Study of interaction energies between residues of the active site of Hsp90 and geldanamycin analogues using quantum mechanics/molecular mechanics methods.

Background: Heat shock protein (Hsp90KDa) is a molecular chaperone involved in the process of cellular oncogenesis, hence its importance as a therapeutic target. Geldanamycin is an inhibitor of Hsp90 chaperone activity, which binds to the ATP binding site in the N-terminal domain of Hsp90. However, geldanamycin has shown hepatotoxic damage in clinical trials; for this reason, its use is not recommended. Taking advantage that geldanamycin binds successfully to Hsp90, many efforts have focused on the search for similar analogues, which have the same or better biological response and reduce the side effects of its predecessor; 17-AAG and 17-DMAG are examples of these analogues. Methods: In order to know the chemical factors influencing the growth or decay of the biological activity of geldanamycin analogues, different computational techniques such as docking, 3DQSAR and quantum similarity were used.  Moreover, the study quantified the interaction energy between amino acids residues of active side and geldanamycin analogues, through hybrid methodology (Autodock-PM6) and DFT indexes. Results: The evaluation of interaction energies showed that the interaction with Lys58 residue is essential for the union of the analogues to the active site of Hsp90, and improves its biological activity. This union is formed through a substituent on C-11 of the geldanamycin macrocycle. A small and attractor group was found as the main steric and electrostatic characteristic that substituents on C11 need in order to interact with Lys 58; behavior was observed with hydroxy and methoxy series of geldanamycin analogues, under study. Conclusion: This study contributes with new hybrid methodology (Autodock-PM6) for the generation of 3DQSAR models, which to consider the interactions between compounds and amino acids residues of Hsp90´s active site in the alignment generation. Additionally, quantum similarity and reactivity indices calculations using DFT were performed to know the non-covalent stabilization in the active site of these compounds.

Application of molecular docking and ONIOM methods for the description of interactions between anti-quorum sensing active (AHL) analogues and the Pseudomonas aeruginosa LasR binding site.

Molecular docking methods were applied to simulate the coupling of a set of nineteen acyl homoserine lactone analogs into the binding site of the transcriptional receptor LasR. The best pose of each ligand was explored and a qualitative analysis of the possible interactions present in the complex was performed. From the results of the protein-ligand complex analysis, it was found that residues Tyr-64 and Tyr-47 are involved in important interactions, which mainly determine the antagonistic activity of the AHL analogues considered for this study. The effect of different substituents on the aromatic ring, the common structure to all ligands, was also evaluated focusing on how the interaction with the two previously mentioned tyrosine residues was affected. Electrostatic potential map calculations based on the electron density and the van der Waals radii were performed on all ligands to graphically aid in the explanation of the variation of charge density on their structures when the substituent on the aromatic ring is changed through the elements of the halogen group series. A quantitative approach was also considered and for that purpose the ONIOM method was performed to estimate the energy change in the different ligand-receptor complex regions. Those energy values were tested for their relationship with the corresponding IC50 in order to establish if there is any correlation between energy changes in the selected regions and the biological activity. The results obtained using the two approaches may contribute to the field of quorum sensing active molecules; the docking analysis revealed the role of some binding site residues involved in the formation of a halogen bridge with ligands. These interactions have been demonstrated to be responsible for the interruption of the signal propagation needed for the quorum sensing circuit. Using the other approach, the structure-activity relationship (SAR) analysis, it was possible to establish which structural characteristics and chemical requirements are necessary to classify a compound as a possible agonist or antagonist against the LasR binding site.

Método acoplado Autodock-PM6 para seleccionar la mejor pose en estudios de acoplamiento molecular / Autodock-PM6 method to choose the better pose in molecular docking studies / A Autodock-PM6 metodo pra seleccionar o melhor pose en estudios de acoplamiento molecular

El acoplamiento molecular (conocido como docking) es una técnica de mecánica molecular ampliamente utilizada para predecir energías y modos de enlace entre ligandos y proteínas, información de gran utilidad en el estudio de nuevos compuestos con efectos terapéuticos. No obstante, los resultados obtenidos mediante esta técnica tienden a la subjetividad, debido a que los programas utilizados para llevarla a cabo proporcionan más de un criterio de selección de la mejor pose. En la presente investigación se aplicó el método semiempírico PM6 a los resultados del acoplamiento, obteniendo con ello mejorías en el proceso de selección de la mejor pose pues se obtuvieron poses con alta probabilidad de unión al sitio activo de su receptor y con energías de unión menores a las reportadas por los criterios de selección ofrecidos por el programa de docking.

