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

. A mutant (Serl39Ala) of the mouse recombinant catalytic (C) subunit of cAMP-dependent protein kinase was co-crystallized with a peptide inhibitor, PKI(5-24), and MEGA-8 (octanoyl-N-methylglucamide) detergent. This structure was refined using all observed data (30 248 reflections) between 30 and 1.95 Å resolution to an R factor of 0.186. R.m.s. deviations of bond lengths and bond angles are 0.013 Å and 2.3°, respectively. The final model has 3075 atoms (207 solvent) with a mean B factor of 31.9 Å². The placement of invariant protein-kinase residues and most C:PKI(5-24) interactions were confirmed, but register errors affecting residues 55-64 and 309-339 were corrected during refinement by shifting the affected sequences toward the C terminus along the previously determined backbone path. New details of C:PKI(5-24) interactions and the Ser338 autophosphorylation site are described, and the acyl group binding site near the catalytic subunit NH₂ terminus is identified.