Hydrophobic Features Research Articles

Structure-Based Drug Designing Recommends HDAC6 Inhibitors To Attenuate Microtubule-Associated Tau-Pathogenesis.

Protein acetylation and deacetylation play vital roles in the structural and physiological behavior of target proteins. Histone deacetylase 6 (HDAC6) remains a key therapeutic target in several chronic diseases such as cancer, neurodegenerative, and hematological diseases. In tau-pathogenesis, HDAC6 tightly regulates microtubule-associated tau physiology, and its inhibition suppresses Alzheimer's phenotype. To this end, the current study has identified novel HDAC6 inhibitors by structure-based drug designing method. A pharmacophore was generated from HDAC6 in complex with trichostatin A. The selected pharmacophore had five features including two hydrogen bond donors, one hydrogen bond acceptor, and two hydrophobic features. Pharmacophore validation obtained the highest GH score of 0.80. By applying Lipinski's rule of five and ADMET Descriptors, a drug-like database of 29 183 molecules was generated from the Zinc Natural Product Database. The validated pharmacophore screened 841 drug-like molecules and was subsequently subjected to molecular docking in the active site of HDAC6. Molecular docking identified 11 hits, where they showed the highest ChemPLP score (>90.00), stable conformation, and hydrogen-bond interactions with catalytic residues of HDAC6. Finally, molecular dynamics simulation identified three molecules as potent HDAC6 inhibitors with stable root-mean-square deviation and the highest number of hydrogen bonds with the catalytic residues of HDAC6. Overall, we recommend three novel inhibitors of HDAC6, capable of suppressing the microtubule-associated tau-pathogenesis.

Pharmacophore-based virtual screening for identification of potential selective inhibitors of human histone deacetylase 6

Histone deacetylase (HDAC) 6 plays a role in oncogenic transformation and cancer metastasis via tubulin deacetylation, making it a critical target for anticancer drug design. However, lack of selectivity shown by many of the current HDAC6 inhibitors in clinical use and trials prompts the continuous search for selective inhibitors. Here, 10 pharmacophore hypotheses were developed based on the 3D common features of training set of 20 HDAC inhibitors in clinical use and trials. The hypotheses were validated using a test set of another 20 HDAC inhibitors along with 400 inactive (decoys) molecules based on Güner-Henry pharmacophore scoring method. Hypothesis 1 consisting of 1 H-bond donor, 1 H-bond acceptor and 2 hydrophobic features, was used to screen “DruglikeDiverse” database using Biovia Discovery Studio 4.5. The top 10 hit compounds were selected based on the pharmacophore fit values (>3.00). Their binding affinity against HDAC6 compared to class I HDACs (1, 2, 3 & 8) and a class IIa member (HDAC7), was calculated by molecular docking using AutoDock4. The stability of binding modes of 2 potential HDAC6-selective inhibitors (ENA501965 and IBS399024) was examined by 30 ns-molecular dynamics (MD) simulation using nanoscale MD (NAMD) software. Both ligands showed potential stability in HDAC6 active site over time. Therefore, these may provide additional scaffolds for further optimization towards the design of safe, potent and selective HDAC6 inhibitors.

Red pepper Capsicum baccatum: source of antiadhesive and antibiofilm compounds against nosocomial bacteria

