaffected or even increased. Moreover, the basal activity of α mutants K74–77A, K79R80K83A, and R191R195K198A toward specific peptide substrates is stimulated by the β‐subunit many fold more than that of α wild type, while extrastimulation by β mutant D55L56E57A, observable with α wild type, is abolished with these mutants. These data support the conclusion that down regulation by the acidic residues clustered in the N‐terminal moiety of β is mediated by basic residues in the 74–83 and in the 191–198 sequences of the α‐subunit. These are also implicated in substrate recognition consistent with the concept that the N‐terminal acidic region of the β subunit operates as a pseudosubstrate. In contrast, another CK2α mutant, V66A, is more sensitive to inhibition by either β‐subunit or its N‐terminal, CK2β‐(1–77)‐peptide, while its stimulation by the C‐terminal peptide, CK2β‐(155–215), is comparable to that of α wild type. These observations suggest an indirect role of Val66 in conferring to the α‐subunit a conformation less sensitive to down regulation by β‐subunit.

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