Available for structural studies of both MRCK and ROCK kinases should allow iterative drug development approaches. ATP competitive kinase inhibitors have been widely used to identify signaling pathways. In some cases, however, pharmacological observations do not support the biochemical data. One example is the acetylcholine induced suppression of the M-type potassium channel It has been known that this regulation involves protein kinase C activation. However, some PKC inhibitors do not prevent the suppression of the M-current induced by muscarinic agonists, which once led to an exclusion of PKC from the list of candidate mediators. We found that this discrepancy is due to a PKC associating protein, AKAP79/ 150, which tethers PKC in the M-channel complex. We demonstrated that AKAP79/150 bound PKC cannot interact with some PKC inhibitors, such as bisindolylmaleimide I, since the pseudosubstrate-like domain in the PKC binding domain of AKAP79/150 competes with BIS I binding. Through this study, we identified BIS I as a competitive inhibitor with respect to substrate peptides. In addition, we found that a related molecule, BIS IV, is an uncompetitive inhibitor for the substrate peptide. These results suggest that ATP competitive PKC inhibitors can modify how PKC interacts with substrate peptides. Potential 581073-80-5 interactions between substrate peptides and ATP competitors are also suggested by crystal structure studies. To date, several crystal structures of PKC-inhibitor complexes have been solved. These analyses demonstrated that such ATP competitor molecules make hydrogen bonds with residues located in the substrate recognition groove. Thus, the structural information is consistent with a hypothesis that some PKC inhibitors compete not only with ATP but also with substrate peptides or pseudosubstrates. However, how ATP competitive kinase inhibitors interact with the pseudosubstrate domain remains unknown. The pseudosubstrate domain governs the activation status of many serine/threonine kinases. PKC is a typical example of such kinases. In the quiescent state, the pseudosubstrate covers the MGCD0103 catalytic site so that no substrate proteins can be phosphorylated. Upon activation, a conformational change uncovers the catalytic site from the pseudosubstrate domain. This allows substrate proteins to enter the catalytic site for phosphorylation. In this paper, we investigate functional consequences of the interaction between the intramolecular pseudosubstrate domain of PKC and ATP competitive inhibitors. We show that the primary target for BIS I is activated PKC while BIS IV targets quiescent PKC. We demonstrate that these different state-dependent inhibitions change the activation kinetics of PKC and stabilize PKC in certain conformations within the cellular environme
