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Bitter taste is sensed by bitter taste receptors (TAS2Rs) that belong to the G protein-coupled receptor (GPCR) superfamily. In addition to bitter taste perception, TAS2Rs have been reported recently to be expressed in many extraoral tissues and are now known to be involved in health and disease. Despite important roles of TAS2Rs in biological functions and diseases, no crystal structure is available to help understand the signal transduction mechanism or to help develop selective ligands as new therapeutic targets. We report here the three-dimensional structure of the fully activated TAS2R4 human bitter taste receptor predicted using the GEnSeMBLE complete sampling method. This TAS2R4 structure is coupled to the gustducin G protein and to each of several agonists. We find that the G protein couples to TAS2R4 by forming strong salt bridges to each of the three intracellular loops, orienting the activated Gα5 helix of the Gα subunit to interact extensively with the cytoplasmic region of the activated receptor. We find that the TAS2Rs exhibit unique motifs distinct from typical Class A GPCRs, leading to a distinct activation mechanism and a less stable inactive state. This fully activated bitter taste receptor complex structure provides insight into the signal transduction mechanism and into ligand binding to TAS2Rs.
The preparation of transmission electron microscopy (TEM) samples from powders is quite difficult and challenging. For powders with particles in the 1–5 μm size range, it is especially difficult to select an adequate sample preparation technique. Epoxy is commonly used to bind powder, but drawbacks, such as differential milling originating from unequal milling rates between the epoxy and powder, remain. We propose a new, simple method for preparing TEM samples. This method is especially useful for powders with particles in the 1–5 μm size range that are vulnerable to oxidation. The method uses solder as an embedding agent together with focused ion beam (FIB) milling. The powder was embedded in low-temperature solder using a conventional hot-mounting instrument. Subsequently, FIB was used to fabricate thin TEM samples via the lift-out technique. The solder proved to be more effective than epoxy in producing thin TEM samples with large areas. The problem of differential milling was mitigated, and the solder binder was more stable than epoxy under an electron beam. This methodology can be applied for preparing TEM samples from various powders that are either vulnerable to oxidation or composed of high atomic number elements.
In this study, we synthesized ZnO nanowires using Au catalytic particles formed on a ZnO seed layer. We modulated the microstructure of the ZnO seed layer by changing the sputtering power to investigate how the underlying ZnO film microstructure affects the distribution of ZnO nanowires. Examining the samples after each of the three key steps of the growth process (ZnO seed layer deposition, Au catalytic particle formation, and nanowire growth) using various characterization methods such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction helped us illuminate the profound impacts of the grain size of the seed layer on the nanowire density.
The activation of PPARγ by ligands, including conjugated linoleic acid (CLA) isomers, plays an important role in the immune response. Among CLA isomers, trans-10, cis-12 (t10c12)-CLA is known to participate in the modulation of pro-inflammatory cytokine secretion. The aim of the present study was to assess the effect of t10c12-CLA on PPARγ activation, NF-κB activation and TNF-α expression in lipopolysaccharide (LPS)-naive and LPS-stimulated porcine peripheral blood mononuclear cells (PBMC). In addition, the effect of PPARγ inhibition on NF-κB activation and TNF-α expression in porcine PBMC was examined. t10c12-CLA was found to increase TNF-α expression and NF-κB activity in LPS-naive porcine PBMC. In contrast, t10c12-CLA decreased TNF-α expression and NF-κB activity in LPS-stimulated porcine PBMC. t10c12-CLA up-regulated PPARγ activity and mRNA expression in both LPS-naive and LPS-stimulated porcine PBMC. GW9662, a PPARγ antagonist, completely negated the modulating effects of t10c12-CLA on TNF-α expression and NF-κB activity in both LPS-naive and LPS-stimulated porcine PBMC. These results suggest that t10c12-CLA can modulate TNF-α production and NF-κB activation by a PPARγ-dependent pathway in porcine PBMC.
To investigate the epidemiologic characteristics of vancomycin-resistant enterococci (VRE) infection.
An epidemiologic description by means of chromosomal DNA fingerprinting and transposon typing.
A 2,200-bed tertiary care hospital in Korea.
First VRE isolates were obtained from patients hospitalized from April 1997 to December 2001.