Currently, there is a great interest in the search for new natural bioactive compounds against bacterial biofilms, ubiquitous in natural, clinical and industrial environments, and responsible for the high resistance of bacteria to antimicrobial agents. Several species of Capsicum red peppers are used worldwide in a number of preparations to treat a variety of illnesses, including infections. The aim of this study was to investigate the antiadhesive and antibiofilm activity of Capsicum baccatum, after sequential extraction, against important bacteria. Antimicrobial and antibiofilm activities against Staphylococcus epidermidis and Pseudomonas aeruginosa were performed by the OD600 absorbance and crystal violet method, respectively, and using scanning electron microscopy (SEM). The most active extract of C. baccatum was incorporated in Permanox™ slides by spin-coated technique in order to produce an anti-infective surface. In addition, an in vivo toxicological evaluation was performed using the alternative host model of Galleria mellonella larvae. The residual aqueous extract from C. baccatum seeds (RAqS) was the most active extract, able to inhibit up to 80% and 60% of the S. epidermidis and P. aeruginosa biofilm, respectively, without inhibiting the planktonic bacterial growth, neither promoting acute toxicity in G. mellonella. The surface coating with the RAqS modified the highly hydrophobic feature of Permanox™ slides and prevented the bacterial adhesion and biofilm development. SEM analysis showed the presence of only small clusters or individual cells without the presence of matrix on the RAqS treated samples, even when RAqS was in solution or as coating. The phytochemical evaluation of RAqS indicated the main presence of tannins and amino acids/proteins. The study presented herein demonstrated, for the first time, the ability of C. baccatum to prevent bacterial adhesion and biofilm formation of two significant pathogens. This property of C. baccatum evidences its potential as a promising source of natural compounds for the development of novel strategies, targeting anti-virulence factors, for combating antibiotic-resistant bacteria, and controlling clinical and industrial problems related to biofilms.

Estrogen receptor-based multi-residue screening of bisphenol compounds in urine.

Human exposure to bisphenol compounds (BPs) has been implicated in the development of several chronic diseases. Instead of exploiting the traditional methods for determination of BPs, this work confirms that the human estrogen receptor α ligand binding domain (hERα-LBD) is a powerful recognition element that can be used to monitor multi-residue of BPs in urine samples by fluorescence polarization (FP) assay. Test parameters were optimized for the best performance. Under the optimal conditions, the IC50 values of BPs are in the range of 0.04-1.61μgmL-1 . Recovery experiments were then performed to assess the accuracy and precision of the established method. The results detected by FP assay show good agreements with that of liquid chromatography-tandem mass spectrometry method with a fit of R2 =0.9372 and 0.9640 for BPE and BPAP, respectively. A computational methodology, ligand-based pharmacophore model, was also employed to further explore the broad-specific of tested compounds. It was found that the two hydrogen bond acceptor features and one hydrophobic aliphatic feature were essential for the corresponding cross-reactivity results from the FP assay. All these results suggest that the established method can be successfully applied to monitor the occurrence of BPs in urine.

Fabrication of low thermal conductivity yttrium silicate ceramic flat membrane for membrane distillation

This paper reports on the successful fabrication of γ-Y2Si2O7 membranes with low thermal conductivity, which is an important membrane property for achieving high performance in membrane distillation process. Single-phase γ-Y2Si2O7 powder was first synthesized by calcination of SiO2 and Y2O3 powders, with 3 wt% LiYO2 as a sintering aid. The membrane was produced by tape-casting of a suspension of this powder. After sintering at 1300 °C for 4 h, a flat membrane was obtained, which had a thickness of 0.5 mm, 49% porosity, 0.9 μm pore diameter, and low thermal conductivity of 0.497 W/m⋅K at 32 °C, and 0.528 W/m⋅K at 100 °C. The obtained membrane presented hydrophobic features (water contact angle was 132°) after surface modification, which resulted in formation of a strongly adhered robust hydrophobic SiNCO nanoparticle layer on its surface. The resultant hydrophobic membrane was tested in water desalination experiments using a sweeping gas membrane distillation (SGMD) device. High water flux of 10.07 L⋅ m−2⋅ h−1 was achieved for a 20 wt% NaCl feeding solution and a temperature at the feed of 90 °C. Stable water flux and rejection rates were recorded in long-term experiments (>400 h).

