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排序方式: 共有1601条查询结果,搜索用时 15 毫秒
81.
B. Yassine-Diab P. Carmichael Fatima-Ezzahra L'Faqihi Giovanna Lombardi Sarah Deacock Claude de Préval Hélène Coppin R. I. Lechler 《Immunogenetics》1999,49(6):532-540
A comprehensive analysis was carried out of the tri-molecular complex of peptide, major histocompatibility class II molecule,
and T-cell receptor (TcR) involved in the recognition of the promiscuous HA (306–318) peptide, restricted by one of two closely
related HLA-DR alleles, HLA-DRB1*0101 and HLA-DRB1*0103. These two DR molecules differ by only three amino acids at positions 67, 70, and 71, in the third variable region of the
DRB1 chain. None of the HA (306–318)-specific T-cell clones restricted by these two DR molecules tolerated amino acid substitution
at the peptide-binding position 71, despite the fact that the substitution did not interfere with peptide binding. The majority
of the DRB1*0103-restricted clones tolerated substitution of the amino acid at the TcR-contacting position 70, while the DRB1*0101-restricted
T cells did not. Biased usage of TRVA and TRVB segments was observed for the DRB1*0103-restricted clones; in contrast, apparently
random usage was seen in the DRB1*0101-restricted T cells. Finally, limiting dilution analysis revealed a lower frequency
of T cells reactive with the HA peptide in a DRB1*0103 compared with a DRB1*0101 individual. Taken together these data suggest
that biased TcR gene usage may reflect a relatively low precursor frequency of T cells, and the need for clonal expansion of a limited set
of high avidity T cells.
Received: 7 August 1998 / Revised: 19 November 1998 相似文献
82.
Pierleoni R Buffalini M Vallorani L Guidi C Zeppa S Sacconi C Pucci P Amoresano A Casbarra A Stocchi V 《Phytochemistry》2004,65(7):813-820
The formation of the fruit body represents the final phase of the ectomycorrhizal fungus T. borchii life cycle. Very little is known concerning the molecular and biochemical processes involved in the fructification phase. 2-DE maps of unripe and ripe ascocarps revealed different protein expression levels and the comparison of the electropherograms led to the identification of specific proteins for each developmental phase. Associating micropreparative 2-DE to microchemical approaches, such as N-terminal sequencing and 2-D gel-electrophoresis mass-spectrometry, proteins playing pivotal roles in truffle physiology were identified. 相似文献
83.
Targeted modification of homogalacturonan by transgenic expression of a fungal polygalacturonase alters plant growth
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Capodicasa C Vairo D Zabotina O McCartney L Caprari C Mattei B Manfredini C Aracri B Benen J Knox JP De Lorenzo G Cervone F 《Plant physiology》2004,135(3):1294-1304
Pectins are a highly complex family of cell wall polysaccharides comprised of homogalacturonan (HGA), rhamnogalacturonan I and rhamnogalacturonan II. We have specifically modified HGA in both tobacco (Nicotiana tabacum) and Arabidopsis by expressing the endopolygalacturonase II of Aspergillus niger (AnPGII). Cell walls of transgenic tobacco plants showed a 25% reduction in GalUA content as compared with the wild type and a reduced content of deesterified HGA as detected by antibody labeling. Neutral sugars remained unchanged apart from a slight increase of Rha, Ara, and Gal. Both transgenic tobacco and Arabidopsis were dwarfed, indicating that unesterified HGA is a critical factor for plant cell growth. The dwarf phenotypes were associated with AnPGII activity as demonstrated by the observation that the mutant phenotype of tobacco was completely reverted by crossing the dwarfed plants with plants expressing PGIP2, a strong inhibitor of AnPGII. The mutant phenotype in Arabidopsis did not appear when transformation was performed with a gene encoding AnPGII inactivated by site directed mutagenesis. 相似文献
84.
Verde C Howes BD De Rosa MC Raiola L Smulevich G Williams R Giardina B Parisi E Di Prisco G 《Protein science : a publication of the Protein Society》2004,13(10):2766-2781
The suborder Notothenioidei dominates the Antarctic ichthyofauna. The non-Antarctic monotypic family Pseudaphritidae is one of the most primitive families. The characterization of the oxygen-transport system of euryhaline Pseudaphritis urvillii is herewith reported. Similar to most Antarctic notothenioids, this temperate species has a single major hemoglobin (Hb 1, over 95% of the total). Hb 1 has strong Bohr and Root effects. It shows two very uncommon features in oxygen binding: At high pH values, the oxygen affinity is exceptionally high compared to other notothenioids, and subunit cooperativity is modulated by pH in an unusual way, namely the curve of the Hill coefficient is bell-shaped, with values approaching 1 at both extremes of pH. Molecular modeling, electronic absorption and resonance Raman spectra have been used to characterize the heme environment of Hb 1 in an attempt to explain these features, particularly in view of some potentially important nonconservative replacements found in the primary structure. Compared to human HbA, no major changes were found in the structure of the proximal cavity of the alpha-chain of Hb 1, although an altered distal histidyl and heme position was identified in the models of the beta-chain, possibly facilitated by a more open heme pocket due to reduced steric constraints on the vinyl substituent groups. This conformation may lead to the hemichrome form identified by spectroscopy in the Met state, which likely fulfils a potentially important physiological role. 相似文献
85.