The van genotypes of isolates were identified by means of multiplex polymerase chain reaction (PCR). The macro-restriction patterns of chromosomal DNA were determined by pulsed-field gel electrophoresis (PFGE). The transposon Tn1546was typed by means of 2 sets of long PCR restriction fragment-length polymorphism analysis, which were ClaI restriction of a 10.4-kb region from orf1 to vanZ and DdeI restriction of a 4.4-kb region from vanR to vanX.
VRE isolates were recovered from 215 patients. All were vanA genotype. PFGE analysis of the 215 isolates showed 172 types, including 21 clusters composed of 64 isolates and 151 types of as many isolates. Each type was composed of 2-10 isolates; the isolates within each PFGE cluster were detected within a 10-month period and mostly shared a transposon type. Transposon typing classified 169 strains into 15 types and 158 strains belonged to 4 major transposon clusters. Each of these 4 transposon clusters was isolated from patients treated in 5-22 different wards during a 31-52 month period and consisted of 9-80 PFGE types. Each of the other 11 types were found in only one strain.
Our findings suggest that the horizontal transfer of Tn1546 has a major role in the nosocomial spread of vanA VRE. Clonal spread of VRE seemed to contribute to short-term dissemination in limited areas.
SiC nanowire was grown by APCVD using single precursors. Grown SiC nanowires had 10∼60nm diameters and lengths of several micrometers. Nanowire's diameters and lengths were varied with kind of catalysts. Nanowire's growth scheme was divided by two regions with diameter of nanowire. At first region, nanowire was grown by VLS (vapor-liquid-solid) mechanism, but at the second region, nanowire growth was made by VS (vapor-solid) reaction. These differences were made from limitations of growth rate and deactivation effects. Growth temperature, time and flow rates of source gases were affected nanowire's diametesr and its lengths. And kind of catalysts, coating methods and precursors were affected growth direction and microstructures too.
SiOx nanowire were synthesized using VLS (vapor-liquid-solid) and SLS (ssolid-liquid-solid) growth mechanism. Grown nanowires had a different shapes by the kind of substrates and kind of catalysts. Diameters and lengths of grown nanowires were varied with growth conditions. By vapor evaporation method, used substrates effected growth scheme and density of nanowires because of differences of catalyst nucleation characteristics. Grown nanowires showed different microstructures and optical properties. By catalyst evaporation method, various shapes of SiOx nanowires were grown. These shapes of nanowire were formed by the typical reaction of catalyst and Si source. Measured optical properties show blue luminescence about 430nm because of oxygen defects in the nannowire.
To evaluate the outcome of attempted Hickman catheter salvage in neutropenic cancer patients with Staphylococcus aureus bacteremia who were not using antibiotic lock therapy.
Retrospective cohort study.
A university-affiliated, tertiary-care hospital with 1,500 beds for adult patients.
All neutropenic cancer patients who had a Hickman catheter and S. aureus bacteremia (32 episodes in 29 patients) between January 1998 and March 2002.
Salvage attempts were defined as cases where the Hickman catheter was not removed until we obtained the results of follow-up blood cultures performed 48 to 72 hours after starting treatment with antistaphylococcal antibiotics. Salvage was considered to be successful if the Hickman catheter was still in place 3 months later without recurrent bacteremia or death.
Catheter salvage was attempted in 24 (75%) of the 32 episodes. Of the salvage attempts, the success rate was 50% (12 of 24). Salvage attempts were successful in 14% (1 of 7) of the episodes with positive follow-up blood cultures, and in 65% (11 of 17) of those with negative follow-up blood cultures (P = .07). If the analysis is confined to cases with no external signs of catheter infection, salvage attempts were successful in 14% (1 of 7) of the episodes with positive follow-up blood cultures and in 80% (8 of 10) of those with negative follow-up blood cultures (P = .02).
In neutropenic cancer patients with S. aureus bacteremia, attempted catheter salvage without antibiotic lock therapy was successful in 50% of the cases.
To identify antibiotic resistance trends and risk factors for resistance of Serratia species to third-generation cephalosporins.
Retrospective survey of medical records.
A 2,200-bed, tertiary-care hospital.