Tuning selectivity via electronic interaction: Preparation and systematic evaluation of serial polar-embedded aryl stationary phases bearing large polycyclic aromatic hydrocarbons

Aromatic stationary phases showing complementary selectivity to their alkyl counterparts are extremely useful for certain challenging separation tasks. Herein, a series of polar-embedded aryl stationary phases were synthesized from reactive derivatives of large polycyclic aromatic hydrocarbons (PAHs), including anthracene (three-ring, catacondensed), pyrene (four-ring, pericondensed) and triphenylene (four-ring, fully-benzenoid). These PAHs were functionalized with hydroxymethyl group (PAH-CH2OH), then catalytically converted to carbamates (PAH-CH2OC(=O)NH-R) using isocyanate, and finally covalently grafted onto silica to produce corresponding carbamate-embedded PAH stationary phases. To gain insight into the connection and difference among the attached species, the chromatographic behaviors of these new adsorbents were systematically evaluated in terms of surface coverage, hydrophobic and aromatic features, shape selectivity and charge-transfer property, using different classes of analytes, such as alkylbenzenes, PAH congeners and isomeric multi-substituted benzenes, and the results were further compared with conventional octadecyl ones (C18). The relationships between the shape selectivity and the surface chemistry revealed unique behavioral patterns of theses immobilized conjugated ligands, as well as marked differences amongst them, which formed sharp contrast to the case of C18. The effects of temperature and mobile phase compositions on the shape selectivity were further studied. The charge-transfer characteristics demonstrated the great potential of such polar-embedded PAH materials for highly selective separation of electron-deficient compounds through electron donor-acceptor complexation.

Synthesis of hydrophobic carbon nanotubes/reduced graphene oxide composite films by flash light irradiation

Carbon nanotubes/graphene composites have superior mechanical, electrical and electrochemistry properties with carbon nanotubes as a hydrophobicity boosting agent. Their extraordinary hydrophobic performance is highly suitable for electrode applications in lithium ion batteries and supercapacitors which often employ organic electrolytes. Also the hydrophobic features enable the oil enrichment for the crude oil separation from seawater. The ever reported synthesis routes towards such a composite either involve complicated multi-step reactions, e.g., chemical vapor depositions, or lead to insufficient extrusion of carbon nanotubes in the chemical reductions of graphene oxide, e.g., fully embedding between the compact graphene oxide sheets. As a consequence, the formation of standalone carbon nanotubes over graphene sheets remains of high interests. Herein we use the facile flash light irradiation method to induce the reduction of graphene oxides in the presence of carbon nanotubes. Photographs, micrographs, X-ray diffraction, infrared spectroscopy and thermogravimetric analysis all indicate that graphene oxides has been reduced. And the contact angle tests confirm the excellent hydrophobic performances of the synthesized carbon nanotube/reduced graphene oxide composite films. This one-step treatment represents a straightforward and high efficiency way for the reduction of carbon nanotubes/graphene oxides composites.

Discovery of High-Affinity Cannabinoid Receptors Ligands through a 3D-QSAR Ushered by Scaffold-Hopping Analysis.

Two 3D quantitative structure–activity relationships (3D-QSAR) models for predicting Cannabinoid receptor 1 and 2 (CB1 and CB2) ligands have been produced by way of creating a practical tool for the drug-design and optimization of CB1 and CB2 ligands. A set of 312 molecules have been used to build the model for the CB1 receptor, and a set of 187 molecules for the CB2 receptor. All of the molecules were recovered from the literature among those possessing measured Ki values, and Forge was used as software. The present model shows high and robust predictive potential, confirmed by the quality of the statistical analysis, and an adequate descriptive capability. A visual understanding of the hydrophobic, electrostatic, and shaping features highlighting the principal interactions for the CB1 and CB2 ligands was achieved with the construction of 3D maps. The predictive capabilities of the model were then used for a scaffold-hopping study of two selected compounds, with the generation of a library of new compounds with high affinity for the two receptors. Herein, we report two new 3D-QSAR models that comprehend a large number of chemically different CB1 and CB2 ligands and well account for the individual ligand affinities. These features will facilitate the recognition of new potent and selective molecules for CB1 and CB2 receptors.

