2.2-ANGSTROM 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 angstrom 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 gamma- and beta-phosphates and interacts with Asp184 and two water molecules. The second Mn2+ ion interacts with the side chains of Asn171 and Asp184 as well as with a water molecule. Modeling a serine into the P site of the inhibitor peptide suggests a mechanism for phosphotransfer.