A cell-based reporter assay for screening for EcR agonist/antagonist activity of natural ecdysteroids in Lepidoptera (Bm5) and Diptera (S2) cell cultures, followed by modeling of ecdysteroid-EcR interactions and normal mode analysis.

Ecdysteroid signal transduction is a key process in insect development and therefore an important target for insecticide development. We employed an in vitro cell-based reporter bioassay for the screening of potential ecdysone receptor (EcR) agonistic and antagonistic compounds. Natural ecdysteroids were assayed with ecdysteroid-responsive cell line cultures that were transiently transfected with the reporter plasmid ERE-b.act.luc. We used the dipteran Schneider S2 cells of Drosophila melanogaster and the lepidopteran Bm5 cells of Bombyx mori, representing important pest insects in medicine and agriculture. Measurements showed an EcR agonistic activity only for cyasterone both in S2 (EC50=3.3µM) and Bm5 cells (EC50=5.3µM), which was low compared to that of the commercial dibenzoylhydrazine-based insecticide tebufenozide (EC50=0.71µM and 0.00089µM, respectively). Interestingly, a strong antagonistic activity was found for castasterone in S2 cells with an IC50 of 0.039µM; in Bm5 cells this effect only became visible at much higher concentrations (IC50=18µM). To gain more insight in the EcR interaction, three-dimensional modeling of dipteran and lepidopteran EcR-LBD was performed. In conclusion, we showed that the EcR cell-based reporter bioassay tested here is a useful and practical tool for the screening of candidate EcR agonists and antagonists. The docking experiments as well as the normal mode analysis provided evidence that the antagonist activity of castasterone may be through direct binding with the receptor with specific changes in protein flexibility. The search for new ecdysteroid-like compounds may be particularly relevant for dipterans because the activity of dibenzoylhydrazines appears to be correlated with an extension of the EcR-LBD binding pocket that is prominent in lepidopteran receptors but less so in the modeled dipteran structure.

Relation between flexibility and positively selected HIV-1 protease mutants against inhibitors.

The antiretroviral chemotherapy helps to reduce the mortality of HIVs infected patients. However, RNA dependant virus replication has a high mutation rate. Human immunodeficiency virus Type 1 protease plays an essential role in viral replication cycle. This protein is an important target for therapy with viral protein inhibitors. There are few works using normal mode analysis to investigate this problem from the structural changes viewpoint. The investigation of protein flexibility may be important for the study of processes associated with conformational changes and state transitions. The normal mode analysis allowed us to investigate structural changes in the protease (such as flexibility) in a straightforward way and try to associate these changes with the increase of fitness for each positively selected HIV-1 mutant protease of patients treated with several protease inhibitors (saquinavir, indinavir, ritonavir, nelfinavir, lopinavir, fosamprenavir, atazanavir, darunavir, and tripanavir) in combination or separately. These positively selected mutations introduce significant flexibility in important regions such as the active site cavity and flaps. These mutations were also able to cause changes in accessible solvent area. This study showed that the majority of HIV-1 protease mutants can be grouped into two main classes of protein flexibility behavior. We presented a new approach to study structural changes caused by positively selected mutations in a pathogen protein, for instance the HIV-1 protease and their relationship with their resistance mechanism against known inhibitors. The method can be applied to any pharmaceutically relevant pathogen proteins and could be very useful to understand the effects of positively selected mutations in the context of structural changes.

The Role of QSAR and Virtual Screening Studies in Type 2 Diabetes Drug Discovery.

BACKGROUND: Due to the increasing number of diabetes cases worldwide, there is an international concern to provide even more effective treatments to control this condition. METHODS: This review brings together a selection of studies that helped to broaden the comprehension of various biological targets and associated mechanisms involved in type 2 diabetes mellitus. RESULTS: Such studies demonstrated that QSAR techniques and virtual screenings have been successfully employed in drug design projects. CONCLUSIONS: Therefore, the main goal of this review is to give the state-of-art for the development of new drugs for the treatment of type 2 diabetes mellitus and to evaluate how computational tools, such as virtual screening and 3D-QSAR, can aid the development of new drugs with reduced adverse side effects.