Pharmacophore-based virtual screening for identifying β5 subunit inhibitor of 20S proteasome

Proteasomal system plays an important role in maintaining cell homeostatis. Overexpression of proteasomes leads to several major diseases, such as cancer and autoimmune disorder. The β5 subunit of proteasome is a crucial active site in proteolysis, and targeting proteasome β5 subunit is essential for proteasome inhibition. In the present study, a pharmacophore-based virtual screening and molecular docking were employed to identify ligands as inhibitors of β5 subunit of proteasome. The pharmacophore features were built with one hydrogen bond donor, two hydrogen bond acceptors, and one hydrophobic feature using native ligand of proteasome (HU10), which was then used to screen ZINC database using ZINCPharmer. The retrieved virtual hits were subjected to molecular docking analysis using iDock. The best six hits were subjected to molecular dynamics (MD) simulation and each complex was stable during 40 ns MD simulation as indicated by root-mean-square-deviation (RMSD) and root-mean-square-fluctuation (RMSF) values. The current study identifies 5 best hits having better binding potentials than HU10 as predicted by molecular mechanics Poisson-Boltzmann Surface Area (MM-PBSA) method, i.e. Lig1540/ZINC33356240, Lig1546/ZINC33356235, Lig1522/ZINC20854878, Lig980/ZINC12391945, and Lig1119/ZINC19865241, which can be used in the development of new proteasome inhibitors.

Identification of small molecule activators for ErbB 4 receptor to enhance oligodendrocyte regeneration by in silico approach

ErbB receptors are involved in regulation of proliferation, differentiation and migration of oligodendrocytes. Oligodendrocytes are myelin producing cells of CNS which ensheaths multiple axons. Regeneration of oligodendrocytes in CNS fails due to its poor regenerative potential. ErbB 4 is involved in regeneration both during adult and developmental stage via NRG 1 mediated regenerative signaling. Hence, we attempted to identify activator molecules of ErbB 4 receptor to improve this regenerative process in CNS. In current investigation, pharmacophore modeling via molecular docking and pharmacokinetics study were used to identify lead compounds for ErbB 4 activators. Selected phytochemicals were docked on tyrosine kinase domain and extracellular domain of ErbB 4 by using Autodock vina and their binding energies were analyzed. Those phytochemicals which were successfully docked on tyrosine kinase domain were subjected to in silico pharmacokinetics study by using molinspiration and swissADME. Lead compounds were identified for pharmacophore generation using ‘pharmagist’. Pharmacophore models were composed of two hydrogen bond donor, one hydrogen bond acceptor and one hydrophobic feature. Here, we report that pharmacophore generated by using Ginkgolide A, Hesperetin, Naringenin, Pelargonidin and Melatonin may serve as a good compound to develop activator of ErbB 4 receptor.

Discovery of Novel Glucagon Receptor Antagonists UsingCombined Pharmacophore Modeling and Docking.

Glucagon and the glucagon receptor are most important molecules control over blood glucose concentrations. These two molecules are very important to studies of type 2 diabetic patients. In literature, several classes of small molecule antagonists of the human glucagon receptor have been reported. Glucagon receptor antagonist could decrease hepatic glucose output and improve glucose control in diabetic patients. In this research, to identify novel and diverse leads for use in potent glucagon receptor antagonist design, a ligand-based pharmacophore modeling, was developed using the best conformations of training set compounds. The best five features pharmacophore model, called Hypo1, includes, hydrogen bond acceptors, two hydrophobic, and positive ionizable features, which has the highest correlation coefficient (0.805), cost difference (64.38), low RMS (2.148), as well as it shows a high goodness of fit and enrichment factor. The generated pharmacophore model has been validated by using a series of similar structures with varying affinities for the glucagon receptor. Then, the developed model has been applied as a search query in different database searching with the main objective of finding novel molecules which have the potential to be be modified into novel lead compounds. As a result, some hit molecules were introduced as final candidates by employing virtual screening and molecular docking procedure simultaneously. The results from pharmacophore modeling and molecular docking are complementary to each other and could serve as a useful way for the discovery of potent small molecules as glucagon receptor antagonist.

