Herein, for the first time, we report the flap opening and closing in Plasmepsin proteases - plasmepsin II (PlmII) was used as a prototype model. We proposed different combined parameters to define the asymmetric flap motion; the distance, d1, between the flap tip residues (Val78 and Leu292); the dihedral angle, ϕ; in addition to TriCα angles Val78-Asp34-Leu292, θ1, and Val78-Asp214-Leu292, θ2. Only three combined parameters, the distance, d1, the dihedral angle, ϕ, and the TriCα angle, θ1, were found to appropriately define the observed "twisting' motion during the flap opening and closing. The coordinated motions of the proline-rich loop adjacent to the binding cavity rim appeared to exert steric hindrance on the flap residues, driving the flap away from the active site cavity. This loop may also have increased movements around the catalytic dyad residue, Asp214, making TriCα, θ2, unreliable in describing the flap motion. The full flap opening at d1, 23.6 Å, corresponded to the largest TriCα angle, θ1, at 78.6° on a ∼46 ns time scale. Overall the average θ1 and θ2 for the bound was ∼46° and ∼53°, respectively, compared to ∼50° and ∼59° for the Apo PlmII, indicating a drastic increase in TriCα as the active site cavity opens. Similar trends in the distance, d1, and the dihedral angle, ϕ, were observed during the simulation. The asymmetrical opening of the binding cavity was best described by the large shift in ϕ from -33.91° to +21.00° corresponding to the partial opening of the flap in the range of 22-31 ns. Though, the dihedral angle described the twisting of the flap, the extent of flap opening can appropriately be defined by combining d1 and θ1. The results presented here, on the combined parameters, will certainly augment current efforts in designing potent structure-based inhibitors against plasmepsins.

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Non-nucleoside reverse transcriptase inhibitors (NNRTI) have emerged as gold standards in current anti-AIDS drug discovery and development by allosterically inhibiting HIV reverse transcriptase (HIV-RT). Connection sub-domain mutation, N348I and the M184V active site mutation decreases HIV-1 RT susceptibility to NNRTI, nevirapine (NVP), whereas concurrence of both mutations improves enzyme susceptibility to NVP. Molecular dynamics simulation and enhanced post-dynamics analyses were applied to gain molecular insight into occurrence of N348I, M184V and N348I/M184V double mutations and their effect on NVP binding landscape. Results showed that the presence of the double mutation (N348I/M184V) ameliorates the drastic effects of connection sub-domain mutation, N348I alone on NVP binding, which correlates with experimental findings. We showed that the binding of NVP to the NNRTI binding pocket (NNIBP) is drastically distorted in the presence of connection sub-domain mutation, N348I and may further explain the impaired motions of mutant RTs compared to the wild type. The residue based fluctuation further suggested that the occurrence of N348I decreased the overall flexibility of NVP-HIV-RT complex whereas concurrence of N348I/M184V double mutation restored the conformational flexibility as compared to single mutant. This phenomenon was further validated by the trends of binding free energy as well as the per-residue footprints which showed an increased ∆Gbind in case of N348I/M184V double mutant as compared to N348I variant. Further, for the first time residue interaction network highlighted the structural changes due to occurrence of M184V and N348I mutations which gives a conclusive evidence of these mutations. This work provides the most comprehensive analysis of NVP resistance and the impact of double (N348I/M184V) mutation to date from a dynamics perspective and provides information that should prove useful for understanding the drug resistance mechanism against NVP. The results also provide preliminary data which might prove useful for the design of novel inhibitors that are less susceptible to drug resistance.