2.2 Å refined crystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with MnATP and a peptide inhibitor

. The crystal structure of a ternary complex containing the catalytic subunit of cAMP-dependent protein kinase, ATP and a 20-residue inhibitor peptide was refined at a resolution of 2.2 Å to an R value of 0.177. In order to identify the metal binding sites, the crystals, originally grown in the presence of low concentrations of Mg²⁺, were soaked in Mn²⁺. Two Mn²⁺ ions were identified using an anomalous Fourier map. One Mn²⁺ ion bridges the γ- and β-phosphates and interacts with Asp184 and two water molecules. The second Mn²⁺ ion interacts with the side chains of Asn171 and Asp l84 as well as with a water molecule. Modeling a serine into the P site of the inhibitor peptide suggests a mechanism for phosphotransfer.