title: Structural basis for the regulation of protein kinase A by activation loop phosphorylation.
abstract: The catalytic subunit of cAMP-dependent protein kinase (PKA) is a member of the AGC group of protein kinases. Whereas PKA has served as a structural model for the protein kinase superfamily, all previous structures of the catalytic subunit contain a phosphorylated activation loop. To understand the structural effects of activation loop phosphorylation at Thr-197 we used a PKA mutant that does not autophosphorylate at Thr-197. The enzyme crystallized in the apo-state, and the structure was solved to 3.0 Å. The N-lobe is rotated by 18° relative to the wild-type apoenzyme, which illustrates that the enzyme likely exists in a wide range of conformations in solution due to the uncoupling of the N- and C-lobes. Several regions of the protein including the activation loop are disordered in the structure, and there are alternate main chain conformations for the magnesium positioning loop and catalytic loop causing a complete loss of hydrogen bonding between these two active site structural elements. These alterations are reflected in a 20-fold decrease in the apparent phosphoryl transfer rate as measured by pre-steady-state kinetic methods.
authors.affiliation: Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California 92093, USA.
authors.forename: Jon M
authors.initials: JM
authors.lastname: Steichen
authors.forename: Michael
authors.initials: M
authors.lastname: Kuchinskas
authors.forename: Malik M
authors.initials: MM
authors.lastname: Keshwani
authors.forename: Jie
authors.initials: J
authors.lastname: Yang
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Adams
authors.forename: Susan S
authors.initials: SS
authors.lastname: Taylor
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D051379:Mice; D008958:Models, Molecular; D020125:Mutation, Missense; D010766:Phosphorylation / Q000235:genetics; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
chemical_list: D017868:Cyclic AMP-Dependent Protein Kinases