title: (RP)-cAMPS inhibits the cAMP-dependent protein kinase by blocking the cAMP-induced conformational transition.
abstract: (RP)-cAMPS is known to inhibit competitively the cAMP-induced activation of cAMP-dependent protein kinase (PKA). The molecular nature of this inhibition, however, is unknown. By monitoring the intrinsic tryptophan fluorescence of recombinant type I regulatory subunit of PKA under unfolding conditions, a free energy value (delta GDH2O) of 8.23 +/- 0.22 kcal/mol was calculated. The cAMP-free form of the regulatory subunit was less stable with delta GDH2O = 6.04 +/- 0.05 kcal/mol. Native stability was recovered by treatment of the cAMP-free protein with either cAMP or (SP)-cAMPS but not with (RP)-cAMPS. Thus, (RP)-cAMPS binding to the regulatory subunit keeps the protein in a locked conformation, unable to release the catalytic subunit. This finding was further supported by demonstrating that holoenzyme formation was greatly accelerated only when bound cAMP was replaced with (RP)-cAMPS but not with cAMP or (SP)-cAMPS.
mesh_terms: D001120:Arginine; D001665:Binding Sites; D002151:Calorimetry; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007700:Kinetics; D008239:Lysine; D046911:Macromolecular Substances; D017354:Point Mutation; D011487:Protein Conformation / Q000187:drug effects*; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D013873:Thionucleotides / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D013873:Thionucleotides; C016957:adenosine-3',5'-cyclic phosphorothioate; D001120:Arginine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D008239:Lysine