Biochemical evidence for the interaction of regulatory subunit of cAMP‐dependent protein kinase with IDA (Inter‐DFG‐APE) region of catalytic subunit

Abstract

To explore the structural basis required for the holoenzyme formation of cAMP-dependent protein kinase, we have prepared rabbit anti-peptide antibodies that can block the holoenzyme formation without affecting the catalytic activity of the enzyme. The antibodies were raised against a specific site in the catalytic (C)-subunit, termed IDA (Inter-DFG-APE) region, which lies between the kinase subdomains VII and VIII. Although the C-subunit immunoprecipitated with anti-IDA antibodies could not form a stable complex with regulatory (R)-subunit, it was still susceptible to inhibition by the R-subunit or by PKI, a specific inhibitor peptide containing a pseudosubstrate site. These results indicate that there exists an IDA region-mediated interaction between the R- and C-subunits, which is distinct from that mediated through the substrate site and substrate binding site. In accordance with this idea, association of synthetic IDA peptides with the R-subunit was directly demonstrated by resonance mirror analysis. The calculated association constants of IDA peptides were high enough to suggest a possible involvement of the IDA region in the initial step of holoenzyme formation.