Decoding Inhibitor Egression from Wild-Type and G2019S Mutant LRRK2 Kinase: Insights into Unbinding Mechanisms for Precision Drug Design in Parkinson's Disease.

Leucine-rich repeat kinase 2 (LRRK2) remains a viable target for drug development since the discovery of the association of its mutations with Parkinson's disease (PD). G2019S (in the kinase domain) is the most common mutation for LRRK2-based PD. Though various types of inhibitors have been developed for the kinase domain to reduce the effect of the mutation, understanding the working of these inhibitors at the molecular level is still ongoing. This study focused on the exploration of the dissociation mechanism (pathways) of inhibitors from (WT and G2019S) LRRK2 kinase (using homology model CHK1 kinase), which is one of the crucial aspects in drug discovery. Here, two ATP-competitive type I inhibitors, PF-06447475 and MLi-2 (Comp1 and Comp2 ), and one non-ATP-competitive type II inhibitor, rebastinib (Comp3), were considered for this investigation. To study the unbinding process, random accelerated molecular dynamics simulations were performed. The binding free energies of the three inhibitors for different egression paths were determined using umbrella sampling. This work found four major egression pathways that were adopted by the inhibitors Comp1 (path1, path2, and path3), Comp2 (path1, path2 and path3), and Comp3 (path3 and path4). Also, the mechanism of unbinding for each path and key residues involved in unbinding were explored. Mutation was not observed to impact the preference of the particular egression pathways for both LRRK2-Comp1 and -Comp2 systems. However, the findings suggested that the size of the inhibitor molecules might have an effect on the preference of the egression pathways. The binding energy and residence time of the inhibitors followed a similar trend to experimental observations. The findings of this work might provide insight into designing more potent inhibitors for the G2019S LRRK2 kinase.

Structural insight into G2019S mutated LRRK2 kinase and brain-penetrant type I inhibitor complex: a molecular dynamics approach.

More than 40 mutations in the multidomain leucine-rich repeat kinase 2 (LRRK2) are found and mutation G2019S in the kinase domain is the most concerned with Parkinson's disease (PD). The discovery of the various types of inhibitors has largely emerged recently. However, the comparative study on molecular insight in WT and G2019S LRRK2 kinase domain upon binding of the inhibitors has not yet been explored in detail. This work considered five ATP-competitive Type I inhibitors complexed with WT and mutated LRRK2 kinase. Three reported potent and brain-penetrant inhibitors, GNE-7915, PF-06447475 and MLi-2 (comp1, comp2 and comp3 respectively) and also, another two inhibitors, Pyrrolo[2,3-b] pyridine derivative (comp4) and Pyrrolo[2,3-d] pyrimidine derivative (comp5), were used. In this work, classical and accelerated molecular dynamics (cMD and aMD) simulations were performed for a total of 12 systems (apo and holo). This study found structural and thermodynamic stability for all the inhibitors. Comparatively larger molecules (size 15.3 - 15.4 Å), comp1, comp3 and comp5, showed more selectivity towards mutated LRRK2 kinase in terms of flexibility of residues, compactness and dynamics of kinase, the stability inside the binding-pocket. Also, inhibitors comp3 and comp5 showed higher binding affinity towards G2019S LRRK2 among the five. Residues, E1948 and A1950 (in hinge region) were observed mainly to form hydrogen bonds with inhibitors. Finally, MLi-2 showed a conformational rearrangement by dihedral flipping in both WT and mutated systems but got stability in G2019S LRRK2. This work could potentially help design more improved and effective Type I inhibitors for G2019S LRRK2 kinase.

Role of the Residue Q1919 in Increasing Kinase Activity of G2019S LRRK2 Kinase: A Computational Study.

Mutations in multi-domain leucine-rich repeat kinase 2 (LRRK2) have been an interest to researchers as these mutations are associated with Parkinson's disease. G2019S mutation in LRRK2 kinase domain leads to the formation of additional hydrogen bonds by S2019 which results in stabilization of the active state of the kinase, thereby increasing kinase activity. Two additional hydrogen bonds of S2019 are reported separately. Here, a mechanistic picture of the formation of additional hydrogen bonds of S2019 with Q1919 (also with E1920) is presented using 'active' Roco4 kinase as a homology model and its relationship with the stabilization of the 'active' G2019S LRRK2 kinase. A conformational flipping of residue Q1919 was found which helped to form stable hydrogen bond with S2019 and made 'active' state more stable in G2019S LRRK2. Two different states were found within the 'active' kinase with respect to the conformational change (flipping) in Q1919. Two doubly-mutated systems, G2019S/Q1919A and G2019S/E1920 K, were studied separately to check the effect of Q1919 and E1920. For both cases, the stable S2 state was not formed, leading to a decrease in kinase activity. These results indicate that both the additional hydrogen bonds of S2019 (with Q1919 and E1920) are necessary to stabilize the active G2019S LRRK2.