Reciprocally Coupled Residues Crucial for Protein Kinase Pak2 Activity Calculated by Statistical Coupling Analysis

Regulation of Pak2 activity involves at least two mechanisms: (i) phosphorylation of the conserved Thr402 in the activation loop and (ii) interaction of the autoinhibitory domain (AID) with the catalytic domain. We collected 482 human protein kinase sequences from the kinome database and globally mapped the evolutionary interactions of the residues in the catalytic domain with Thr402 by sequence-based statistical coupling analysis (SCA). Perturbation of Thr402 (34.6%) suggests a communication pathway between Thr402 in the activation loop, and Phe387 (ΔΔE387F,402T = 2.80) in the magnesium positioning loop, Trp427 (ΔΔE427W,402T = 3.12) in the F-helix, and Val404 (ΔΔE404V,402T = 4.43) and Gly405 (ΔΔE405G,402T = 2.95) in the peptide positioning loop. When compared to the cAMP-dependent protein kinase (PKA) and Src, the perturbation pattern of threonine phosphorylation in the activation loop of Pak2 is similar to that of PKA, and different from the tyrosine phosphorylation pattern of Src. Reciprocal coupling analysis by SCA showed the residues perturbed by Thr402 and the reciprocal coupling pairs formed a network centered at Trp427 in the F-helix. Nine pairs of reciprocal coupling residues crucial for enzymatic activity and structural stabilization were identified. Pak2, PKA and Src share four pairs. Reciprocal coupling residues exposed to the solvent line up as an activation groove. This is the inhibitor (PKI) binding region in PKA and the activation groove for Pak2. This indicates these evolutionary conserved residues are crucial for the catalytic activity of PKA and Pak2.