One hundred twenty-two patients with Serratia bacteremia between January 1991 and June 2001.
Infectious disease physicians collected data from medical records regarding patient demographics, underlying disease or condition, portal of entry, microorganism, antibiogram, complications, antibiotics received, and outcome.
Among 122 Serratia isolates, 117 (95.9%) were Serratia marcescens and 110 (90.2%) were of nosocomial origin. During the study period, the 122 isolates showed a high rate of resistance to third-generation cephalosporins (45.9%) and extended-spectrum penicillins (56.6%). The resistance rate to ciprofloxacin was 32.0%. The resistance rate to third-generation cephalosporins increased from 31.7% for 1991 to 1995 to 54.9% for 1996 to 1998 and 50.0% for 1999 to 2001. In the multivariate analysis, prior use of a second-generation cephalosporin (adjusted odds ratio [OR], 5.90; 95% confidence interval [CI95], 1.41 to 24.6; P = .015) or a third-generation cephalosporin (OR, 3.26; CI95, 1.20 to 8.87; P = .020) was a strong independent risk factor for resistance to third-generation cephalosporins. The overall case-fatality rate was 25.4% (Serratia bacteremia-related case-fatality rate, 13.1%).
Prior use of a second- or third-generation cephalosporin was the most important risk factor for bacteremia with Serratia resistant to third-generation cephalosporins, suggesting the need for antibiotic control. The potential role of patient-to-patient spread could not be fully evaluated in this retrospective study.
Bulk-quantity single crystalline wurtzite gallium nitride nanowires with a mean diameter of 25 nm were synthesized on silicon substrate using a catalyst-assisted reaction of gallium and gallium nitride mixture with ammonia. They exhibit a strong and broad photoluminescence in the energy range of 2.9-3.6 eV with no yellow band. X-ray diffraction and Raman scattering data suggest that the nanowires would experience biaxial compressive stresses in the inward radial direction and the induced tensile uniaxial stresses in the wire axis. The blue photoluminescence would originate from the recombination of the bound excitons under the compressive and tensile stresses.
Interfacial reactions between an Al thin film and a single-crystal (001) 6H–SiC substrate were investigated using x-ray diffraction and cross-sectional transmission electron microscopy. Aluminum thin films were prepared by radio-frequency magnetron sputtering method on 6H–SiC substrates at room temperature and then annealed at various temperatures from 500 to 900 °C. A columnar-type polycrystalline Al thin film was formed on a 6H–SiC substrate in the as-deposited sample. No remarkable microstructural change, compared to the as-deposited sample, was observed in the sample annealed at 500 °C for 1 h. However, it was found that the Al layer reacted with the SiC substrate at 700 °C and formed an Al–Si–C ternary compound at the Al/SiC interface. Samples annealed at 900 °C showed a double-layer structure with an Al–Si mixed surface layer and an Al–Si–C compound layer below in contact with the substrate.
High quality ZnS epilayers were grown on GaAs and GaP substrates by hot wall epitaxy. The optimum temperature conditions for high quality ZnS epilayer were found. The photoluminescence(PL) spectrum of high quality ZnS epilayers showed sharp and narrow exciton peaks and no self-activated peaks. The room temperature energy gap of ZnS/GaAs was found to be 3.729 eV from the experimentally observed free exciton PL peaks. The temperature dependence of the PL intensity showed a two step quenching process and the temperature dependence of the PL linewidth broadening was tried to analyze in terms of exciton scattering process. From the splitting of the heavy hole and the light hole exciton peaks, the strain was identified.
A gradual change in thermal oxide surface state from hydrophilic to hydrophobic was observed with time -delay in a clean room environment. Surface quality and reflectivity for the Al/Ti metal layers showed a strong dependency on the oxide surface state. From the hydrophilic oxide substrate, a lower (002) Ti preferred orientation was obtained than from hydrophobic ones. This resulted in a degraded (111) Al preferred orientation and rough metal surface. The RF-etch process increased the smoothness and hydrophobic surface property for the inter -metal dielectric (IMD) oxides, and therefore greatly improved Al/Ti surface quality. When conventional CMOS double layer metal interconnection process is performed, metal inter-line bridge yield was strongly affected by the surface state of substrate oxides.
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