PMID:8455615
| Citation |
Steinberg, RA, Cauthron, RD, Symcox, MM and Shuntoh, H (1993) Autoactivation of catalytic (C alpha) subunit of cyclic AMP-dependent protein kinase by phosphorylation of threonine 197. Mol. Cell. Biol. 13:2332-41 |
|---|---|
| Abstract |
We recently found, using cultured mouse cell systems, that newly synthesized catalytic (C) subunits of cyclic AMP-dependent protein kinase undergo a posttranslational modification that reduces their electrophoretic mobilities in sodium dodecyl sulfate (SDS)-polyacrylamide gels and activates them for binding to a Sepharose-conjugated inhibitor peptide. Using an Escherichia coli expression system, we now show that recombinant murine C alpha subunit undergoes a similar modification and that the modification results in a large increase in protein kinase activity. Threonine phosphorylation appears to be responsible for both the enzymatic activation and the electrophoretic mobility shift. The phosphothreonine-deficient form of C subunit had reduced affinities for the ATP analogs p-fluorosulfonyl-[14C]benzoyl 5'-adenosine and adenosine 5'-O-(3-thiotriphosphate) as well as for the Sepharose-conjugated inhibitor peptide; it also had markedly elevated Kms for both ATP and peptide substrates. Autophosphorylation of C-subunit preparations enriched for this phosphothreonine-deficient form reproduced the changes in enzyme activity and SDS-gel mobility that occur in intact cells. A mutant form of the recombinant C subunit with Ala substituted for Thr-197 (the only C-subunit threonine residue known to be phosphorylated in mammalian cells) was similar in SDS-polyacrylamide gel electrophoresis mobility and activity to the phosphothreonine-deficient form of wild-type C subunit. In contrast to the wild-type subunit, however, the Ala-197 mutant form could not be shifted or activated by incubation with the phosphothreonine-containing wild-type form. We conclude that posttranslational autophosphorylation of Thr-197 is a critical step in intracellular expression of active C subunit. |
| Links | |
| Keywords |
Adenosine Triphosphate/metabolism; Amino Acid Sequence; Animals; Electrophoresis, Polyacrylamide Gel; Enzyme Activation; Kinetics; Mice; Molecular Sequence Data; Peptides/metabolism; Phosphorylation; Phosphothreonine/chemistry; Protein Kinases/metabolism; Protein Processing, Post-Translational; Recombinant Proteins/metabolism; Substrate Specificity |
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