Cellular inhibition of protein tyrosine phosphatase 1B by uncharged thioxothiazolidinone derivatives

As important regulators of cellular signal transduction, members of the protein tyrosine phosphatase (PTP) family are considered to be promising drug targets. However, to date, the most effective in vitro PTP inhibitors have tended to be highly charged, thus limiting cellular permeability. Here, we have identified an uncharged thioxothiazolidinone derivative (compound 1), as a competitive inhibitor of a subset of PTPs. Compound 1 effectively inhibited protein tyrosine phosphatase 1B (PTP1B) in two cell-based systems: it sensitized wild-type, but not PTP1B-null fibroblasts to insulin stimulation and prevented PTP1B-dependent dephosphorylation of the FLT3-ITD receptor tyrosine kinase. We have also tested a series of derivatives in vitro against PTP1B and proposed a model of the PTP1B-inhibitor interaction. These compounds should be useful in the elucidation of cellular PTP function and could represent a starting point for development of therapeutic PTP inhibitors.     

Structural analysis of the capsular polysaccharide from Campylobacter jejuni RM1221

The complete genome of Campylobacter jejuni strain RM1221 (Penner serotype HS:53) was reported recently and contains a novel capsular polysaccharide (CPS) biosynthesis locus. Cell-surface carbohydrates such as CPS are known to be important for bacterial survival and often contribute to pathogenesis. In this study, we describe the complete structure of the CPS of C. jejuni RM1221, which was determined by using NMR spectroscopy, MS, and chemical methods. The CPS contains 6-deoxy-D-manno-heptose and D-threo-pent-2-ulose (D-xylulose), two monosaccharides that are rarely found in bacterial polysaccharides. The CPS has a regular structure of a linear main chain of trisaccharide repeating units, composed of two alpha- and one beta-6-deoxy-D-manno-heptopyranose residues, which are linked through a phosphodiester linkage. Branching residues of xylulose are incorporated nonstoichiometrically: each trisaccharide repeating unit of the main chain bears no, one, or two xylulose residues. The xylulose glycosidic linkages are extremely acid labile, and it is not clear how they can be preserved under the acidic conditions of the gastrointestinal tract, where Campylobacter resides during infection. We have also shown that the CPS biosynthesis genes of C. jejuni RM1221 are conserved in other C. jejuni strains of the Penner serotype HS:53, including serotype HS:53 reference strain RM3435.     

A fluorogenic peptide containing the processing site of human SARS corona virus S-protein: kinetic evaluation and NMR structure elucidation

Human severe acute respiratory syndrome coronavirus (hSARS-CoV) is the causative agent for SARS infection. Its surface glycoprotein (spike protein) is considered to be one of the prime targets for SARS therapeutics and intervention because its proteolytic maturation by a host protease is crucial for host-virus fusion. Using intramolecularly quenched fluorogenic (IQF) peptides based on hSARS-CoV spike protein (Abz-(755)Glu-Gln-Asp-Arg-Asn-Thr-Arg-Glu-Val-Phe-Ala-Gln(766)-Tyx-NH(2)) and in vitro studies, we show that besides furin, other PCs, like PC5 and PC7, might also be involved in this cleavage event. Through kinetic measurements with recombinant PCs, we observed that the peptide was cleaved efficiently by both furin and PC5, but very poorly by PC7. The cleavage could be blocked by a PC-inhibitor, alpha1-PDX, in a dose-dependent manner. Circular dichroism spectra indicated that this peptide possesses a high degree of sheet structure. Following cleavage by furin, the sheet content increased, possibly at the expense of turn and random structures. (1)H NMR spectra from 2D COSY and ROESY experiments under physiological buffer and pH conditions indicated that this peptide possesses a structure with a turn at its C-terminal segment, close to the cleavage site. The data suggest that the cleavable peptide bond is located within the most exposed domain; this is supported by the nearby turn structure. Several strong to weak NMR ROESY correlations were detected, and a 3D structure of the spike IQF peptide that contains the crucial cleavage site R(761) E has been proposed.     

Four-week short chain fructo-oligosaccharides ingestion leads to increasing fecal bifidobacteria and cholesterol excretion in healthy elderly volunteers

Background  

Short-chain fructo-oligosaccharides (scFOS) are increasingly used in human diet for their prebiotic properties. We aimed at investigating the effects of scFOS ingestion on the colonic microflora and oro-fecal transit time in elderly healthy humans.     