Sonication Exfoliation of Defect-Free Graphene in Aqueous Silk Nanofiber Solutions

Green processes to exfoliate graphene would be advantageous but is challenged by issues such as stability and dispersibility. Here, stable silk fibroin nanofibers (SFNs) with high crystallinity (β-sheet content) and high net negative charge were endowed with hydrophobic features yet excellent water dispersibility. These nanofibers were used to exfoliate graphite into graphene in aqueous solutions. A high concentration (1.92 mg mL–1) and yield (approaching 20%) were achieved for the exfoliated graphene dispersions using low initial graphite concentrations via sonication treatment. This approach was superior to most protein-assisted exfoliation processes reported to date, and the graphene obtained in the process exhibited fewer defects, good conductivity, and cell compatibility. The graphene prepared by this new process provided an option for SF-graphene composite materials and devices where defect-free graphene with improved performance through the introduction of SFNs into the preparation strategies will ...

Preparation of novel tissue acidosis-responsive chitosan drug nanoparticles: Characterization and in vitro release properties of Ca2+ channel blocker nimodipine drug molecules

The pH-responsive intelligent drug release facility of hydrophobically modified chitosan nanoparticles (Chit NPs) (d = 5.2 ± 1.1 nm) was presented in the case of poorly water soluble Ca2+ channel blocker nimodipine (NIMO) drug molecules. The adequate pH-sensitivity, i.e. the suitable drug carrier properties of the initial hydrophilic Chit were achieved by reductive amination of Chit with hexanal (C6-) and dodecanal (C12-) aldehydes. The successful modifications of the macromolecule were evidenced via FTIR measurements: the band appearing at 1412 cm−1 (CN stretching in aliphatic amines) in the cases of the hydrophobically modified Chit samples shows that the CN bond successfully formed between the Chit and the aldehydes. Hydrophobization of the polymer unambiguously led to lower water contents with lower intermolecular interactions in the prepared hydrogel matrix: the initial hydrophilic Chit has the highest water content (78.6 wt%) and the increasing hydrophobicity of the polymer resulted in decreasing water content (C6-chit.: 74.2 wt% and C12-chit.: 47.1 wt%). Furthermore, it was established that the length of the side chain of the aldehyde influences the pH-dependent solubility properties of the Chit. Transparent homogenous polymer solution was obtained at lower pH, while at higher pH the formation of polymer (nano)particles was determined and the corresponding cut-off pH values showed decreasing tendency with increasing hydrophobic feature (pH = 7.47, 6.73 and 2.49 for initial Chit, C6-chit and C12-chit, respectively).Next the poorly water soluble NIMO drug was encapsulated with the C6-chit with adequate pH-sensitive properties. The polymer-stabilized NIMO particles with 10 wt% NIMO content resulted in stable dispersion in aqueous phase, the formation of polymer shell increased in the water solubility/dispersibility of the initial hydrophobic drug. According to the drug release experiments, we clearly confirmed that the encapsulated low crystallinity NIMO drug remained closed in the polymer NPs at normal tissue pH (pH = 7.4, PBS buffer, physiological condition) but at pH < 6.5 which is typical for seriously ischemic brain tissue, 93.6% of the available 0.14 mg/ml NIMO was released into the buffer solution under 8 h release time. According to this in vitro study, the presented pH-sensitive drug carrier system could be useful to selectively target ischemic brain regions characterized by acidosis, to achieve neuroprotection at tissue zones at risk of injury, without any undesirable side effects caused by systemic drug administration.

Membrane Distillation Trial on Textile Wastewater Containing Surfactants Using Hydrophobic and Hydrophilic-Coated Polytetrafluoroethylene (PTFE) Membranes.

Treating wastewater from textile plants using membrane distillation (MD) has great potential due to the high-salinity wastes and availability of waste heat. However, textile wastewaters also contain surfactants, which compromise the essential hydrophobic feature of the membrane, causing membrane wetting. To address this wetting issue, a custom-made membrane consisting of a hydrophilic layer coated on hydrophobic polytetrafluoroethylene (PTFE) was tested on textile wastewater in a pilot MD setup, and compared with a conventional hydrophobic PTFE membrane. The test was carried out with a feed temperature of 60 °C, and a permeate temperature of 45 °C. The overall salt rejection of both membranes was very high, at 99%. However, the hydrophobic membrane showed rising permeate electrical conductivity, which was attributed to wetting of the membrane. Meanwhile, the hydrophilic-coated membrane showed continually declining electrical conductivity demonstrating an intact membrane that resisted wetting from the surfactants. Despite this positive result, the coated membrane did not survive a simple sodium hydroxide clean, which would be typically applied to a membrane process. This brief study showed the viability of membrane distillation membranes on real textile wastewaters containing surfactants using hydrophilic-coated hydrophobic PTFE, but the cleaning process required for membranes needs optimization.

