The Enzyme Database

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Accepted name: cAMP-dependent protein kinase
Reaction: ATP + a [protein]-(L-serine/L-threonine) = ADP + a [protein]-(L-serine/L-threonine) phosphate
Glossary: 3′,5′-cyclic-AMP = cAMP
Other name(s): PKA; protein kinase A; PKA catalytic (C) subunit; A kinase; ATP:protein phosphotransferase (cAMP-dependent)
Systematic name: ATP:protein Ser/Thr-phosphotransferase (3′,5′-cAMP-dependent)
Comments: This eukaryotic enzyme recognizes the sequence -Arg-Arg-X-Ser*/Thr*-Hpo, where * indicates the phosphorylated residue and Hpo indicates a hydrophobic residue.The inactive holoenzyme is a heterotetramer composed of two regulatory (R) subunits and two catalytic (C) subunits. Each R subunit occludes the active site of a C subunit and contains two binding sites for 3′,5′-cyclic-AMP (cAMP). Binding of cAMP activates the enzyme by causing conformational changes that release two free monomeric C subunits from a dimer of the R subunits, i.e. R2C2 + 4 cAMP = R2(cAMP)4 + 2 C. Activity requires phosphorylation of a conserved Thr in the activation loop (T-loop) sequence (Thr198 in human Cα; Thr224 in budding yeast Tpk2), installed by auto-phosphorylation or by the 3-phosphoinositide-dependent protein kinase-1 (PDPK1). Certain R2C2 combinations can be localized to particular subcellular regions by their association with diverse species of 'A Kinase-Anchoring Proteins' (AKAPs). The enzyme has been characterized from many organisms. Humans have three C units (Cα, Cβ, and Cγ) encoded by the paralogous genes PRKACA, PRKACB and PRKACG, respectively, and four R subunits (R1α, RIβ, RIIα and RIIβ), encoded by PKRAR1A, PKRAR1B, PKRAR2A and PKRAR2B, respectively. Yeast (Saccharomyces cerevisiae) has three C subunits (Tpk1, Tpk2, and Tpk3) encoded by the paralogous genes TPK1, TPK2 and TPK3, respectively, and a single R subunit (Bcy1) encoded by the BCY1 gene. Some validated substrates of the enzyme include cAMP-response element-binding protein (CREB), phosphorylase kinase α subunit (PHKA), and tyrosine 3-monooxygenase (TH) in mammals; Adr1, Whi3, Nej1, and Pyk1 in yeast.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 142008-29-5
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