Structure and functional dynamics characterization of the ion channel of the human respiratory syncytial virus (hRSV) small hydrophobic protein (SH) transmembrane domain by combining molecular dynamics with excited normal modes.

The human respiratory syncytial virus (hRSV) is the major cause of lower respiratory tract infection in children and elderly people worldwide. Its genome encodes 11 proteins including SH protein, whose functions are not well known. Studies show that SH protein increases RSV virulence degree and permeability to small compounds, suggesting it is involved in the formation of ion channels. The knowledge of SH structure and function is fundamental for a better understanding of its infection mechanism. The aim of this study was to model, characterize, and analyze the structural behavior of SH protein in the phospholipids bilayer environment. Molecular modeling of SH pentameric structure was performed, followed by traditional molecular dynamics (MD) simulations of the protein immersed in the lipid bilayer. Molecular dynamics with excited normal modes (MDeNM) was applied in the resulting system in order to investigate long time scale pore dynamics. MD simulations support that SH protein is stable in its pentameric form. Simulations also showed the presence of water molecules within the bilayer by density distribution, thus confirming that SH protein is a viroporin. This water transport was also observed in MDeNM studies with histidine residues of five chains (His22 and His51), playing a key role in pore permeability. The combination of traditional MD and MDeNM was a very efficient protocol to investigate functional conformational changes of transmembrane proteins that act as molecular channels. This protocol can support future investigations of drug candidates by acting on SH protein to inhibit viral infection. Graphical Abstract The ion channel of the human respiratory syncytial virus (hRSV) small hydrophobic protein (SH) transmembrane domainᅟ.

Recovery of the wild type atomic flexibility in the HIV-1 protease double mutants.

The emergence of drug resistant mutations due to the selective pressure exerted by antiretrovirals, including protease inhibitors (PIs), remains a major problem in the treatment of AIDS. During PIs therapy, the occurrence of primary mutations in the wild type HIV-1 protease reduces both the affinity for the inhibitors and the viral replicative capacity compared to the wild type (WT) protein, but additional mutations compensate for this reduced viral fitness. To investigate this phenomenon from the structural point of view, we combined Molecular Dynamics and Normal Mode Analysis to analyze and compare the variations of the flexibility of C-alpha atoms and the differences in hydrogen bond (h-bond) network between the WT and double mutants. In most cases, the flexibility profile of the double mutants was more often similar to that of the WT than to that of the related single base mutants. All single mutants showed a significant alteration in h-bond formation compared to WT. Most of the significant changes occur in the border between the flap and cantilever regions. We found that all the considered double mutants have their h-bond pattern significantly altered in comparison to the respective single base mutants affecting their flexibility profile that becomes more similar to that of WT. This WT flexibility restoration in the double mutants appears as an important factor for the HIV-1 fitness recovery observed in patients.

Self-assembly of Arg-Phe nanostructures via the solid-vapor phase method.

We report for the first time on the self-assembly of nanostructures composed exclusively of alternating positively charged and hydrophobic amino acids. A novel arginine/phenylalanine octapeptide, RF8, was synthesized. Because the low hydrophobicity of this sequence makes its spontaneous ordering through solution-based methods difficult, a recently proposed solid-vapor approach was used to obtain nanometric architectures on ITO/PET substrates. The formation of the nanostructures was investigated under different preparation conditions, specifically, under different gas-phase solvents (aniline, water, and dichloromethane), different peptide concentrations in the precursor solution, and different incubation times. The stability of the assemblies was experimentally studied by electron microscopy and thermogravimetric analysis coupled with mass spectrometry. The secondary structure was assessed by infrared and Raman spectroscopy, and the arrays were found to assume an antiparallel ß-sheet conformation. FEG-SEM images clearly reveal the appearance of fibrillar structures that form extensive homogeneously distributed networks. A close relationship between the morphology and preparation parameters was found, and a concentration-triggered mechanism was suggested. Molecular dynamics simulations were performed to address the thermal stability and nature of intermolecular interactions of the putative assembly structure. Results obtained when water is considered as solvent shows that a stable lamellar structure is formed containing a thin layer of water in between the RF8 peptides that is stabilized by H-bonding.