4,689 research outputs found
Dissecting the Functions of Conserved Prolines within Transmembrane Helices of the D2 Dopamine Receptor
G protein-coupled receptors (GPCRs) contain a number of conserved proline residues in their transmembrane helices, and it is generally assumed these play important functional and/or structural roles. Here we use unnatural amino acid mutagenesis, employing α-hydroxy acids and proline analogues, to examine the functional roles of five proline residues in the transmembrane helices of the D2 dopamine receptor. The well-known tendency of proline to disrupt helical structure is important at all sites, while we find no evidence for a functional role for backbone amide cisâtrans isomerization, another feature associated with proline. At most proline sites, the loss of the backbone NH is sufficient to explain the role of the proline. However, at one site, P210^(5.50), a substituent on the backbone N appears to be essential for proper function. Interestingly, the pattern in functional consequences that we see is mirrored in the pattern of structural distortions seen in recent GPCR crystal structures
Quasiperpendicular high Mach number Shocks
Shock waves exist throughout the universe and are fundamental to
understanding the nature of collisionless plasmas. Reformation is a process,
driven by microphysics, which typically occurs at high Mach number
supercritical shocks. While ongoing studies have investigated this process
extensively both theoretically and via simulations, their observations remain
few and far between. In this letter we present a study of very high Mach number
shocks in a parameter space that has been poorly explored and we identify
reformation using in situ magnetic field observations from the Cassini
spacecraft at 10 AU. This has given us an insight into quasi-perpendicular
shocks across two orders of magnitude in Alfven Mach number (MA) which could
potentially bridge the gap between modest terrestrial shocks and more exotic
astrophysical shocks. For the first time, we show evidence for cyclic
reformation controlled by specular ion reflection occurring at the predicted
timescale of ~0.3 {\tau}c, where {\tau}c is the ion gyroperiod. In addition, we
experimentally reveal the relationship between reformation and MA and focus on
the magnetic structure of such shocks to further show that for the same MA, a
reforming shock exhibits stronger magnetic field amplification than a shock
that is not reforming.Comment: Accepted and Published in Physical Review Letters (2015
Charge-transfer heptamethine dyes for NIR singlet oxygen generation
A heptamethine-based charge-transfer dye was designed based on previous evidence of triplet state formation in orthogonal charge-transfer partners and calculations suggesting the formation of a charge-transfer state in heptamethine dye derivatives. An acridinium derivative of IR-1061 was subsequently synthesized and characterized, demonstrating photochemical reactivity at wavelengths over 1000 nm
Effects of Substituents on the Length of Central C(sp^3)-C(sp^3) Bond in Anthracene Photodimers and Related Molecules
Effects of substituents on the lengths of the central CâC single bond in the butterfly-shaped anthracene photodimers (1)â(7) and lepidopterenes (8) are studied. X-Ray analysis of the photodimer (10) of 9,10-difluoroanthracene gave a C(9)âC(10âČ) bond length of 1.631 (3)Ă
. An attempt to re-determine molecular structure of the photoisomer (5) of [2.2](9,10) anthracenophane (12) by neutron diffraction analysis is also reported [C(9)âC(10âČ): obs. 1.64(1), calc. 1.63(1)Ă
]. The D_2 structure that had been proposed for the minimum-energy conformation of (5) is questioned and the D_(2h) symmetric conformation is suggested on the basis of the diffraction results and MNDO calculations. The experimentally determined distances of the long central CâC bonds in these butterfly compounds including dianthronyl (9) are well reproduced by MNDO calculations with a standard deviation of 0.013 Ă
. Small but significant further elongation of the central CâC bond by up to 0.07 Ă
resulting from annulation of cyclobutane or cyclopentane ring in anthracene photodimers and from remote chlorine substitution in lepidopterene are interpreted in terms of the increased ÏâÏ^* orbital interaction
An Unaltered Orthosteric Site and a Network of Long-Range Allosteric Interactions for PNU-120596 in α7 Nicotinic Acetylcholine Receptors
Nicotinic acetylcholine receptors (nAChRs) are vital to neuronal signaling, are implicated in important processes such as learning and memory, and are therapeutic targets for neural diseases. The α7 nAChR has been implicated in Alzheimer's disease and schizophrenia, and allosteric modulators have become one focus of drug development efforts. We investigate the mode of action of the α7-selective positive allosteric modulator, PNU-120596, and show that the higher potency of acetylcholine in the presence of PNU-120596 is not due to an altered agonist binding site. In addition, we propose several residues in the gating interface and transmembrane region that are functionally important to transduction of allosteric properties, and link PNU-120596, the acetylcholine binding region, and the receptor gate. These results suggest global protein stabilization from a communication network through several key residues that alter the gating equilibrium of the receptor while leaving the agonist binding properties unperturbed
