The SARS-CoV-2 main protease (Mpro) is essential for replication of the virus responsible for the COVID-19 pandemic, and one of the main targets for drug design. Here, we simulate the...

The environmental problems derived from the generalized plastic consumption and disposal could find a friendly solution in enzymatic biodegradation. Recently, two hydrolases from Ideonella sakaiensis 201-F6 and the metagenome-derived leaf-branch compost cutinase (LCC), more specially the improved ICCG variant, have revealed degradation activity toward poly ethylene terephthalate (PET). In the present study, the reaction mechanism of this polymer breakage is studied at an atomic level by multiscale QM/MM molecular dynamics simulations, using semiempirical and DFT Hamiltonians to describe the QM region. The obtained free energy surfaces confirmed a characteristic four-step path for both systems, with activation energies in agreement with the experimental observations. Structural analysis of the evolution of the active site along the reaction progress and the study of electrostatic effects generated by the proteins reveal the similarity in the behavior of the active site of these two enzymes. The origin of the apparent better performance of the LCC-ICCG protein over PETase must be due to its capabilities of working at higher temperature and its intrinsic relationship with the crystallinity grade of the polymer. Our results may be useful for the development of more efficient enzymes in the biodegradation of PET.

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In this work a computational study of the mechanism of inhibition of cruzain, rhodesain, and cathepsin L cysteine proteases by the dipeptidyl nitroalkene Cbz‐Phe‐Ala‐CH=CH‐NO2 has been carried out by means of molecular dynamics simulations with hybrid QM/MM potentials. The free‐energy surfaces confirmed that the inhibition takes place by the formation of a covalent bond between the protein and the β‐carbon atom of the inhibitor. According to the results, the tested inhibitor should be a much more efficient inhibitor of cruzain than of rhodesain, and little activity would be expected against cathepsin L, in total correspondence with the available experimental data. The origin of these differences may lie in the different stabilizing electrostatic interactions established between the inhibitor and the residues of the active site and S2 pocket of these enzymes. These results may be useful for the rational design of new dipeptidyl nitroalkenes with higher and more selective inhibitory activity against cysteine proteases.

Cruzain is a primary cysteine protease expressed by the protozoan parasite Trypanosoma cruzi during Chagas disease infection, and thus, the development of inhibitors of this protein is a promising target for designing an effective therapy against the disease. In this paper, the mechanism of inhibition of cruzain by two different irreversible peptidyl halomethyl ketones (PHK) inhibitors has been studied by means of hybrid quantum mechanics/molecular mechanics−molecular dynamics (MD) simulations to obtain a complete representation of the possible free energy reaction paths. These have been traced on free energy surfaces in terms of the potential of mean force computed at AM1d/MM and DFT/MM levels of theory. An analysis of the possible reaction mechanisms of the inhibition process has been performed showing that the nucleophilic attack of an active site cysteine, Cys25, on a carbon atom of the inhibitor and the cleavage of the halogen−carbon bond take place in a single step. PClK appears to be much more favorable than PFK from a kinetic point of view. This result would be in agreement with experimental studies in other papain-like enzymes. A deeper analysis of the results suggests that the origin of the differences between PClK and PFK can be the different stabilizing interactions established between the inhibitors and the residues of the active site of the protein. Any attempt to explore the viability of the inhibition process through a stepwise mechanism involving the formation of a thiohemiketal intermediate and a three-membered sulfonium intermediate has been unsuccessful. Nevertheless, a mechanism through a protonated thiohemiketal, with participation of His159 as a proton donor, appears to be feasible despite showing higher free energy barriers. Our results suggest that PClK can be used as a starting point to develop a proper inhibitor of cruzain.