7,990 research outputs found
Biochemical and biophysical studies of MDM2-ligand interactions
MDM2, murine double minute 2, is a RING type-E3 ligase protein and also an oncogene.
MDM2 plays a critical role in determining the steady levels and activity of p53 in cells using
two mechanisms. The N-terminal domain of MDM2 binds to the transactivation domain of
p53 and inhibits its transcriptional activity. The RING domain of MDM2 plays a role in the
ubiquitination (and degradation) of p53. Several proteins are responsible for the
ubiquitination mechanism including the ubiquitin-activating enzyme (E1), ubiquitin-conjugating
enzyme (E2) and ubiquitin ligase (E3). Since the E2-E3 interaction is essential
for ubiquitination, the protein-protein recognition site is a potential drug target.
Two different MDM2 RING constructs were expressed and purified: MDM2RING (residues
386-491) and MDM2RINGâ–³C (residues 386-478). Both constructs were characterised
using dynamic light scattering, size exclusion chromatography, mass spectrometry, NMR
and electron microscopy. E3 ligase activity in vitro was also studied. Taken together these
results showed that the MDM2RING construct formed a concentration-dependent oligomeric
structure. In contrast, the MDM2RINGâ–³C construct formed a dimer at all concentrations.
Both MDM2RING and MDM2RING â–³ C retain E3 ligase activity. However, the
MDM2RINGâ–³C construct is less active. Full length E2 enzyme UbcH5a was also purified.
Various biophysical techniques were used to study its interaction with MDM2 as well as
with potential small molecule inhibitors as in principle, small molecules which disrupt the
interaction between MDM2 and UbcH5a, could prevent/promote ubiquitination of p53.
The dimerisation of MDM2 is important for its E3 activity and the C8-binding site
potentially provides a second druggable site. In this work, peptide 9, which has the same
sequence as the C-terminus of MDMX (an MDM2 homologue) was found to inhibit MDM2
E3 activity. Various biological techniques including NMR, fluorescence anisotropy, and
electrospray mass spectrometry were used to investigate the interaction between two
inhibitory peptides and MDM2. A major part of project involved virtual screening (VS) to
search for small molecules which can affect MDM2-dependent ubiquitination. Three
potential targets were considered: (1) the C8-binding site of MDM2; (2) the UbcH5a-binding
site of MDM2; and (3) the MDM2-binding site of UbcH5a. Several small molecules were
identified using our virtual screening database-mining and docking programs that were
shown to affect MDM2-dependent ubiquitination of p53.
In terms of understanding the complex biochemical mechanism of MDM2 this work
provides two interesting and functionally relevant observations: (i) the MDM2 RINGâ–³C
construct is a dimer as this would not be expected form the existing studies, and has less E3
ligase activity than MDM2RING; (ii) small molecules that bind MDM2 on the E2 binding
site enhanced E3 ligase activity. One model to explain these observations is that binding of
small molecule activators family to the RING induces a change in the conformation of the Cterminal
tail residues which may enhance E2 binding
An Impulsive Three-Species Model with Square Root Functional Response and Mutual Interference of Predator
An impulsive two-prey and one-predator model with square root functional responses, mutual interference, and integrated pest management is constructed. By using techniques of impulsive perturbations, comparison theorem, and Floquet theory, the existence and global asymptotic stability of prey-eradication periodic solution are investigated. We use some methods and sufficient conditions to prove the permanence of the system which involve multiple Lyapunov functions and differential comparison theorem. Numerical simulations are given to portray the complex behaviors of this system. Finally, we analyze the biological meanings of these results and give some suggestions for feasible control strategies
Scaling Analysis of the Tensile Strength of Bamboo Fibers Using Weibull Statistics
This study demonstrates the effect of weak-link scaling on the tensile strength of bamboo fibers. The proposed model considers the random nature of fiber strength, which is reflected by using a two-parameter Weibull distribution function. Tension tests were performed on samples that could be scaled in length. The size effects in fiber length on the strength were analyzed based on Weibull statistics. The results verify the use of Weibull parameters from specimen testing for predicting the strength distributions of fibers of longer gauge lengths
Detection of gamma-ray emission from the Coma cluster with Fermi Large Area Telescope and tentative evidence for an extended spatial structure
Many galaxy clusters have giant halos of non-thermal radio emission,
indicating the presence of relativistic electrons in the clusters. Relativistic
protons may also be accelerated by merger and/or accretion shocks in galaxy
clusters. These cosmic-ray (CR) electrons and/or protons are expected to
produce gamma-rays through inverse-Compton scatterings or inelastic
collisions respectively. Despite of intense efforts in searching for
high-energy gamma-ray emission from galaxy clusters, conclusive evidence is
still missing so far. Here we report the discovery of MeV gamma-ray
emission from the Coma cluster direction with an unbinned likelihood analysis
of the 9 years of {\it Fermi}-LAT Pass 8 data. The gamma-ray emission shows a
spatial morphology roughly coincident with the giant radio halo, with an
apparent excess at the southwest of the cluster. Using the test statistic
analysis, we further find tentative evidence that the gamma-ray emission at the
Coma center is spatially extended. The extended component has an integral
energy flux of in the
energy range of 0.2 - 300 GeV and the spectrum is soft with a photon index of
. Interpreting the gamma-ray emission as arising from CR proton
interaction, we find that the volume-averaged value of the CR to thermal
pressure ratio in the Coma cluster is about . Our results show that
galaxy clusters are likely a new type of GeV gamma-ray sources, and they are
probably also giant reservoirs of CR protons.Comment: 10 pages, 10 figures, Accepted by Physical Review D, more spatial
models for the gamma-ray emission are used, systematic checks on the results
are adde
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