1,748 research outputs found
Chemically engineering ligand selectivity at the free fatty acid receptor 2 based on pharmacological variation between species orthologs
When it is difficult to develop selective ligands within a family of related G-protein-coupled receptors (GPCRs), chemically engineered receptors activated solely by synthetic ligands (RASSLs) are useful alternatives for probing receptor function. In the present work, we explored whether a RASSL of the free fatty acid receptor 2 (FFA2) could be developed on the basis of pharmacological variation between species orthologs. For this, bovine FFA2 was characterized, revealing distinct ligand selectivity compared with human FFA2. Homology modeling and mutational analysis demonstrated a single mutation in human FFA2 of C4.57G resulted in a human FFA2 receptor with ligand selectivity similar to the bovine receptor. This was exploited to generate human FFA2-RASSL by the addition of a second mutation at a known orthosteric ligand interaction site, H6.55Q. The resulting FFA2-RASSL displayed a >100-fold loss of activity to endogenous ligands, while responding to the distinct ligand sorbic acid with pEC(50) values for inhibition of cAMP, 5.83 ± 0.11; Ca(2+) mobilization, 4.63 ± 0.05; ERK phosphorylation, 5.61 ± 0.06; and dynamic mass redistribution, 5.35 ± 0.06. This FFA2-RASSL will be useful in future studies on this receptor and demonstrates that exploitation of pharmacological variation between species orthologs is a powerful method to generate novel chemically engineered GPCRs
Optical properties of arrays of quantum dots with internal disorder
Optical properties of large arrays of isolated quantum dots are discussed in
order to interpret the existent photoluminescence data. The presented theory
explains the large observed shift between the lowest emission and absorption
energies as the average distance between the ground and first excited states of
the dots. The lineshape of the spectra is calculated for the case when the
fluctuations of the energy levels in quantum dots are due to the alloy
composition fluctuations. The calculated lineshape is in good agreement with
the experimental data. The influence of fluctuations of the shape of quantum
dots on the photoluminescence spectra is also discussed.Comment: 7 pages (twocolumn) LATEX, 6 Postscript figure
Self-consistent Coulomb effects and charge distribution of quantum dot arrays
This paper considers the self-consistent Coulomb interaction within arrays of
self-assembled InAs quantum dots (QDs) which are embedded in a pn structure.
Strong emphasis is being put on the statistical occupation of the electronic QD
states which has to be solved self-consistently with the actual
three-dimensional potential distribution. A model which is based on a Green's
function formalism including screening effects is used to calculate the
interaction of QD carriers within an array of QDs, where screening due to the
inhomogeneous bulk charge distribution is taken into acount. We apply our model
to simulate capacitance-voltage (CV) characteristics of a pn structure with
embedded QDs. Different size distributions of QDs and ensembles of spatially
perodic and randomly distributed arrays of QDs are investigated.Comment: submitted to pr
Effect of deconfinement on resonant transport in quantum wires
The effect of deconfinement due to finite band offsets on transport through
quantum wires with two constrictions is investigated. It is shown that the
increase in resonance linewidth becomes increasingly important as the size is
reduced and ultimately places an upper limit on the energy (temperature) scale
for which resonances may be observed.Comment: 6 pages, 6 postscript files with figures; uses REVTe
Hot-phonon effects in photo-excited wide-bandgap semiconductors
Carrier and lattice relaxation after optical excitation is simulated for the prototypical
wide-bandgap semiconductors CuI and ZnO. Transient temperature dynamics of electrons,
holes as well as longitudinal-optic (LO), transverse-optic (TO) and acoustic phonons are
distinguished. Carrier-LO-phonon interaction constitutes the dominant energy-loss channel as
expected for polar semiconductors and hot-phonon effects are observed for strong optical
excitation. Our results support the findings of recent time-resolved optical spectroscopy
experiments
Influence of symmetry and Coulomb-correlation effects on the optical properties of nitride quantum dots
The electronic and optical properties of self-assembled InN/GaN quantum dots
(QDs) are investigated by means of a tight-binding model combined with
configuration interaction calculations. Tight-binding single particle wave
functions are used as a basis for computing Coulomb and dipole matrix elements.
Within this framework, we analyze multi-exciton emission spectra for two
different sizes of a lens-shaped InN/GaN QD with wurtzite crystal structure.
The impact of the symmetry of the involved electron and hole one-particle
states on the optical spectra is discussed in detail. Furthermore we show how
the characteristic features of the spectra can be interpreted using a
simplified Hamiltonian which provides analytical results for the interacting
multi-exciton complexes. We predict a vanishing exciton and biexciton ground
state emission for small lens-shaped InN/GaN QDs. For larger systems we report
a bright ground state emission but with drastically reduced oscillator
strengths caused by the quantum confined Stark effect.Comment: 15 pages, 17 figure
Absence of Nucleotide-Oligomerization-Domain-2 Is Associated with Less Distinct Disease in Campylobacter jejuni Infected Secondary Abiotic IL-10 Deficient Mice
Human Campylobacter jejuni-infections are progressively increasing worldwide.
