RESUMO
Trypanosoma cruzi, a flagellate protozoan parasite, is responsible for Chagas disease. The parasite major cysteine protease, cruzain (Cz), plays a vital role at every stage of its life cycle and the active-site region of the enzyme, similar to those of other members of the papain superfamily, is well characterized. Taking advantage of structural information available in public databases about Cz bound to known covalent inhibitors, along with their corresponding activity annotations, in this work, we performed a deep analysis of the molecular interactions at the Cz binding cleft, in order to investigate the enzyme inhibition mechanism. Our toolbox for performing this study consisted of the charge density topological analysis of the complexes to extract the molecular interactions and machine learning classification models to relate the interactions with biological activity. More precisely, such a combination was useful for the classification of molecular interactions as "active-like" or "inactive-like" according to whether they are prevalent in the most active or less active complexes, respectively. Further analysis of interactions with the help of unsupervised learning tools also allowed the understanding of how these interactions come into play together to trigger the enzyme into a particular conformational state. Most active inhibitors induce some conformational changes within the enzyme that lead to an overall better fit of the inhibitor into the binding cleft. Curiously, some of these conformational changes can be considered as a hallmark of the substrate recognition event, which means that most active inhibitors are likely recognized by the enzyme as if they were its own substrate so that the catalytic machinery is arranged as if it is about to break the substrate scissile bond. Overall, these results contribute to a better understanding of the enzyme inhibition mechanism. Moreover, the information about main interactions extracted through this work is already being used in our lab to guide docking solutions in ongoing prospective virtual screening campaigns to search for novel noncovalent cruzain inhibitors.
RESUMO
We report here two new small-size peptides acting as modulators of the ß-site APP cleaving enzyme 1 (BACE1) exosite. Ac-YPYFDPL-NH2 and Ac-YPYDIPL-NH2 displayed a moderate but significant inhibitory effect on BACE1. These peptides were obtained from a molecular modeling study. By combining MD simulations with ab initio and DFT calculations, a simple and generally applicable procedure to evaluate the binding energies of small-size peptides interacting with the exosite of the BACE1 is reported here. The structural aspects obtained for the different complexes were analyzed providing a clear picture about the binding interactions of these peptides. These interactions have been investigated within the framework of the density functional theory and the quantum theory of atoms in molecules using a reduced model. Although the approach used here was traditionally applied to the study of noncovalent interactions in small molecules complexes in gas phase, we show, through in this work, that this methodology is also a very powerful tool for the study of biomolecular complexes, providing a very detailed description of the binding event of peptides modulators at the exosite of BACE1.