Autophosphorylation of carboxy-terminal residues inhibits the activity of protein kinase CK1alpha.
CK1 constitutes a protein kinase subfamily that is involved in many important physiological processes. However, there is limited knowledge about mechanisms that regulate their activity. Isoforms CK1delta and CK1epsilon were previously shown to autophosphorylate carboxy-terminal sites, a process which effectively inhibits their catalytic activity. Mass spectrometry of CK1alpha and splice variant CK1alphaL has identified the autophosphorylation of the last four carboxyl-end serines and threonines and also for CK1alphaS, the same four residues plus threonine-327 and serine-332 of the S insert. Autophosphorylation occurs while the recombinant proteins are expressed in Escherichia coli. Mutation of four carboxy-terminal phosphorylation sites of CK1alpha to alanine demonstrates that these residues are the principal but not unique sites of autophosphorylation. Treatment of autophosphorylated CK1alpha and CK1alphaS with lambda phosphatase causes an activation of 80-100% and 300%, respectively. Similar treatment fails to stimulate the CK1alpha mutants lacking autophosphorylation sites. Incubation of dephosphorylated enzymes with ATP to allow renewed autophosphorylation causes significant inhibition of CK1alpha and CK1alphaS. The substrate for these studies was a synthetic canonical peptide for CK1 (RRKDLHDDEEDEAMS*ITA). The stimulation of activity seen upon dephosphorylation of CK1alpha and CK1alphaS was also observed using the known CK1 protein substrates DARPP-32, beta-catenin, and CK2beta, which have different CK1 recognition sequences. Autophosphorylation effects on CK1alpha activity are not due to changes in Km(app) for ATP or for peptide substrate but rather to the catalytic efficiency per pmol of enzyme. This work demonstrates that CK1alpha and its splice variants can be regulated by their autophosphorylation status.
Budini
Mauricio
M
Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Independencia 1027, Independencia 8380453 Santiago, Chile.
Jacob
Germaine
G
Jedlicki
Ana
A
Pérez
Carolina
C
Allende
Catherine C
CC
Allende
Jorge E
JE
D000595:Amino Acid Sequence; D000818:Animals; D055162:Biocatalysis; D048128:Casein Kinase Ialpha / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D013997:Time Factors; D015027:Zebrafish / Q000235:genetics / Q000378:metabolism
D021122:Protein Subunits; D048128:Casein Kinase Ialpha