Conformational and Dynamical Effects of Tyr32 Phosphorylation in K-Ras: Molecular Dynamics Simulation and Markov State Models Analysis.

Phosphorylation of tyrosine 32 in K-Ras has been shown to influence function by disrupting the GTPase cycle. To shed light on the underlying mechanism and atomic basis of this process, we carried out a comparative investigation of the oncogenic G12D K-Ras mutant and its phosphorylated variant (pTyr32) using all-atom molecular dynamics simulations and Markov state models. We show that, despite sharing a number of common features, G12D and pTyr32-G12D K-Ras exhibit some distinct conformational states and fluctuations. In addition to notable differences in conformation and dynamics of residues surrounding the GTP binding site, nonlocal changes were observed at a number of loops. Switch I is more flexible in pTyr32-G12D K-Ras while switch II is more flexible in G12D K-Ras. We also used time-lagged independent component analysis and k-means clustering to identify five metastable states for each system. We utilized transition path theory to calculate the transition probabilities for each state to build a Markov state model for each system. These models and other close inspections suggest that the phosphorylation of Tyr32 strongly affects protein dynamics and the active site conformation, especially with regards to the canonical switch conformations and dynamics.