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Publication Abstract from PubMed

The catalytic subunit of cAMP-dependent protein kinase (PKA) is a member of the AGC subfamily of protein kinases. While 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 Thr197 we used a PKA mutant which does not autophosphorylate at Thr197. The enzyme crystallized in the apo-state and the structure was solved to 3.0 angstroms. The N-lobe is rotated by 18 degrees 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.

Structural basis for the regulation of protein kinase A by activation loop phosphorylation.,Steichen JM, Kuchinskas M, Keshwani MM, Yang J, Adams JA, Taylor SS J Biol Chem. 2012 Feb 10. PMID:22334660^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.