Identification of Potentially Potent Heme Oxygenase 1 Inhibitors through 3D-QSAR Coupled to Scaffold-Hopping Analysis.

A 3D quantitative structure-activity relationship (3D-QSAR) model for predicting the activity of heme oxygenase 1 (HO-1) inhibitors was constructed with the aim of providing a useful tool for the identification, design, and optimization of novel HO-1 inhibitors. The model was built using a set of 222 HO-1 inhibitors recovered from the Heme Oxygenase Database (HemeOxDB) and developed with the software Forge. The present model showed high statistical quality, as confirmed by its robust predictive potential and satisfactory descriptive capability. The drawn-up 3D map enables prompt visual comprehension of the electrostatic, hydrophobic, and shaping features underlying the interactions with HO-1 inhibitors. A theoretical approach for the generation of new lead compounds was performed by means of scaffold-hopping analysis. For the first time, a 3D-QSAR model is reported for this target, and was built with a number of chemically diverse HO-1 inhibitors; the model also accounts well for individual ligand affinities. The new model contains all of the inhibitors published to date with high potency toward the selected target and contains a complete pharmacophore description of the binding cavity of HO-1. These features will ensure application in accelerating the identification of new potent and selective HO-1 inhibitors.

Doping Cu Atoms Excel as the Functional Material to Tune the Wettability for TMeNs Hard Coating

AbstractThe hard yet hydrophobic surface capable of withstanding harsh conditions is needed in a broad range of applications. This combined computational‐experimental study exhibits an effective modification method for transition metal nitrides protective coatings toward both excellent mechanical and robust hydrophobic properties. It indicates that the introduction of low concentrations of Cu as the solute atoms substitute for the Ta atoms in TaN lattice can form the TaCuN solid solution structure. Meanwhile, the evolution of microstructure induces the refined grains and higher H/E*, which results in a combination of improved hardness and enhanced toughness. Better yet, a moderate incorporation of solute Cu atoms into TaN structure can induce a charge depletion state and form a Cu2O surface on TaN, as demonstrated by X‐ray photoelectron spectroscopy and electron density difference pattern. The Cu2O phase has an essentially full Cu 3d shell achieving the coordinative saturation, which can inhibit hydrogen bonding with interfacial water molecules, succeeded in enhancing the hydrophobicity of TaN. Density functional theory calculations are further employed to clarify that hydrophobic feature of Cu2O groups should be responsible for the tuning of wettability via destroying hydrogen‐bonding network of water molecules next to the surface.

Effect of phase transition induced by annealing temperature on wettability, optical and photocatalytic properties of nanostructured iron oxide thin film

Nanostructured iron oxide thin films were prepared by sol–gel method and spin coating technique. The structural properties of samples were extracted from X-ray diffraction. The results indicated that the sample contained both maghemite (γ-Fe2O3) and hematite (α-Fe2O3) phases at 300 °C annealing temperature. The remainder of the maghemite phase transformed entirely to hematite by increasing annealing temperature from 300 to 500 °C. Morphological analysis showed that roughness of surface increased by annealing temperature. Fractal dimension were calculated by two methods which for both of them, it increased by annealing temperature. According to the contact angle measurement, the hydrophilic behavior converts to hydrophobic feature by changing the maghemite phase to hematite. The transparency and band gap of films decreased by phase transition from γ to α. Degradation of Rhodamine B and Methylene blue dyes with iron oxide were investigated. Increasing the annealing temperature enhanced the photocatalytic behavior due to the band gap narrowing induced by phase transition and α-Fe2O3 had the best photocatalytic degradation of MB which was reached to 95.4% in 120 min. under visible light irradiation. Whereas it exceeded than 98.6% for RhB in 135 min.