Despite their high prevalence and socioeconomic impact the underlying
mechanisms of pathogen-host-interactions are only incompletely understood.
Given that the innate immune receptor nucleotide-oligomerization-domain-2
(Nod2) is involved in clearance of enteropathogens, we here evaluated its role
in murine campylobacteriosis. To address this, we applied Nod2-deficient
IL-10−/− (Nod2−/− IL-10−/−) mice and IL-10−/− counterparts both with a
depleted intestinal microbiota to warrant pathogen-induced enterocolitis. At
day 7 following peroral C. jejuni strain 81–176 infection, Nod2 mRNA was down-
regulated in the colon of secondary abiotic IL-10−/− and wildtype mice.
Nod2-deficiency did neither affect gastrointestinal colonization nor extra-
intestinal and systemic translocation properties of C. jejuni. Colonic mucin-2
mRNA was, however, down-regulated upon C. jejuni-infection of both Nod2−/−
IL-10−/− and IL-10−/− mice, whereas expression levels were lower in infected,
but also naive Nod2−/− IL-10−/− mice as compared to respective IL-10−/−
controls. Remarkably, C. jejuni-infected Nod2−/− IL-10−/− mice were less
compromised than IL-10−/− counterparts and displayed less distinct apoptotic,
but higher regenerative cell responses in colonic epithelia. Conversely,
innate as well as adaptive immune cells such as macrophages and monocytes as
well as T lymphocytes and regulatory T-cells, respectively, were even more
abundant in large intestines of Nod2−/− IL-10−/− as compared to IL-10−/− mice
at day 7 post-infection. Furthermore, IFN-γ concentrations were higher in ex
vivo biopsies derived from intestinal compartments including colon and
mesenteric lymph nodes as well as in systemic tissue sites such as the spleen
of C. jejuni infected Nod2−/− IL-10−/− as compared to IL10−/− counterparts.
Whereas, at day 7 postinfection anti-inflammatory IL-22 mRNA levels were up-
regulated, IL-18 mRNA was down-regulated in large intestines of Nod2−/−
IL-10−/− vs. IL-10−/− mice. In summary, C. jejuni-infection induced less
clinical signs and apoptosis, but more distinct colonic pro- and (of note)
anti-inflammatory immune as well as regenerative cell responses in Nod2
deficient IL-10−/− as compared to IL-10−/− control mice. We conclude that,
even though colonic Nod2 mRNA was down-regulated upon pathogenic challenge,
Nod2-signaling is essentially involved in the well-balanced innate and
adaptive immune responses upon C. jejuni-infection of secondary abiotic
IL-10−/− mice, but does neither impact pathogenic colonization nor
translocation
Campylobacter jejuni infection of conventionally colonized mice lacking nucleotide-oligomerization-domain-2
Background The nucleotide-binding oligomerisaton protein 2 (NOD2) constitutes
a pivotal sensor of bacterial muramyl dipeptide and assures expression of
distinct antimicrobial peptides and mediators produced by enterocytes and
immune cells directed against pathogens including Campylobacter jejuni. We
here elucidated the role of NOD2 during murine C. jejuni infection in more
detail. Results Conventionally colonized NOD2 deficient (NOD2−/−) mice and
corresponding wildtype (WT) counterparts were perorally infected with C.
jejuni strain 81–176 on three consecutive days. The pathogen colonized both WT
and NOD2−/− mice only sporadically until day 14 post infection (p.i.).
However, the slightly higher prevalence of C. jejuni in NOD2−/− mice was
accompanied by higher intestinal Escherichia coli loads known to facilitate C.
jejuni colonization. Neither overt macroscopic (clinical) nor microscopic
sequelae (such as colonic epithelial apoptosis) could be observed upon murine
C. jejuni infection of either genotype. Innate immune responses were less
distinctly induced in C. jejuni infected NOD2−/− versus WT mice as indicated
by lower colonic numbers of neutrophils in the former. Conversely, adaptive
immune cell counts including T lymphocytes were higher in large intestines of
NOD2−/− as compared to WT mice that were paralleled by increased colonic IL-6
secretion and higher TNF and IL-18 mRNA expression levels in large intestines
of the former. Only in NOD2−/− mice, however, colonic IL-22 mRNA expression
was down-regulated at day 14 p.i. Whereas viable commensal intestinal bacteria
could exclusively be detected in mesenteric lymph nodes and livers of NOD2−/−
mice, bacterial translocation rates to kidneys and spleen were NOD2
independent. Notably, large intestinal mRNA expression levels of mucin-2,
constituting a pivotal factor involved in epithelial barrier integrity, were
comparable in naive and C. jejuni infected mice of either genotype. Conclusion
NOD2 is involved in the well-balanced regulation of innate and adaptive pro-
inflammatory immune responses of conventional mice upon C. jejuni infection
- …