High resolution radio observations of the colliding-wind binary WR140
Milli-arcsecond resolution Very Long Baseline Array (VLBA) observations of
the archetype WR+O star colliding-wind binary (CWB) system WR140 are presented
for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in
the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that
rotates as the orbit progresses. We interpret this rotation as due to the O
star moving from SE to approximately E of the WR star, which leads to solutions
for the orbit inclination of 122+/-5 deg, the longitude of the ascending node
of 353+/-3 deg, and an orbit semi-major axis of 9.0+/-0.5 mas. The distance to
WR140 is determined to be 1.85+/-0.16 kpc, which requires the O star to be a
supergiant. The inclination implies the mass of the WR and O star to be 20+/-4
and 54+/-10 solar masses respectively. We determine a wind-momentum ratio of
0.22, with an expected half-opening angle for the WCR of 63 deg, consistent
with 65+/-10 deg derived from the VLBA observations. Total flux measurements
from Very Large Array (VLA) observations show the radio emission from WR140 is
very closely the same from one orbit to the next, pointing strongly toward
emission, absorption and cooling mechanism(s) that are controlled largely by
the orbital motion. The synchrotron spectra evolve dramatically through the
orbital phases observed, exhibiting both optically thin and optically thick
emission. We discuss a number of absorption and cooling mechanisms that may
determine the evolution of the synchrotron spectrum with orbital phase.Comment: Accepted by ApJ, to appear in v623, April 20, 2005. 14 pages, 13
figs, requires emulateapj.cls. A version with full resolution figs can be
obtained from http://www.drao.nrc.ca/~smd/preprint/wr140_data.pd
Discovery of extended radio emission in the young cluster Wd1
We present 10 micron, ISO-SWS and Australia Telescope Compact Array
observations of the region in the cluster Wd1 in Ara centred on the B[e] star
Ara C. An ISO-SWS spectrum reveals emission from highly ionised species in the
vicinity of the star, suggesting a secondary source of excitation in the
region. We find strong radio emission at both 3.5cm and 6.3cm, with a total
spatial extent of over 20 arcsec. The emission is found to be concentrated in
two discrete structures, separated by 14''. The westerly source is resolved,
with a spectral index indicative of thermal emission. The easterly source is
clearly extended and nonthermal (synchrotron) in nature. Positionally, the B[e]
star is found to coincide with the more compact radio source, while the
southerly lobe of the extended source is coincident with Ara A, an M2 I star.
Observation of the region at 10micron reveals strong emission with an almost
identical spatial distribution to the radio emission. Ara C is found to have an
extreme radio luminosity in comparison to prior radio observations of hot stars
such as O and B supergiants and Wolf-Rayet stars, given the estimated distance
to the cluster. An origin in a detatched shell of material around the central
star is therefore suggested; however given the spatial extent of the emission,
such a shell must be relatively young (10^3 yrs). The extended non thermal
emission associated with the M star Ara A is unexpected; to the best of our
knowledge this is a unique phenomenon. SAX (2-10keV) observations show no
evidence of X-ray emission, which might be expected if a compact companion were
present.Comment: 5 pages including encapsulated figures, figure 3 separate. Accepted
for MNRAS pink page
A genome-integrated massively parallel reporter assay reveals DNA sequence determinants of cis-regulatory activity in neural cells
Recent large-scale genomics efforts to characterize the cis-regulatory sequences that orchestrate genome-wide expression patterns have produced impressive catalogues of putative regulatory elements. Most of these sequences have not been functionally tested, and our limited understanding of the non-coding genome prevents us from predicting which sequences are bona fide cis-regulatory elements. Recently, massively parallel reporter assays (MPRAs) have been deployed to measure the activity of putative cis-regulatory sequences in several biological contexts, each with specific advantages and distinct limitations. We developed LV-MPRA, a novel lentiviral-based, massively parallel reporter gene assay, to study the function of genome-integrated regulatory elements in any mammalian cell type; thus, making it possible to apply MPRAs in more biologically relevant contexts. We measured the activity of 2,600 sequences in U87 glioblastoma cells and human neural progenitor cells (hNPCs) and explored how regulatory activity is encoded in DNA sequence. We demonstrate that LV-MPRA can be applied to estimate the effects of local DNA sequence and regional chromatin on regulatory activity. Our data reveal that primary DNA sequence features, such as GC content and dinucleotide composition, accurately distinguish sequences with high activity from sequences with low activity in a full chromosomal context, and may also function in combination with different transcription factor binding sites to determine cell type specificity. We conclude that LV-MPRA will be an important tool for identifying cis-regulatory elements and stimulating new understanding about how the non-coding genome encodes information
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