Solution-State 2D NMR Spectroscopy of Plant Cell Walls Enabled by a Dimethylsulfoxide‑<i>d</i>₆/1-Ethyl-3-methylimidazolium Acetate Solvent

Lignocellulosic biomass is composed of the polysaccharides cellulose and hemicellulose and the polyphenol lignin. Many current methods for analyzing the structure of lignocelluloses involve a sequential extraction of the material and subsequent analysis of the resulting fractions, which is labor-intensive and time-consuming. The work presented here assesses the dissolution of whole lignocellulosic material, focusing on biomass derived from the perennial bioenergy grass <i>Miscanthus</i>. The solvent dimethylsulfoxide (DMSO)-<i>d</i>₆ containing 1-ethyl-3-methylimidazolium acetate ([Emim]­OAc) was able to dissolve lignocellulosic material completely and gave high-resolution 2D heteronuclear single quantum coherence (HSQC) NMR spectra of the entire array of wall polymers. Extrapolated time-zero HSQC was applied using DMSO-<i>d</i>₆/[Emim]­OAc-<i>d</i>₁₄ and enabled quantitative analysis of structural traits of lignocellulose components

Schematic illustration of microscale reaction of NTPDases at capillary inlet

<p><b>Copyright information:</b></p><p>Taken from "A capillary electrophoresis method for the characterization of ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) and the analysis of inhibitors by in-capillary enzymatic microreaction"</p><p></p><p>Purinergic Signalling 2005;1(4):349-358.</p><p>Published online Jan 2005</p><p>PMCID:PMC2096555.</p><p></p> 1. Injection of a sample of 4 nl of 320 µM of ATP (substrate) in reaction buffer containing UMP (20 µM) as an internal standard in the absence or presence of test compound (potential inhibitors) (0.3 p.s.i., 5 s); 2. Injection of enzyme (0.3 p.s.i., 5 s); 3. Injection of 320 µM of ATP (substrate) in reaction buffer containing UMP (20 µM) as an internal standard in the absence or presence of test compound (0.3 p.s.i., 5 s); 4. Overlayed plugs are then allowed to stand during a predetermined period of 5 min; 5. Subsequently a −60 µA current is applied and the reaction products migrate to the detector. Electrophoresis conditions were as described in the experimental section

Overlay of five electropherograms after NTPDase3 on-line reaction at the capillary inlet with different concentrations of reactive blue 2 (inhibitor) added to the substrate plug

<p><b>Copyright information:</b></p><p>Taken from "A capillary electrophoresis method for the characterization of ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) and the analysis of inhibitors by in-capillary enzymatic microreaction"</p><p></p><p>Purinergic Signalling 2005;1(4):349-358.</p><p>Published online Jan 2005</p><p>PMCID:PMC2096555.</p><p></p> The concentration of NTPDase3 was 0.05 µg/µl of protein, ATP: 320 µM, UMP (internal standard): 40 µM. Waiting period (duration of enzymatic reaction): 5.0 min. CE conditions: Running buffer: 50 mM potassium phosphate, pH 6.5; constant current of −60 µA; detection at 210 nm, capillary cartridge temperature: 37 °C. Reactive blue 2 (RB2) concentrations: a) 20, b) 6, c) 2, d) 0.6 and e) 0.2 µM. The lowest concentration (0.2 µM) gave virtually the same electropherogram as the control without inhibitor

Investigation of Model Membrane Disruption Mechanism by Melittin using Pulse Electron Paramagnetic Resonance Spectroscopy and Cryogenic Transmission Electron Microscopy

Studies of membrane peptide interactions at the molecular level are important for understanding essential processes such as membrane disruption or fusion by membrane active peptides. In a previous study, we combined several electron paramagnetic resonance (EPR) techniques, particularly continuous wave (CW) EPR, electron spin echo envelope modulation (ESEEM), and double electron–electron resonance (DEER) with Monte Carlo (MC) simulations to probe the conformation, insertion depth, and orientation with respect to the membrane of the membrane active peptide melittin. Here, we combined these EPR techniques with cryogenic transmission electron microscopy (cryo-TEM) to examine the effect of the peptide/phospholipid (P/PL) molar ratio, in the range of 1:400 to 1:25, on the membrane shape, lipids packing, and peptide orientation and penetration. Large unilamellar vesicles (LUVs) of DPPC/PG (7:3 dipalmitoylphosphatidylcholine/egg phosphatidylglycerol) were used as model membranes. Spin-labeled peptides were used to probe the peptide behavior whereas spin-labeled phspholipids were used to examine the membrane properties. The cryo-TEM results showed that melittin causes vesicle rupture and fusion into new vesicles with ill-defined structures. This new state was investigated by the EPR methods. In terms of the peptide, CW EPR showed decreased mobility, and ESEEM revealed increased insertion depth as the P/PL ratio was raised. DEER measurements did not reveal specific aggregates of melittin, thus excluding the presence of stable, well-defined pore structures. In terms of membrane properties, the CW EPR reported reduced mobility in both polar head and alkyl chain regions with increasing P/PL. ESEEM measurements showed that, as the P/PL ratio increased, a small increase in water content in the PL headgroup region took place and no change was observed in the alkyl chains part close to the hydrophilic region. In terms of lipid local density, opposite behavior was observed for the polar head and alkyl chain regions with increasing P/PL; while the DPPC density increased in the polar head region, it decreased in the alkyl chain region. These results are consistent with disruption of the lipid order and segregation of the PL constituents of the membrane as a consequence of the melittin binding. This work further demonstrates the applicability and potential of pulse EPR techniques for the study of peptide–membrane interactions

Virtual Screening Identifies Novel Sulfonamide Inhibitors of <i>ecto</i>-5′-Nucleotidase

We aimed to identify inhibitors of <i>ecto</i>-5′-nucleotidase (<i>ecto</i>-5′-NT, CD73), a membrane-bound metallophosphoesterase that is implicated in the control of purinergic receptor signaling and a number of associated therapeutically relevant effects. Currently, only very few compounds, including ADP, its more stable analogue α,β-methylene-ADP, ATP, and anthraquinone derivatives are known to inhibit this enzyme. In the search for inhibitors with more drug-like properties, we applied a model structure-based virtual screening approach augmented by chemical similarity searching. On the basis of this analysis, 51 candidate compounds were finally selected for experimental evaluation. A total of 13 of these molecules were confirmed to have competitive inhibitory activity. The most potent inhibitor, 6-chloro-2-oxo-<i>N</i>-(4-sulfamoylphenyl)-2<i>H</i>-chromene-3-carboxylic acid amide (<b>17</b>), showed an IC₅₀ value of 1.90 μM. In contrast to the nucleotide- and anthraquinone-derived antagonists, the newly identified competitive inhibitors are uncharged at physiological pH values, possess a drug-like structure, and are structurally distinct from known active compounds

Correction to Thiolate Spin Population of Type I Copper in Azurin Derived from ³³S Hyperfine Coupling

Correction to Thiolate Spin Population of Type I Copper in Azurin Derived from ³³S Hyperfine Couplin

α,β-Methylene-ADP (AOPCP) Derivatives and Analogues: Development of Potent and Selective <i>ecto</i>-5′-Nucleotidase (CD73) Inhibitors

<i>ecto</i>-5′-Nucleotidase (<i>e</i>N, CD73) catalyzes the hydrolysis of extracellular AMP to adenosine. <i>e</i>N inhibitors have potential for use as cancer therapeutics. The <i>e</i>N inhibitor α,β-methylene-ADP (AOPCP, adenosine-5′-<i>O</i>-[(phosphonomethyl)­phosphonic acid]) was used as a lead structure, and derivatives modified in various positions were prepared. Products were tested at rat recombinant <i>e</i>N. 6-(Ar)­alkylamino substitution led to the largest improvement in potency. <i>N</i>⁶-Monosubstitution was superior to symmetrical <i>N</i>⁶,<i>N</i>⁶-disubstitution. The most potent inhibitors were <i>N</i>⁶-(4-chlorobenzyl)- (<b>10l</b>, PSB-12441, <i>K</i>_i 7.23 nM), <i>N</i>⁶-phenylethyl- (<b>10h</b>, PSB-12425, <i>K</i>_i 8.04 nM), and <i>N</i>⁶-benzyl-adenosine-5′-<i>O</i>-[(phosphonomethyl)­phosphonic acid] (<b>10g</b>, PSB-12379, <i>K</i>_i 9.03 nM). Replacement of the 6-NH group in <b>10g</b> by O (<b>10q</b>, PSB-12431) or S (<b>10r</b>, PSB-12553) yielded equally potent inhibitors (<b>10q</b>, 9.20 nM; <b>10r</b>, 9.50 nM). Selected compounds investigated at the human enzyme did not show species differences; they displayed high selectivity versus other <i>ecto</i>-nucleotidases and ADP-activated P2Y receptors. Moreover, high metabolic stability was observed. These compounds represent the most potent <i>e</i>N inhibitors described to date