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21.
TORSTEN FEDERAU ULRICH SCHUBERT JOSEF FLOßDORF PETER HENKLEIN DIETMAR SCHOMBURG VICTOR WRAY 《Chemical biology & drug design》1996,47(4):297-310
The HIV-1-specific Vpu protein is an 81 amino acid class I integral membrane phosphoprotein that induces degradation of the virus receptor CD4 in the endoplasmic reticulum and enhances the release of virus particles from infected cells. Vpu is of amphipathic nature and consists of a hydrophobic N-terminal membrane anchor proximal to a polar C-terminal cytoplasmic domain. In our recent work, focussed on the structural analysis of the cytoplasmic tail, we established an α-helix-flexible-α-helix-turn model. Now we present the experimental solution structure of the Vpu cytoplasmic domain which has been elucidated in aqueous 50% trifluoroethanol solution by 2D 1H NMR spectroscopy, and restrained molecular dynamics and energy minimization calculations. Under these conditions the peptide, Vpu32-81, is predominantly monomeric and adopts a well defined helix-interconnection-helix-turn conformation, in which the four regions are bounded by residues 37-51, 52-56, 57-72 and 73-78. The presence of the cis isomer of Pro-75 manifests itself as a doubling of cross peaks of neighbouring residues in the 2D spectra. A related variant peptide, Vpum32-81, in which the Vpu-phosphoacceptor sites Ser52 and Ser56 were exchanged for Asn, adopts a very similar structure and, taken together, provides evidence that the second helix and the turn form a comparatively rigid region. Both helices are amphipathic in character, but show different charge distributions. In general the cytoplasmic region is N-terminally positively charged, passes through a region of alternating charges in helix 1 and then becomes negatively charged. The flexibility of the interconnection permits orientational freedom of the two helices. The motif found here is the first experimentally refined solution structure of the cytoplasmic domain of Vpu, and it is conceivable that these α-helices are important for a previously defined physical interaction with an α-helical Vpu-responsive element located within the cytoplasmic tail of CD4. © Munksgaard 1996. 相似文献
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Cyclic tetrapeptides exclusively composed of L- and D-Pro have been studied by theoretical means (conformational searches and molecular mechanics calculations using the CHARMM program) supported by 1H-NMR spectroscopy, X-ray analysis and chiroptical measurements. We explored the entire conformational space of the diastereomers cyclo(LLLL-Pro4) (I), cyc1O(LDLD-Pro4) (II) and CYClo(LLDD-Pro4) (III) including the low-energy conformations and the related interconversion paths. The conformational interconversions were found to be restricted to cis/trans isomerisations of the amide bonds. Owing to the polycyclic nature of cyclo(Pro4) most of the cis/trans transitions are hindered by energy barriers higher than 30 kcal/mol (up to 150–200 kcal/mol). A few transitions are characterized by computed energy barriers comparable to those found in linear -Xxx-Pro- sequences (~ 18 kcal/mol), and are therefore experimentally significant. Experimental evidence has been obtained in the case Of CyClo(LDLD-Pro4), where two enantiomers are interconverted by a series of 4 cis/trans isomerisations ctct→cttt→tttt→tctt→tctc. The Eyring activation parameters of this reaction were determined in H2O and in DMF by chiroptical measurements (ΔH#= 44 and 28 kcal/mol; ΔS#=59 and 22 cal K ?1 mol?1, respectively), and correlated with the calculated barriers. In I and III comparable series of four cis/trans isomerisations relate two main conformations with the peptide bond sequences ctct and tctc. In compound I pseudorotational images are interconverted via ctct→ccct→cctt→cctc→tctc. The pathway ctct→ccct→cctt→cctc→tctc. that relates diastereomeric main conformations of III involves exclusively low-energy intermediates; however, the transitions leading to the all-cis conformation are energetically unfavourable, and the conformational space is divided in three insulated domains. 相似文献
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Classes of tissue hypoxia 总被引:1,自引:0,他引:1
O. SlGGAARD-ANDERSEN A. ULRICH I. H. GTHGEN 《Acta anaesthesiologica Scandinavica》1995,39(S107):137-142
We identify eight causes of tissue hypoxia, falling into three classes, A, B, and C, depending upon the effect on the critical mixed venous p O2 and the optimal oxygen consumption rate. The critical mixed venous p O2 is the value above which the oxygen consumption rate is optimal and independent of the mixed venous p O2 and below which the oxygen consumption rate decreases towards zero. Class A hypoxia: primary decrease in mixed venous p O2 . Causes: 1) ischaemic hypoxia (decrease in cardiac output), 2) low-extractivity hypoxia (decrease in oxygen extraction tension, p 8 ). Class B hypoxia: primary increase in critical mixed venous p O2 . Causes: 1) shunt hypoxia (increased a-v shunting), 2) dysperfusion hypoxia (increased diffusion length from erythrocytes to mitochondria and/or decreased total capillary endothelial diffusion area, e. g., tissue oedema, microembolism), 3) histotoxic hypoxia (inhibition of the cytochrome chain). Class C hypoxia: primary increase in optimal oxygen consumption rate. Causes: 1) uncoupling hypoxia (uncoupling of the ATP formation associated with O2 reduction), 2) hypermetabolic hypoxia (increased energy metabolism, e. g., due to hyperthermia). 相似文献
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Chronic Inhalation of Short Asbestos Fibers 总被引:1,自引:0,他引:1
PLATEK S. FRANK; GROTH DAVID H.; ULRICH CHARLES E.; STETTLER LLOYD E.; FTNNELL MYRA S.; STOLL MARGRIT 《Toxicological sciences》1985,5(2):327-340
Chronic Inhalation of Short Asbestos Fibers. PLATEK, S. F.,GROTH, D. H., ULRICH, C. E., STETTLER, L. E., FINNELL, M. S.,AND STOLL, M. (1985). Fundam. Appl. Toxicol. 5, 327340.An animal inhalation study was initiated to study the chronicbiological effects of inhalation of short chrysotile asbestosfibers. Rats and monkeys were exposed for 18 months, 7 hr/day,5 days/week to a specially prepared, chrysotile asbestos aerosol.Based upon daily chamber measurements, the mean concentrationof fibers in the chamber air was 1.0 mg/m3. By phase contrastmicroscopy, the number of fibers > 5 µm in length wasdetermined to be 0.79 fiber per cubic centimeter. Rats wereautopsied for pathological and histochemical examination at1, 3, 6, 12, 18, and 24 months after initiating exposures. Nosignificnt differences in the histochemical data were seen betweenthe exposed and control groups. Gross and histopathologic examinationof exposed and control groups of rats indicated no compound-relatedlesions, including fibrosis. Open lung biopsies were performedon the chrysotile-exposed and the control monkeys 28 monthsafter initiating exposures. Histopathologic evaluation of thelung biopsy tissue showed the presence of asbestos bodies adjacentto the terminal bronchioles of the asbestos-exposed monkeys.There was no observed fibrosis in pulmonary tissue. All monkeysare being maintained for an indefinite period and observed forsigns of latent pulmonary disease. 相似文献
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