The acoplamiento molecular (conocido como docking) es una técnica de mecánica molecular ampliamente utilizada para predecir energías y modos de enlace entre ligandos y proteínas, lo que proporciona información de gran utilidad para el estudio de nuevos compuestos con efectos terapéuticos. No obstante, los resultados obtenidos mediante esta técnica tienden a la subjetividad, debido a que los programas utilizados para llevarla a cabo proporcionan más de un criterio de selección de la mejor pose. En la presente investigación, se aplicó el método semiempírico PM6 a los resultados del acoplamiento, obteniendo con ello mejorías en el proceso de selección de la mejor pose al observarse finalmente poses con alta probabilidad de unión al sitio activo de su receptor y con energías de unión menores a las reportadas por los criterios de selección ofrecidos por el programa de docking.

El acoplamiento molecular (conocido como docking) es una técnica de mecánica molecular ampliamente utilizada para predecir energías y modos de enlace entre ligandos y proteínas, lo que proporciona información de gran utilidad para el estudio de nuevos compuestos con efectos terapéuticos. No obstante, los resultados obtenidos mediante esta técnica tienden a la subjetividad, debido a que los programas utilizados para llevarla a cabo proporcionan más de un criterio de selección de la mejor pose. En la presente investigación, se aplicó el método semiempírico PM6 a los resultados del acoplamiento, obteniendo con ello mejorías en el proceso de selección de la mejor pose al observarse finalmente poses con alta probabilidad de unión al sitio activo de su receptor y con energías de unión menores a las reportadas por los criterios de selección ofrecidos por el programa de docking.

Quantum mechanics study of the hydroxyethylamines-BACE-1 active site interaction energies.

The identification of BACE-1, a key enzyme in the production of Amyloid-ß (Aß) peptides, generated by the proteolytic processing of amyloid precursor protein, was a major advance in the field of Alzheimer's disease as this pathology is characterized by the presence of extracellular senile plaques, mainly comprised of Aß peptides. Hydroxyethylamines have demonstrated a remarkable potential, like candidate drugs, for this disease using BACE-1 as target. Density Functional Theory calculations were employed to estimate interaction energies for the complexes formed between the hydroxyethylamine derivated inhibitors and 24 residues in the BACE-1 active site. The collected data offered not only a general but a particular quantitative description that gives a deep insight of the interactions in the active site, showing at the same time how ligand structural variations affect them. Polar interactions are the major energetic contributors for complex stabilization and those ones with charged aspartate residues are highlighted, as they contribute over 90% of the total attractive interaction energy. Ligand-ARG296 residue interaction reports the most repulsive value and decreasing of the magnitude of this repulsion can be a key feature for the design of novel and more potent BACE-1 inhibitors. Also it was explained why sultam derivated BACE-1 inhibitors are better ones than lactam based. Hydrophobic interactions concentrated at S1 zone and other relevant repulsions and attractions were also evaluated. The comparison of two different theory levels (X3LYP and M062X) allowed to confirm the relevance of the detected interactions as each theory level has its own strength to depict the forces involved, as is the case of M062X which is better describing the hydrophobic interactions. Those facts were also evaluated and confirmed by comparing the quantitative trend, of selected ligand-residue interactions, with MP2 theory level as reference standard method for electrostatic plus dispersion energies.

Quantitative structure-retention relationships of polycyclic aromatic hydrocarbons gas-chromatographic retention indices.

Polycyclic aromatic compounds (PAHs) are of concern in environmental chemistry and toxicology. In the present work, a QSRR study was performed for 209 previously reported PAHs using quantum mechanics and other sources descriptors estimated by different approaches. The B3LYP/6-31G* level of theory was used for geometrical optimization and quantum mechanics related variables. A good linear relationship between gas-chromatographic retention index and electronic or topologic descriptors was found by stepwise linear regression analysis. The molecular polarizability (alpha) and the second order molecular connectivity Kier and Hall index ((2)chi) showed evidence of significant correlation with retention index by means of important squared coefficient of determination, (R(2)), values (R(2)=0.950 and 0.962, respectively). A one variable QSRR model is presented for each descriptor and both models demonstrates a significant predictive capacity established using the leave-many-out LMO (excluding 25% of rows) cross validation method's q(2) cross-validation coefficients q(2)(CV-LMO25%), (obtained q(2)(CV-LMO25%) 0.947 and 0.960, respectively). Furthermore, the physicochemical interpretation of selected descriptors allowed detailed explanation of the source of the observed statistical correlation. The model analysis suggests that only one descriptor is sufficient to establish a consistent retention index-structure relationship. Moderate or non-significant improve was observed for quantitative results or statistical validation parameters when introducing more terms in predictive equation. The one parameter QSRR proposed model offers a consistent scheme to predict chromatographic properties of PAHs compounds.