Natural rubber particle modified fabrics with catalytic activity and hydrophobicity

We report a novel and facile approach to fabricate functional fabrics using environment-friendly waterborne natural rubber latex (NRL) containing in-situ synthesized gold nanoparticles (AuNPs). AuNPs were prepared and decorated on the surface of the natural rubber particles (NRPs) by heating, forming a dual-scale hierarchical architecture. The hybrid particles of NRPs and AuNPs (AuNP@NRP) were coated on cotton and hydrophilic polyester fabric surfaces, endowing the fabrics with catalytic and hydrophobic features. The treated fabrics with low loadings of AuNP@NRP exhibited high catalytic activity for the reduction of 4-nitrophenol (4-NP) by NaBH4 and could be reused, after easy separation from the catalytic reaction system, with excellent durability. In addition, the hydrophobicity of fabrics increased as coating cycles increased. The obtained hydrophobic fabrics were used for oil/water separation, showing high separation efficiency (>96%).

Structural and biochemical characterization of the protease domain of the mosaic botulinum neurotoxin type HA.

The extreme toxicity of botulinum neurotoxins (BoNTs) relies on their specific cleavage of SNARE proteins, which eventually leads to muscle paralysis. One newly identified mosaic toxin, BoNT/HA (aka H or FA), cleaves VAMP-2 at a unique position between residues L54 and E55, but the molecular basis underlying VAMP-2 recognition of BoNT/HA remains poorly characterized. Here, we report a ∼2.09 Å resolution crystal structure of the light chain protease domain of BoNT/HA (LC/HA). Structural comparison between LC/HA and LC of BoNT/F1 (LC/F1) reveals distinctive hydrophobic and electrostatic features near the active sites, which may explain their different VAMP-2 cleavage sites. When compared to BoNT/F5 that cleaves VAMP-2 at the same site as BoNT/HA, LC/HA displays higher affinity for VAMP-2, which could be caused by their different surface charge properties surrounding a VAMP-2 exosite-binding cleft. Furthermore, systematic mutagenesis studies on VAMP-2 and structural modeling demonstrate that residues R47 to K59 spanning the cleavage site in VAMP-2 may adopt a novel extended conformation when interacting with LC/HA and LC/F5. Taken together, our structure provides new insights into substrate recognition of BoNT/HA and paves the way for rational design of small molecule or peptide inhibitors against LC/HA.

Pharmacophore and 3D-QSAR Characterization of Thieno[3,2-d] pyrimidine-6-carboxamides as SIRT-2 Inhibitors

Background: Sirtuin 2 is a deacylase enzyme which has a significant role in the treatment of neurodegenerative diseases. A reported series of novel thieno[3,2-d]pyrimidine-6- carboxamide derivatives has been chosen as sirtuin inhibitors. Methods: A pharmacophore and atom-based 3D-QSAR studies were carried out in order to understand the molecular features and structural requirement of these molecules to selectively inhibit the SIRT-2. Results: The analysis of pharmacophore model revealed two hydrogen bond acceptors, two hydrogen bond donors and one hydrophobic feature as crucial molecular features that predict binding affinity to the SIRT-2 enzyme. The pharmacophore hypothesis (AADDH.7073) derived a 3D-QSAR model with significant Partial Least Square (PLS) statistics values as r2= 0.9604, SD= 0.2568, F= 137.5, for training set and Q2= 0.9515, RMSE= 0.2045, Pearson-R= 0.9758, for the test set. Conclusion: The results provide a detailed structural insights of thieno[3,2-d]pyrimidine-6- carboxamide derivatives which can provide guidance to develop novel potent and selective SIRT-2 inhibitors. Keywords: SIRT2 inhibitor, pharmcophore, 3D-QSAR, molecular modeling, PLS, deacylase enzyme.