Insights into unbinding mechanisms upon two mutations investigated by molecular dynamics study of GSK3beta-axin complex: role of packing hydrophobic residues

Glycogen synthase kinase 3beta (GSK 3beta) is a key component of several cellular processes including Wnt and insulin signalling pathways. The interaction of GSK3beta with scaffolding peptide axin is thought to be responsible for the effective phosphorylation of beta-catenin, the core effector of Wnt signaling, which has been linked with the occurrence of colon cancer and melanoma. It has been demonstrated that the binding of axin to GSK3beta is abolished by the single-point mutation of Val267 to Gly (V267G) in GSK3beta or Leu392 to Pro (L392P) in axin. Molecular dynamics (MD) simulations were performed on wild type (WT), V267G mutant and L392P one to elucidate the two unbinding mechanisms that occur through different pathways. Besides, rough energy and residue-based energy decomposition were calculated by MM_GBSA (molecular mechanical Generalized_Born surface area) approach to illuminate the instability of the two mutants. The MD simulations of the two mutants and WT reveal that the structure of GSK3beta remains unchanged, while axin moves away from the interfacial hydrophobic pockets in both two mutants. Axin exhibits positional shift in V267G mutant, whereas, losing the hydrogen bonds that are indispensable for stabilizing the helix structure of wild type axin, the helix of axin is distorted in L392P mutant. To conclude, both two mutants destroy the hydrophobic interaction that is essential to the stability of GSK3beta-axin complex.