The Very C-Terminus of Protein Kinase Cɛ is Critical for the Full Catalytic Competence but its Hydrophobic Motif is Dispensable for the Interaction with 3-Phosphoinositide-Dependent Kinase-1

In this article, we explore the role of the C-terminus (V5 domain) of PKCɛ plays in the catalytic competence of the kinase using serial truncations followed by immune-complex kinase assays. Surprisingly, removal of the last seven amino acid residues at the C-terminus of PKCɛ resulted in a PKCɛ-Δ731 mutant with greatly reduced intrinsic catalytic activity while truncation of eight amino acid residues at the C-terminus resulted in a catalytically inactive PKCɛ mutant. Computer modeling and molecular dynamics simulations showed that the last seven and/or eight amino acid residues of PKCɛ were involved in interactions with residues in the catalytic core. Further truncation analyses revealed that the hydrophobic phosphorylation motif was dispensable for the physical interaction between PKCɛ and 3-phosphoinositide-dependent kinase-1 (PDK-1) as the PKCɛ mutant lacking both the turn and the hydrophobic motifs could still be co-immunoprecipitated with PDK-1. These results provide fresh insights into the biochemical and structural basis underlying the isozyme-specific regulation of PKC and suggest that the very C-termini of PKCs constitute a promising new target for the development of novel isozyme-specific inhibitors of PKC