980 research outputs found
Structural basis for inhibition of the epidermal growth factor receptor by cetuximab
SummaryRecent structural studies of epidermal growth factor receptor (EGFR) family extracellular regions have identified an unexpected mechanism for ligand-induced receptor dimerization that has important implications for activation and inhibition of these receptors. Here we describe the 2.8 Ă
resolution X-ray crystal structure of the antigen binding (Fab) fragment from cetuximab (Erbitux), an inhibitory anti-EGFR antibody, in complex with the soluble extracellular region of EGFR (sEGFR). The sEGFR is in the characteristic âautoinhibitedâ or âtetheredâ inactive configuration. Cetuximab interacts exclusively with domain III of sEGFR, partially occluding the ligand binding region on this domain and sterically preventing the receptor from adopting the extended conformation required for dimerization. We suggest that both these effects contribute to potent inhibition of EGFR activation
Structural Evaluation of EGFR Inhibition Mechanisms for Nanobodies/VHH Domains
SummaryThe epidermal growth factor receptor (EGFR) is implicated in human cancers and is the target of several classes of therapeutic agents, including antibody-based drugs. Here, we describe X-ray crystal structures of the extracellular region of EGFR in complex with three inhibitory nanobodies, the variable domains of heavy chain only antibodies (VHH). VHH domains, the smallest natural antigen-binding modules, are readily engineered for diagnostic and therapeutic applications. All three VHH domains prevent ligand-induced EGFR activation, but use two distinct mechanisms. 7D12 sterically blocks ligand binding to EGFR in a manner similar to that of cetuximab. EgA1 and 9G8 bind an epitope near the EGFR domain II/III junction, preventing receptor conformational changes required for high-affinity ligand binding and dimerization. This epitope is accessible to the convex VHH paratope but inaccessible to the flatter paratope of monoclonal antibodies. Appreciating the modes of binding and inhibition of these VHH domains will aid in developing them for tumor imaging and/or cancer therapy
A single codon insertion in PICALM is associated with development of familial subvalvular aortic stenosis in Newfoundland dogs
Familial subvalvular aortic stenosis (SAS) is one of the most common congenital heart defects in dogs and is an inherited defect of Newfoundlands, golden retrievers and human children. Although SAS is known to be inherited, specific genes involved in Newfoundlands with SAS have not been defined. We hypothesized that SAS in Newfoundlands is inherited in an autosomal dominant pattern and caused by a single genetic variant. We studied 93 prospectively recruited Newfoundland dogs, and 180 control dogs of 30 breeds. By providing cardiac screening evaluations for Newfoundlands we conducted a pedigree evaluation, genome-wide association study and RNA sequence analysis to identify a proposed pattern of inheritance and genetic loci associated with the development of SAS. We identified a three-nucleotide exonic insertion in phosphatidylinositol-binding clathrin assembly protein (PICALM) that is associated with the development of SAS in Newfoundlands. Pedigree evaluation best supported an autosomal dominant pattern of inheritance and provided evidence that equivocally affected individuals may pass on SAS in their progeny. Immunohistochemistry demonstrated the presence of PICALM in the canine myocardium and area of the subvalvular ridge. Additionally, small molecule inhibition of clathrin-mediated endocytosis resulted in developmental abnormalities within the outflow tract (OFT) of Xenopus laevis embryos. The ability to test for presence of this PICALM insertion may impact dog-breeding decisions and facilitate reduction of SAS disease prevalence in Newfoundland dogs. Understanding the role of PICALM in OFT development may aid in future molecular and genetic investigations into other congenital heart defects of various species
Vector species-specific association between natural Wolbachia infections and avian malaria in black fly populations
Thanks to the Institute of Biodiversity Animal Health and Comparative Medicine (University of Glasgow) for funding vector traps.Artificial infection of mosquitoes with the endosymbiont bacteria Wolbachia can interfere with malaria parasite development. Therefore, the release of Wolbachia-infected mosquitoes has been proposed as a malaria control strategy. However, Wolbachia effects on vector competence are only partly understood, as indicated by inconsistent effects on malaria infection reported under laboratory conditions. Studies of naturally-occurring Wolbachia infections in wild vector populations could be useful to identify the ecological and evolutionary conditions under which these endosymbionts can block malaria transmission. Here we demonstrate the occurrence of natural Wolbachia infections in three species of black fly (genus Simulium), which is a main vector of the avian malaria parasite Leucocytozoon. Prevalence of Leucocytozoon was high (25%), but the nature and magnitude of its association with Wolbachia differed between black fly species. Wolbachia infection was positively associated with avian malaria infection in S. cryophilum, negatively associated in S. aureum, and unrelated in S. vernum. These differences suggest that Wolbachia interacts with the parasite in a vector host species-specific manner. This provides a useful model system for further study of how Wolbachia influences vector competence. Such knowledge, including the possibility of undesirable positive association, is required to guide endosymbiont based control methods.Publisher PDFPeer reviewe