Electrochemistry at capped platinum nanoparticle Langmuir Blodgett films: A study of the influence of platinum amount and of number of LB layers

Platinum nanoparticles (n-Pt), over-grafted with 2-thiophenecarbonyl chloride are assembled on gold electrodes, by the Langmuir Blodgett (LB) technique using behenic acid (BHA) as promoting agent. These layers are electrochemically active without any preliminary activation. The [Fe(CN)₆]^3−/4− redox couple was used as electrochemical probe. This paper reports on the influence of the number of deposited LB layers, and the n-Pt density on the electrochemical response. n-Pt density was modified by the change of the “BHA/n-Pt” ratio. Cyclic voltammograms of “[Fe(CN)₆]^3−/4−” were observed whatever the coating conditions. As soon as the first layer was deposited the electrochemical response was associated to the n-Pt coverage, its response slightly increased up to a steady state for five or seven layers. As expected, the increase of the Pt density favored the increase of the current density. XPS analysis performed before and after electrochemical cycling showed that 4-mercaptoaniline capped platinum nanoparticles, and their over grafting were chemically and electrochemically stable. Analysis of influence of the number or the n-Pt density of the layers showed that the electrochemically active part of LB electrodes was provided by the last layer plus a part of the underlying one.     

Membrane phospholipids and sterols in microfiltered milk fat globules

Native milk fat globules of various mean diameters, ranging from d₄₃ = 2.3 µm to 8.0 µm, were obtained using microfiltration of raw whole milk. After milk fat globule washing, the milk fat globule membrane (MFGM) was separated by manual churning. After total lipid extraction and separation of polar lipids, their phospholipid (PL) and sterol composition was measured using thin‐layer chromatography, methyl ester analyses by gas chromatography, and gas chromatography coupled to mass spectrometry. The main PL species were phosphatidylethanolamine, phosphatidylcholine and sphingomyelin. The respective fatty acid composition of each PL species was measured. Many different minor bioactive sterols were detected in the MFGM, e.g. lanosterol, lathosterol, desmosterol, stigmasterol and β‐sitosterol. No significant differences in the PL and sterol profile were found between MFGM extracted from small and large milk fat globule fractions.     

Inhibitive properties, adsorption and a theoretical study of 3,5-bis(n-pyridyl)-4-amino-1,2,4-triazoles as corrosion inhibitors for mild steel in perchloric acid

Corrosion inhibition of mild steel in molar perchloric acid by 3,5-bis(n-pyridyl)-4-amino-1,2,4-triazoles (n-PAT, n = 2, 3 and 4) was studied at 30 °C using gravimetric and electrochemical impedance spectroscopy techniques. Protection efficiencies of 95% and 92% were obtained with 12 × 10⁻⁴ M of 3-PAT and 4-PAT, respectively; while 2-PAT reached only 65%. The inhibiting properties of n-PAT were found to depend on the concentration and the order of increasing inhibition efficiency was correlated with the modification of the position of the nitrogen atom in the pyridinium substituent. It was shown that adsorption of 4-aminotriazole derivatives on the steel surface is consistent with the Langmuir adsorption isotherm and the obtained standard free energy of adsorption () values indicate that the corrosion inhibition of the mild steel in 1 M HClO₄ is depends on both physic-and chemisorption. A significant correlation is obtained between inhibition efficiency and quantum chemical parameters using semi-empirical quantitative structure-activity relationships (QSAR) approach.     

Electrophysiological and Behavioral Responses of a Cuban Population of the Sweet Potato Weevil to its Sex Pheromone

The sex pheromone of feral sweet potato weevils Cylas formicarius elegantulus from Cuba was found, via solid-phase microextraction analysis, to be identical to (Z)-3-dodecenyl (E)-2-butenoate, a previously reported compound. Females emitted 20 pg pheromone d⁻¹. In scanning electron microscopy studies carried out on the male antenna, we identified several types of sensilla: sensilla trichoidea of type 1 (ST1) as long hairs (100–150 μm), sensilla trichoidea of type 2 as short hairs (50–60 μm), sensilla basiconica of type 1 as thick pegs (20–25 μm), sensilla basiconica of type 2 as curved pegs (10–15 μm), and sensilla basiconica of type 3 as thin and straight short pegs (15–20 μm). The same types were observed in female antennae but ST1 were far less abundant than in males. Sensilla chaetica were also found on the flagellum subsegments in both sexes. In electrophysiological tests, the crotonate function in the pheromone structure proved to be critical for activity since regular depolarizations (0.6–0.8 mV) were obtained with puffs on 1 μg of the attractant, but not with puffs of the formate, acetate, propionate, or butyrate analogue of the pheromone. In a double dual-choice olfactometer, males showed maximum activity between the 4th and the 8th hr of scotophase at a dose of 50–1000 ng of pheromone. In field tests, a correlation between the contents of the Z,E isomer in the pheromone formulation with activity was noticed, and baits containing this isomer of stereomeric purity >94% showed the highest attractivity. The presence of 5% of the Z,Z isomer in the lure did not induce any synergistic or inhibitory effect, and the alcohol precursor of the pheromone was inactive. The results show that use of a stereomerically pure pheromone may not be necessary in pest control strategies.     

Coexistence in a chemostat: Application of a threshold policy

A well known result in chemostat theory states that two populations of microorganisms which compete for a single limiting nutrient cannot coexist under the condition of a spatially uniform environment and time invariant external influences. In this same setting, altering the dilution rate by means of a threshold policy can revert competitive exclusion to species coexistence in a vicinity of a previously chosen concentration.