Catalytic activity in vitro of the human protein kinase ASK1 mutants: Experimental and molecular simulation study

Kinases have become an important class of targets for drug discovery since the milestone approval of imatinib in 2001. Although a great success has been achieved for targeting kinases with over 70 inhibitors approved by the FDA, it is inevitable that drug resistance would emerge during treatment. Thus, assessment of the kinase mutations is an essential issue for the development of the next generation inhibitors. Apoptosis signal-regulating kinase 1 (ASK1) is a crucial regulator of classical mitogen-activated protein kinase cascade that is being explored under several clinical trials as a promising target. Herein, we investigate the catalytic activity in vitro of ASK1 by constructing two mutants: M754T and H729L, from gatekeeper and alpha C-helix, respectively. Compared to wild type, the mutation of M754T and H729L results in a roughly 3-fold and 2-fold decrease in binding affinity experimentally. In addition, their binding modes with substrate are theoretically predicted and compared by molecular dynamics. Trajectory analyses of simulations indicate that the decrease of binding affinity should be attributed to the loss of H-bond interaction with gatekeeper methionine. Unexpectedly, the conformation of alpha Chelix in H729L mutant did not alter significantly during the simulations, although the putatively important Hbond with H729 is lost. These simulations showed the regulatory role of H729 in alpha C-helix is maintained by leucine residue through the interaction with non-polar residues around H729 site.

Automated summary

Kinases have been successfully targeted for drug discovery, but drug resistance is a concern. Assessing kinase mutations is essential for developing next-generation inhibitors. In this study, two mutants of ASK1 were constructed and their catalytic activity was investigated. Experimental results showed decreased binding affinity for the mutants compared to the wild type, and molecular dynamics simulations revealed the loss of hydrogen bond interaction as a possible cause for the decreased affinity.