Design and implementation of a biomolecular concentration tracker

As a field, synthetic biology strives to engineer increasingly complex artificial systems in living cells. Active feedback in closed loop systems offers a dynamic and adaptive way to ensure constant relative activity independent of intrinsic and extrinsic noise. In this work, we use synthetic protein scaffolds as a modular and tunable mechanism for concentration tracking through negative feedback. Input to the circuit initiates scaffold production, leading to colocalization of a two-component system and resulting in the production of an inhibitory antiscaffold protein. Using a combination of modeling and experimental work, we show that the biomolecular concentration tracker circuit achieves dynamic protein concentration tracking in Escherichia coli and that steady state outputs can be tuned

High-carrier-density electron dynamics in low-temperature-grown GaAs

Pump-probe differential transmission measurements examine high-carrier-density phenomena in as-grown and annealed GaAs samples grown at temperatures from 210 to 270 °C. We observe trap saturation and Auger recombination, and accurately model the measurements on annealed samples with a simple two level rate equation, allowing us to extract the trapped-electron lifetimes. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70634/2/APPLAB-70-24-3245-1.pd

Endovascular treatment of a Superior Mesenteric Artery Syndrome variant secondary to traumatic pseudoaneurysm

Pseudoaneurysms related to the superior mesenteric artery (SMA) are a recognised complication of trauma to the vessel, and successful treatment with stenting has been previously described. We report the case of a patient who presented with obstruction of the fourth part of the duodenum secondary to a traumatic pseudoaneurysm, a hitherto unreported variant of superior mesenteric artery syndrome. Exclusion of the pseudoaneurysm and relief of the duodenal obstruction were simultaneously achieved by placement of a covered stent

Heavy-quark production and elliptic flow in Au plus Au collisions at root(NN)-N-S=62.4 GeV

We present measurements of electrons and positrons from the semileptonic decays of heavy-flavor hadrons at midrapidity (vertical bar gamma vertical bar \u3c 0.35) in Au + Au collisions at root(NN)-N-S = 62.4 GeV. The data were collected in 2010 by the PHENIX experiment that included the new hadron-blind detector. The invariant yield of electrons from heavy-flavor decays is measured as a function of transverse momentum in the range 1 \u3c p(T)(e) \u3c 5 GeV/c. The invariant yield per binary collision is slightly enhanced above the p + p reference in Au + Au 0%-20%, 20%-40%, and 40%-60% centralities at a comparable level. At this low beam energy this may be a result of the interplay between initial-state Cronin effects, final-state flow, and energy loss in medium. The v(2) of electrons from heavy-flavor decays is nonzero when averaged between 1.3 \u3c p(T)(e) \u3c 2.5 GeV/c for 0%-40% centrality collisions at root(NN)-N-S = 62.4 GeV. For 20%-40% centrality collisions, the v(2) at root(NN)-N-S = 62.4 GeV is smaller than that for heavy-flavor decays at root(NN)-N-S = 200 GeV. The v2 of the electrons from heavy-flavor decay at the lower beam energy is also smaller than v(2) for pions. Both results indicate that the heavy quarks interact with the medium formed in these collisions, but they may not be at the same level of thermalization with the medium as observed at root(NN)-N-S = 200 GeV

The Pfs230 N-terminal fragment, Pfs230D1+: expression and characterization of a potential malaria transmission-blocking vaccine candidate

This work is licensed under a Creative Commons Attribution 4.0 International License.Background Control and elimination of malaria can be accelerated by transmission-blocking interventions such as vaccines. A surface antigen of Plasmodium falciparum gametocytes, Pfs230, is a leading vaccine target antigen, and has recently progressed to experimental clinical trials. To support vaccine product development, an N-terminal Pfs230 antigen was designed to increase yield, as well as to improve antigen quality, integrity, and homogeneity. Methods A scalable baculovirus expression system was used to express the Pfs230D1+ construct (aa 552–731), which was subsequently purified and analysed. Pfs230D1+ was designed to avoid glycosylation and protease digestion, thereby potentially increasing homogeneity and stability. The resulting Pfs230D1+ protein was compared to a previous iteration of the Pfs230 N-terminal domain, Pfs230C1 (aa 443–731), through physiochemical characterization and in vivo analysis. The induction of functional antibody responses was confirmed via the standard membrane feeding assay (SMFA). Results Pfs230D1+ was produced and purified to an overall yield of 23 mg/L culture supernatant, a twofold yield increase over Pfs230C1. The Pfs230D1+ protein migrated as a single band via SDS-PAGE and was detected by anti-Pfs230C1 monoclonal antibodies. Evaluation by SDS-PAGE, chromatography (size-exclusion and reversed phase) and capillary isoelectric focusing demonstrated the molecule had improved homogeneity in terms of size, conformation, and charge. Intact mass spectrometry confirmed its molecular weight and that it was free of glycosylation, a key difference to the prior Pfs230C1 protein. The correct formation of the two intramolecular disulfide bonds was initially inferred by binding of a conformation specific monoclonal antibody and directly confirmed by LC/MS and peptide mapping. When injected into mice the Pfs230D1+ protein elicited antibodies that demonstrated transmission-reducing activity, via SMFA, comparable to Pfs230C1. Conclusion By elimination of an O-glycosylation site, a potential N-glycosylation site, and two proteolytic cleavage sites, an improved N-terminal Pfs230 fragment was produced, termed D1+, which is non-glycosylated, homogeneous, and biologically active. An intact protein at higher yield than that previously observed for the Pfs230C1 fragment was achieved. The results indicate that Pfs230D1+ protein produced in the baculovirus expression system is an attractive antigen for transmission-blocking vaccine development

Measurement of gamma(1S+2S+3S) production in p plus p and Au plus Au collisions at root sNN=200 GeV

Measurements of bottomonium production in heavy-ion and p + p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three states, (1S + 2S + 3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au + Au and p + p collisions at root sNN = 200 GeV. The (1S + 2S + 3S) -\u3e e(+)e(-) differential cross section at midrapidity was found to be B(ee)d sigma/dy = 108 +/- 38 (stat) +/- 15 (syst) +/- 11 (luminosity) pb in p + p collisions. The nuclear modification factor in the 30% most central Au + Au collisions indicates a suppression of the total. state yield relative to the extrapolation from p + p collision data. The suppression is consistent with measurements made by STAR at RHIC and at higher energies by the CMS experiment at the Large Hadron Collider

Centrality dependence of low-momentum direct-photon production in Au plus Au collisions at root s(NN)=200 GeV

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au + Au collisions at root s(NN) = 200 GeV down to pT = 0.4 GeV/c. Photons are detected via photon conversions to e(+)e(-) pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT. We find an excess of direct photons above the N-coll-scaled yield measured in p + p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/c in the pT range 0.6-2.0 GeV/c. While the shape of the pT distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with N-part(alpha), where alpha = 1.38 +/- 0.03(stat) +/- 0.07(syst)