No abstract

The influence of membrane environment on human cannabinoid 1 (hCB 1 ) receptor transmembrane helix (TMH) conformational dynamics was investigated by solid-state NMR and site-directed spin labeling/EPR with a synthetic peptide, hCB 1 (T377-E416), corresponding to the receptor's Cterminal component, i.e., TMH7 and its intracellular α-helical extension (H8) (TMH7/H8). Solidstate NMR experiments with mechanically aligned hCB 1 (T377-E416) specifically 2 H-or 15 Nlabeled at Ala380 and reconstituted in membrane-mimetic dimyristoylphosphocholine (DMPC) or 1-palmitoyl-2-oleoyl-sn-glycerophosphocholine (POPC) bilayers demonstrate that the conformation of the TMH7/H8 peptide is more heterogeneous in the thinner DMPC bilayer than in the thicker POPC bilayer. As revealed by EPR studies on hCB 1 (T377-E416) spin-labeled at Cys382 and reconstituted into the phospholipid bilayers, the spin label partitions actively between hydrophobic and hydrophilic environments. In the DMPC bilayer, the hydrophobic component dominates, regardless of temperature. Mobility parameters (ΔH 0 -1 ) are 0.3 and 0.73 gauss for the peptide in the DMPC or POPC bilayer environment, respectively. Interspin distances of doubly-labeled hCB 1 (T377-E416) peptide reconstituted into a TFE/H 2 0 mixture or a POPC or DMPC bilayer were estimated to be 10.6 ± 0.5, 16.8 ± 1, and 11.6 ± 0.8 Å, respectively. The extent of coupling (≥ 50%) between spin labels located at i and i+4 in a TFE/H 2 0 mixture or a POPC bilayer is indicative of an α-helical TMH conformation, whereas the much lower coupling (14%) when the peptide is in a DMPC bilayer suggests a high degree of peptide conformational heterogeneity. These data demonstrate that hCB 1 (T377-E416) backbone dynamics as well as spin-label rotameric freedom are sensitive to and altered by the peptide's phospholipid bilayer environment, which exerts a dynamic influence on the conformation of a TMH critical to signal transmission by the hCB 1 receptor.Signal-transducing G protein-coupled receptors (GPCRs) 1 are proteins that share as a common defining structural signature an intracellular carboxyl terminus, seven hydrophobic transmembrane helices (TMHs) connected by intra-and extracellular loops, and an extracellular amino terminus (1). Agonist binding is believed to induce ligand-specific GPCR structural changes that allow the receptor to assume, likely through a continuum of intermediate conformations, a functionally active state (2-4). GPCR conformation, activity, and intracellular trafficking may also be modulated by local membrane properties (e.g., tension, fluidity, lateral † This study was supported by National Institutes of Health/National Institute on Drug Abuse grants DA009158-10S2 (EKT) and DA3801(AM) and a National Science Foundation instrumentation grant CHE-0466616 (DEB). NIH Public Access Author ManuscriptBiochemistry. Author manuscript; available in PMC 2010 June 9. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript pressure) in the absence of agonist binding (5,6). Such...

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome virus 2 (SARS-CoV-2) has impacted negatively on public health and socioeconomic status, globally. Although, there are currently no specific drugs approved, several existing drugs are being repurposed, but their successful outcomes are not guaranteed. Therefore, the search for novel therapeutics remains a priority. We screened for inhibitors of the SARS-CoV-2 main protease and the receptor-binding domain of the spike protein from an integrated library of African natural products, compounds generated from machine learning studies and antiviral drugs using AutoDock Vina. The binding mechanisms between the compounds and the proteins were characterized using LigPlot+ and molecular dynamics simulations techniques. The biological activities of the hit compounds were also predicted using a Bayesian-based approach. Six potential bioactive molecules NANPDB2245, NANPDB2403, fusidic acid, ZINC000095486008, ZINC0000556656943 and ZINC001645993538 were identified, all of which had plausible binding mechanisms with both viral receptors. Molecular dynamics simulations, including molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) computations revealed stable protein-ligand complexes with all the compounds having acceptable free binding energies <−15 kJ/mol with each receptor. NANPDB2245, NANPDB2403 and ZINC000095486008 were predicted as antivirals; ZINC000095486008 as a membrane permeability inhibitor; NANPDB2403 as a cell adhesion inhibitor and RNA-directed RNA polymerase inhibitor; and NANPDB2245 as a membrane integrity antagonist. Therefore, they have the potential to inhibit viral entry and replication. These drug-like molecules were predicted to possess attractive pharmacological profiles with negligible toxicity. Novel critical residues identified for both targets could aid in a better understanding of the binding mechanisms and design of fragment-based de novo inhibitors. The compounds are proposed as worthy of further in vitro assaying and as scaffolds for the development of novel SARS-CoV-2 therapeutic molecules.

A novel hydroxyapatite [HAp: Ca 10 (PO 4) 6 (OH) 2 ] material for defluoridation was prepared from Achatina achatina (AA) snail shells using a modified chemical precipitation method. X-ray diffractometry and atomic absorption spectrometry revealed carbonate substitution as a function of stirring conditions. Stirring time was varied to control crystallite size and trace element concentrations. In addition, Infrared spectra, cyclic voltammograms, and ion exchange profiles confirmed the functional groups, the surface mass concentration and the fluoride removal efficiency, respectively. It was observed that the samples prepared after 1 hr optimal stirring times reduced fluoride concentration from 20:00 to 1:59 AE 0:06mgL À1 without affecting the overall pH conditions of the water, whereas beyond this time frame, low uptake of the fluoride ions was obtained with increasing pH conditions. It was also observed that crystallite size did not affect the removal capacity of the samples. The results demonstrated herein the possibility of using locally prepared AA shells for water purification and other environmental remediation applications.

Evidence-based research had shown that elevated alkali treatment of pineapple leaf fiber (PALF) compromised the mechanical properties of the fiber. In this work, PALF was subjected to differential alkali concentrations: 1, 3, 6, and 9% wt/wt to study the influence on the mechanical and crystal properties of the fiber. The crystalline and mechanical properties of untreated and alkali-treated PALF samples were investigated by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and tensile testing analysis. The XRD results indicated that crystal properties of the fibers were modified with 6% wt/wt alkali-treated PALF recording the highest crystallinity and crystallite size of 76% and 24 nm, respectively. The FTIR spectra suggested that all alkali-treated PALF samples underwent lignin and hemicellulose removal to varying degrees. An increase in the crystalline properties improved the mechanical properties of the PALF treated with alkali at 6% wt/wt, which has the highest tensile strength (1620 MPa). Although the elevated alkali treatment resulted in decreased mechanical properties of PALF, crystallinity generally increased. The findings revealed that the mechanical properties of PALF not only improve with increasing crystallinity and crystallite size, but are also dependent on the intermediate bond between adjacent cellulose chains.