Probing the Nature of the G1 Clump Stellar Overdensity in the Outskirts of M31
We present deep HST/ACS observations of the G1 clump, a distinct stellar
overdensity lying at ~30 kpc along the south-western major axis of M31 close to
the G1 globular cluster (Ferguson et al. 2002). Our well-populated
colour-magnitude diagram reaches ~7 magnitudes below the red giant branch tip
with 90% completeness, and allows the detection of various morphological
features which can be used to derive detailed constraints on the age and
metallicity of the constituent stellar population. We find that the
colour-magnitude diagram is best described by a population with a large age
range (>= 10 Gyr) and a relatively high mean metallicity [M/H]= -0.4. The
spread in metallicity is constrained to be <=0.5 dex. The star formation rate
in this region has declined over time, with the bulk of the stellar mass having
formed >6 Gyr ago. Nonetheless, a non-negligible mass fraction (approximately
10%) of the population has formed in the last 2 Gyr. We discuss the nature of
the G1 Clump in light of these new stellar population constraints and argue
that the combination of stellar content and physical size make it unlikely that
the structure is the remnant of an accreted dwarf galaxy. Instead, the strong
similarity between the stellar content of the G1 Clump and that of the M31
outer disk suggests the substructure is a fragment of the outer disk, perhaps
torn off from the main body during a past accretion/merger event; this
interpretation is consistent with extant kinematical data. If this
interpretation is correct, our analysis of the stellar content provides further
evidence that the outskirts of large disk galaxies have been in place for a
significant time.Comment: Accepted for publication in AJ. 13 pages, 12 figures. Figure 1, 5, 9,
and 10 at reduced resolution. High resolution version available at
http://www.astro.lu.se/~daniel/g1/g1.p
The Stellar Populations of M31 Halo Substructure
We present the first results from our survey of stellar substructure in the
outskirts of M31 using the Advanced Camera for Surveys (ACS) on board the
Hubble Space Telescope. We discuss the stellar populations associated with five
prominent stellar overdensities discovered during the course of our panoramic
ground-based imaging survey with the Isaac Newton Telescope Wide-Field Camera
(INT WFC); a sixth pointing targets a region of `clean' halo. The
colour-magnitude diagrams (CMDs), which contain between ~10,000--90,000 stars
and reach four magnitudes below the horizontal branch, reveal clear variations
in morphology between most fields, indicating that the age and/or metallicity
mix of stars is not constant at large radius. This directly confirms the
existence of large-scale population inhomogeneities within the halo of M31 and
lends further support to the notion that M31 has formed, at least in part,
through satellite accretions. We find a striking similarity between the
populations of the giant stellar stream and those of another overdensity, the
NE shelf, which lies north-east of the galaxy center. If these overdensities
are associated with the same population, then the difference in their red clump
magnitudes implies the NE shelf lies in front of the stream by several tens of
kpc, in good agreement with recent orbit calculations for the stream
progenitor.Comment: 5 pages, 3 figurs, ApJL accepte
Heard, valued, supported? : Doctors' wellbeing during transitions triggered by COVID-19
Funding Information: The authors would like to thank all study participants who invested significant time and energy into participating in this study in exceptional circumstances. The authors would also like to thank study funders: Chief Scientist Office (Scotland) and Scottish Medical Education Research Consortium (SMERC). Publisher Copyright: © 2021 The Authors. Medical Education published by Association for the Study of Medical Education and John Wiley & Sons Ltd.Peer reviewedPublisher PD
The Stellar Content of Galaxy Halos: A Comparison between LambdaCDM Models and Observations of M31
Recent observations have revealed that high surface-brightness, metal-rich
debris is present over large regions of the Andromeda (M31) stellar halo. We
use a set of numerical models to determine whether extended metal-rich debris
is expected to exist in galaxy halos formed in a hierarchical LambdaCDM
universe. We identify tidal debris in the simulations according to the current
best surface brightness detection limits in M31 and demonstrate that bright
features in the outer halo regions usually originate from single satellites,
with very little contamination from other sources due to the low probability of
tidal streams from two overlapping accretion events. In contrast, high-surface
brightness features in the inner halo often originate from multiple
progenitors. We also compare the age and metallicity distribution of the debris
with the well-mixed stellar halos in which they reside. We find that
high-surface brightness tidal debris is produced almost exclusively by
relatively high mass progenitors (Mstar ~ 10^7- 10^9 Msun) and thus is expected
to be of moderate- to high-metallicity. Similarly, in our models the smooth
inner halo is expected to be metal-rich as this region has been built up mainly
from massive satellites. Our results imply that the stellar populations of
substructure observed around external galaxies with current techniques should
not resemble old and metal-poor dwarf spheroidal satellites, nor the underlying
component of the stellar halo.Comment: 12 pages, 8 figures (accepted to ApJ
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