Herpes simplex virus glycoprotein K,but not its syncytial allele,inhibits cell-cell fusion mediated by the four fusogenic glycoproteins,gD, gB,gH, and gL
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A Myc epitope was inserted at residue 283 of herpes simplex virus type 1 (HSV-1) glycoprotein K (gK), a position previously shown not to interfere with gK activity. The Myc-tagged gK localized predominantly to the endoplasmic reticulum, both in uninfected and in HSV-infected cells. gK, coexpressed with the four HSV fusogenic glycoproteins, gD, gB, gH, and gL, inhibited cell-cell fusion. The effect was partially dose dependent and was observed both in baby hamster kidney (BHK) and in Vero cells, indicating that the antifusion activity of gK may be cell line independent. The antifusion activity of gK did not require viral proteins other than the four fusogenic glycoproteins. A syncytial (syn) allele of gK (syn-gK) carrying the A40V substitution present in HSV-1(MP) did not block fusion to the extent seen with the wild-type (wt) gK, indicating that the syn mutation ablated, at least in part, the antifusogenic activity of wt gK. We conclude that gK is part of the mechanism whereby HSV negatively regulates its own fusion activity. Its effect accounts for the notion that cells infected with wt HSV do not fuse with adjacent, uninfected cells into multinucleated giant cells or syncytia. gK may also function to preclude fusion between virion envelope and the virion-encasing vesicles during virus transport to the extracellular compartment, thus preventing nucleocapsid de-envelopment in the cytoplasm. 相似文献
86.
87.
88.
Maccaglia A Mallozzi C Minetti M 《Biochemical and biophysical research communications》2003,305(3):541-547
The protective effects of eating fruits and vegetables in the prevention of several degenerative pathologies have been attributed at least in part to the antioxidant and anti-inflammatory properties of polyphenols. In this study, we investigated the effects of two polyphenols, quercetin and resveratrol, on red blood cell Band 3 tyrosine phosphorylation signalling activated by peroxynitrite. Peroxynitrite is a physiological oxidant scavenged largely by the erythrocyte and formed by the reaction between nitrogen monoxide and superoxide anion. Quercetin and its structurally analogous (+)-catechin inhibited the peroxynitrite-dependent upregulation of Band 3 tyrosine phosphorylation. Quercetin was found to downregulate the activity of syk, which is upstream in the Band 3 tyrosine phosphorylation cascade, and partially prevented peroxynitrite-mediated phosphotyrosine phosphatase inhibition. Resveratrol and hydroxytyrosol, unexpectedly, amplified peroxynitrite-dependent upregulation of Band 3 tyrosine phosphorylation through the activation of lyn, a kinase of the src family. The present results clearly indicate that polyphenols may activate cell transduction pathways in different and sometimes opposite ways. 相似文献
89.
Romani R Antognelli C Baldracchini F De Santis A Isani G Giovannini E Rosi G 《Chemico-biological interactions》2003,145(3):321-329
The present study looks at possible changes in the activity of acetylcholinesterase (AChE) in tissues (brain and white muscle) of the Mediterranean bony fish Sparus auratus after a 20 days exposure to sublethal concentrations (0.1 or 0.5 ppm) of copper in the marine water and on control untreated animals. The trials also included measurements of Cu concentration in the tissues to evaluate possible metal accumulation. Moreover, sedimentation analysis as well as V(max) and K(m) determination were carried out in tissue extracts of Cu-exposed or control animals. V(max) and K(m) were also determined with or without addition of Cu(2+) in the assay. No Cu accumulation occurred in brain and muscle after Cu exposure. AChE showed in both tissues a molecular polymorphism with putative globular (G) and asymmetric (A) forms. Cu exposition led to an increased specific activity and improved catalytic efficiency of AChE in brain and muscle, seemingly regarding G forms. The increase in catalytic efficiency also resulted from the in vitro assay with tissue extracts and Cu(2+) addition. The higher AChE activity and catalytic efficiency in both tissues after Cu exposition and without metal accumulation, suggests an increase of free Cu aliquot into the cells, likely due to mechanisms of metal homeostasis. 相似文献
90.
Lutgarde Thijs Jan A Staessen Sonia Beleva Willem H Birkenhäger Christopher J Bulpitt Hilde Celis Astrid E Fletcher Rumjana Kermova Gastone Leonetti Tovio Laks Stefan Mantov Choudomir Nachev Cinzia Sarti Jaakko Tuomilehto Robert H Fagard 《Trials》2001,2(6):1-9