Characterization of protein kinase C theta activation loop autophosphorylation and the kinase domain catalytic mechanism.
Protein kinase C theta (PKCtheta), a member of the Ca(2+)-independent novel subfamily of PKCs, is required for T-cell receptor (TCR) signaling and IL2 production. PKCtheta-deficient mice have impaired Th2 responses in a murine ova-induced asthma model, while Th1 responses are normal. As an essential component of the TCR signaling complex, PKCtheta is a unique T-cell therapeutic target in the specific treatment of T-cell-mediated diseases. We report here the PKCtheta autophosphorylation characteristics and elucidation of the catalytic mechanism of the PKCtheta kinase domain using steady-state kinetics. Key phosphorylated residues of the active PKCtheta kinase domain expressed in Escherichia coli were characterized, and mutational analysis of the kinase domain was performed to establish the autophosphorylation and kinase activity relationships. Initial velocity, product inhibition, and dead-end inhibition studies provided assignments of the kinetic mechanism of PCKtheta(362)(-)(706) as ordered, wherein ATP binds kinase first and ADP is released last. Effects of solvent viscosity and ATPgammaS on PKCtheta catalysis demonstrated product release is partially rate limiting. Our studies provide important mechanistic insights into kinase activity and phosphorylation-mediated regulation of the novel PKC isoform, PKCtheta. These results should aid the design and discovery of PKCtheta antagonists as therapeutics for modulating T-cell-mediated immune and respiratory diseases.
Czerwinski
Robert
R
Department of Chemical and Screening Sciences, Wyeth Research, 87 Cambridge Park Drive, Cambridge, Massachusetts 02140, USA.
Aulabaugh
Ann
A
Greco
Rita M
RM
Olland
Stephane
S
Malakian
Karl
K
Wolfrom
Scott
S
Lin
Laura
L
Kriz
Ron
R
Stahl
Mark
M
Huang
Ying
Y
Liu
Lin
L
Chaudhary
Divya
D
D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002384:Catalysis; D020134:Catalytic Domain / Q000235:genetics; D004789:Enzyme Activation; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009994:Osmolar Concentration; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000074121:Protein Kinase C-theta; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000737:chemistry / Q000235:genetics; D013379:Substrate Specificity; D013912:Threonine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D007527:Isoenzymes; D010750:Phosphoproteins; D011994:Recombinant Proteins; D013912:Threonine; D012694:Serine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; C076233:PRKCQ protein, human; D011493:Protein Kinase C; D000074121:Protein Kinase C-theta