Crystal Structures of the HslVU Peptidase–ATPase Complex Reveal an ATP-Dependent Proteolysis Mechanism

AbstractBackground: The bacterial heat shock locus HslU ATPase and HslV peptidase together form an ATP-dependent HslVU protease. Bacterial HslVU is a homolog of the eukaryotic 26S proteasome. Crystallographic studies of HslVU should provide an understanding of ATP-dependent protein unfolding, translocation, and proteolysis by this and other ATP-dependent proteases.Results: We present a 3.0 Å resolution crystal structure of HslVU with an HslU hexamer bound at one end of an HslV dodecamer. The structure shows that the central pores of the ATPase and peptidase are next to each other and aligned. The central pore of HslU consists of a GYVG motif, which is conserved among protease-associated ATPases. The binding of one HslU hexamer to one end of an HslV dodecamer in the 3.0 Å resolution structure opens both HslV central pores and induces asymmetric changes in HslV.Conclusions: Analysis of nucleotide binding induced conformational changes in the current and previous HslU structures suggests a protein unfolding–coupled translocation mechanism. In this mechanism, unfolded polypeptides are threaded through the aligned pores of the ATPase and peptidase and translocated into the peptidase central chamber

Ground State H-Atom in Born-Infeld Theory

Within the context of Born-Infeld (BI) nonlinear electrodynamics (NED) we revisit the non-relativistic, spinless H-atom. The pair potential computed from the Born-Infeld equations is approximated by the Morse type potential with remarkable fit over the critical region where the convergence of both the short and long distance expansions slows down dramatically. The Morse potential is employed to determine both the ground state energy of the electron and the BI parameter.Comment: 4 pages, 1 figure, final version to appear in Foundation of Physic

Modulational instability of ion-acoustic wave packets in quantum pair-ion plasmas

Amplitude modulation of quantum ion-acoustic waves (QIAWs) in a quantum electron-pair-ion plasma is studied. It is shown that the quantum coupling parameter $H$ (being the ratio of the plasmonic energy density to the Fermi energy) is ultimate responsible for the modulational stability of QIAW packets, without which the wave becomes modulational unstable. New regimes for the modulational stability (MS) and instability (MI) are obtained in terms of $H$ and the positive to negative ion density ratio $\beta$. The growth rate of MI is obtained, the maximum value of which increases with $\beta$ and decreases with $H$. The results could be important for understanding the origin of modulated QIAW packets in the environments of dense astrophysical objects, laboratory negative ion plasmas as well as for the next generation laser solid density plasma experiments.Comment: 4 pages, 2 figures (to appear in Astrophysics and Space Science

Choline, an essential nutrient for humans

Choline is required to make essential membrane phospholipids. It is a precursor for the biosynthesis of the neurotransmitter acetylcholine and also is an important source of labile methyl groups. Mammals fed a choline-deficient diet develop liver dysfunction; however, choline is not considered an essential nutrient in humans. Healthy male volunteers were hospitalized and fed a semisynthetic diet devoid of choline supplemented with 500 mg/day choline for 1 wk. Subjects were randomly divided into two groups, one that continued to receive choline (control), and the other that received no choline (deficient) for three additional wk. During the 5th wk of the study all subjects received choline. The semisynthetic diet contained adequate, but no excess, methionine. In the choline-deficient group, plasma choline and phosphatidylcholine concentrations decreased an average of 30% during the 3-wk period when a choline-deficient diet was ingested; plasma and erthrocyte phosphatidylcholine decreased 15%; no such changes occurred in the control group. In the choline-deficient group, serum alanine aminotransferase activity increased steadily from a mean of 0.42 μkat/liter to a mean of 0.62 μkat/liter during the 3-wk period when a choline-deficient diet was ingested; no such change occurred in the control group. Other tests of liver and renal function were unchanged in both groups during the study. Serum cholesterol decreased an average of 15% in the deficient group and did not change in the control group. Healthy humans consuming a choline-deficient diet for 3 wk had depleted stores of choline in tissues and developed signs of incipient liver dysfunction. Our observations support the conclusion and choline is an essential nutrient for humans when excess methionine and folate are not available in the diet

Regional Adoption of Business-to-Business Electronic Commerce in China: Role of E-Readiness

Adoption of B2B e-commerce is a powerful driver of economic success in developed and developing countries. However, adoption rates in developing countries lag far behind. This paper draws on the Perceived eReadiness Model and research on the influence of inter-organizational relationships and economic-cultural contexts to explain the importance of three factors—inter-organizational power dependence, cooperativeness, and regional economic-cultural differences—for achieving higher levels of Internet-based Electronic Data Interchange (EDI) in the developing country of China. We employ survey data to empirically test both the individual and joint influence of these factors. The findings suggest that beyond intra-organizational and external factors, managers and policy makers wanting to promote Internet-based EDI adoption in developing countries must also account for the inter-organizational relationships of firms and the economic and cultural circumstances of the regions in which they operate

Global Search for New Physics with 2.0/fb at CDF

Data collected in Run II of the Fermilab Tevatron are searched for indications of new electroweak-scale physics. Rather than focusing on particular new physics scenarios, CDF data are analyzed for discrepancies with the standard model prediction. A model-independent approach (Vista) considers gross features of the data, and is sensitive to new large cross-section physics. Further sensitivity to new physics is provided by two additional algorithms: a Bump Hunter searches invariant mass distributions for "bumps" that could indicate resonant production of new particles; and the Sleuth procedure scans for data excesses at large summed transverse momentum. This combined global search for new physics in 2.0/fb of ppbar collisions at sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D Rapid Communication

Observation of Orbitally Excited B_s Mesons

We report the first observation of two narrow resonances consistent with states of orbitally excited (L=1) B_s mesons using 1 fb^{-1} of ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. We use two-body decays into K^- and B^+ mesons reconstructed as B^+ \to J/\psi K^+, J/\psi \to \mu^+ \mu^- or B^+ \to \bar{D}^0 \pi^+, \bar{D}^0 \to K^+ \pi^-. We deduce the masses of the two states to be m(B_{s1}) = 5829.4 +- 0.7 MeV/c^2 and m(B_{s2}^*) = 5839.7 +- 0.7 MeV/c^2.Comment: Version accepted and published by Phys. Rev. Let

Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya

Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization

Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set

We report a measurement of the bottom-strange meson mixing phase \beta_s using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays in which the quark-flavor content of the bottom-strange meson is identified at production. This measurement uses the full data set of proton-antiproton collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity. We report confidence regions in the two-dimensional space of \beta_s and the B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2, -1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in agreement with the standard model expectation. Assuming the standard model value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +- 0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +- 0.009 (syst) ps, which are consistent and competitive with determinations by other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012