A Model for the Chemical Interactions of Adenosine 3':5'-Monophosphate with the R Subunit of Protein Kinase Type I. Refinement of the Cyclic Phosphate Binding moiety of Protein Kinase Type I

Abstract

The cyclic[c]AMP receptor site in the regulatory subunit of cAMP-dependent protein kinase type I [from rabbit muscle] was mapped using analogs of cAMP in which the ribose phosphate moiety was systematically modified. Electronical alteration of the cyclophosphate ring at the 3'' and 5'' positions by S and N decreased the affinity of these analogs towards the kinase. Substituents at these positions are not tolerated. Testing the separated diastereomers of derivatives in which 1 of the exocyclic oxygens at the phosphorus was substituted by S, it was found that 1 diastereoisomer is preferentially recognized. The hydrophylic cyclic phosphate-ribose moiety of cAMP is probably bound to the kinase via its 3'' and 5''-oxygens, the 2''-hydroxy group and the negative charge in a fixed position. The adenine moiety is probably bound in a hydrophobic cleft without any H-bond interactions. The chemical interactions between cAMP and the R subunit of protein kinase type I differ from those found for the binding of cAMP to the chemoreceptor of Dictyostelium discoideum.