Structural model of a complex between the heterotrimeric G protein, Gsα, and tubulin

AbstractA number of studies have demonstrated interplay between the cytoskeleton and G protein signaling. Many of these studies have determined a specific interaction between tubulin, the building block of microtubules, and G proteins. The α subunits of some heterotrimeric G proteins, including Gsα, have been shown to interact strongly with tubulin. Binding of Gα to tubulin results in increased dynamicity of microtubules due to activation of GTPase of tubulin. Tubulin also activates Gsα via a direct transfer of GTP between these molecules. Structural insight into the interaction between tubulin and Gsα was required, and was determined, in this report, through biochemical and molecular docking techniques. Solid phase peptide arrays suggested that a portion of the amino terminus, α2–β4 (the region between switch II and switch III) and α3–β5 (just distal to the switch III region) domains of Gsα are important for interaction with tubulin. Molecular docking studies revealed the best-fit models based on the biochemical data, showing an interface between the two molecules that includes the adenylyl cyclase/Gβγ interaction regions of Gsα and the exchangeable nucleotide-binding site of tubulin. These structural models explain the ability of tubulin to facilitate GTP exchange on Gα and the ability of Gα to activate tubulin GTPase

A direct search for Dirac magnetic monopoles

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, June 2005.Includes bibliographical references (p. 159-164).Magnetic monopoles are highly ionizing and curve in the direction of the magnetic field. A new dedicated magnetic monopole trigger at CDF, which requires large light pulses in the scintillators of the time-of-flight system, remains highly efficient to monopoles while consuming a tiny fraction of the available trigger bandwidth. A specialized offline reconstruction checks the central drift chamber for large dE/dx tracks which do not curve in the plane perpendicular to the magnetic field. We observed zero monopole candidate events in 35.7 pb⁻¹ of proton-antiproton collisions at ... = 1.96 TeV. This implies a monopole production cross section limit [sigma] 360 GeV.by Michael James Mulhearn.Ph.D

Observing Ultra-High Energy Cosmic Rays with Smartphones

We propose a novel approach for observing cosmic rays at ultra-high energy (> 10 18 eV) by repurposing the existing network of smartphones as a ground detector array. Extensive air showers generated by cosmic rays produce muons and high-energy photons, which can be detected by the CMOS sensors of smartphone cameras. The small size and low efficiency of each sensor is compensated by the large number of active phones. We show that if user adoption targets are met, such a network will have significant observing power at the highest energies

Measurement of spin correlation in ttbar production using a matrix element approach

correlation, assuming that the spin of the top quark is either correlated with the spin of the anti-top quark as predicted by the standard model or is uncorrelated. For the first time we use a matrix-element-based approach to study ttbar spin correlation. We use {ttbar -> W+bW-bbar ->l+nubl-nub} final states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96 TeV, where l denotes an electron or a muon. The data correspond to an integrated luminosity of 5.4 fb-1 and were collected with the dzero detector at the Fermilab Tevatron collider. The result agrees with the standard model prediction. We exclude the hypothesis that the spins of the ttbar are uncorrelated at the 97.7% C.L.Comment: 7 pages, 3 figures, submitted to Phys. Rev. Let

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio