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171.
Angstrom J; Teneberg S; Milh MA; Larsson T; Leonardsson I; Olsson BM; Halvarsson MO; Danielsson D; N aslund I; Ljungh A; Wadstrom T; Karlsson KA 《Glycobiology》1998,8(4):297-309
The possible role of glycosphingolipids as adhesion receptors for the human
gastric pathogen Helicobacter pylori was examined by use of radiolabeled
bacteria, or protein extracts from the bacterial cell surface, in the
thin-layer chromatogram binding assay. Of several binding specificities
found, the binding to lactosylceramide is described in detail here, the
others being reported elsewhere. By autoradiography a preferential binding
to lactosylceramide having sphingosine/phytosphingosine and 2-D hydroxy
fatty acids was detected, whereas lactosylceramide having sphingosine and
nonhydroxy fatty acids was consistently nonbinding. A selective binding of
H. pylori to lactosylceramide with phytosphingosine and 2-D hydroxy fatty
acid was obtained when the different lactosylceramide species were
incorporated into liposomes, but only in the presence of cholesterol,
suggesting that this selectivity may be present also in vivo . Importantly,
lactosylceramide with sphingosine and hydroxy fatty acids does not bind in
this assay. Furthermore, a lactosylceramide-based binding pattern obtained
for different trisaccharide glycosphingolipids is consistent with the
assumption that this selectivity is due to binding of a conformation of
lactosylceramide in which the oxygen of the 2-D fatty acid hydroxyl group
forms a hydrogen bond with the Glc hydroxy methyl group, yielding an
epitope presentation different from other possible conformers. An
alternative conformation that may come into consideration corresponds to
the crystal structure found for cerebroside, in which the fatty acid
hydroxyl group is free to interact directly with the adhesin. By isolating
glycosphingolipids from epithelial cells of human stomach from seven
individuals, a binding of H.pylori to the diglycosylceramide region of the
non-acid fraction could be demonstrated in one of these cases. Mass
spectrometry showed that the binding-active sample contained
diglycosylceramides with phytosphingosine and 2-D hydroxy fatty acids with
16-24 carbon atoms in agreement with the results related above.
相似文献
172.
Moreno E; Lanne B; Vazquez AM; Kawashima I; Tai T; Fernandez LE; Karlsson KA; Angstrom J; Perez R 《Glycobiology》1998,8(7):695-705
P3 is a mouse monoclonal antibody (mAb) that binds to several NeuGc-
containing gangliosides. It also reacts with antigens expressed in human
breast tumors (Vazquez et al. (1995) Hybridoma , 14, 551-556). In this
work, the binding specificity of P3 has been characterized in more detail
using a panel of glycolipids that included several disialylated
gangliosides and several chemical derivatives of NeuGc-GM3. The carboxyl
group and the nitrogen function of sialic acid were found to play important
roles in the antibody binding, whereas the glycerol tail appears to be
nonrelevant. Molecular modeling was used to analyze the binding data,
including the finding that P3 selectively recognizes the internal NeuGc in
GD3. For this purpose, conformational studies of GD3 were performed using
molecular dynamics. It was concluded that sialic acid binds the P3 antibody
through its upper face (the one on which the carboxyl group is exposed) and
the C4-C5 side of the sugar ring, whereas none or very little contact
between the galactose residue and the protein is evident. Conformational
analysis of GD3 revealed that, despite the large flexibility of the
NeuGcalpha8NeuGc linkage, the P3 binding epitope on the external sialic
acid is not well exposed for any of the possible conformations this linkage
can adopt, whereas the internal sialic acid presents the epitope in a
proper way for several of these conformations. As a final result, a
coherent picture of the epitope that fits the wide binding data was
obtained.
相似文献
173.
A recombination based method to rapidly assess specificity of two-hybrid clones in yeast. 总被引:1,自引:0,他引:1 下载免费PDF全文
The yeast two-hybrid system is frequently used to identify protein-protein interactions. Confirming the specificity of candidate clones requires separation and isolation of yeast plasmids, propagation in bacteria and testing combinations of DNA-binding and activation domain hybrids in yeast. In order to simplify this procedure, we developed a rapid method based on PCR amplification of library insert DNAs and in vivo cloning into the activation domain hybrid vector. Reporter gene activity is assayed in parallel for combinations with different DNA-binding domain hybrids. Further characterization of inserts does not require plasmid isolation and intermediate hosts. 相似文献
174.
Restriction mapping is used to estimate nucleotide sequence polymorphism
when the regions to be studied are too long or too numerous to be
sequenced. Restriction mapping is less costly than DNA sequencing, but it
does not allow direct measurement of underlying nucleotide polymorphism. It
is therefore useful to be able to estimate underlying nucleotide
polymorphism from observations of polymorphism in restriction maps, as this
offers some of the resolution afforded by DNA sequencing at a reduced cost.
Previous estimators of underlying nucleotide polymorphism have assumed that
each restriction-enzyme- binding site contains, at most, a single
polymorphic nucleotide position (the low-polymorphism-frequency
assumption), and this assumption has placed an upper limit on the level of
polymorphism that can be resolved by these estimators. The present study
documents an estimator which allows relaxation of this assumption. The new
estimator more accurately estimates underlying nucleotide polymorphism when
the polymorphism level is high enough to falsify the low-polymorphism-
frequency assumption. The new estimator therefore yields good results for
data sets that are too divergent for analysis by present methods.
相似文献
175.
176.
The biogeochemistry of basic cations in two forest catchments with contrasting lithology in the Czech Republic 总被引:2,自引:0,他引:2
PAVEL KRÁM JAKUB HRUŠKA BRIAN S. WENNER CHARLES T. DISCOLL CHRIS E. JOHNSON 《Biogeochemistry》1997,37(2):173-202
The biogeochemistry of Ca, Mg, K, and Nawere investigated in two forested catchments in theCzech Republic, one underlain by leucogranite, theother by serpentinite. High weathering rates at theserpentinite site at Pluhv Bor resultedin Mg2+ as the dominant cation on the soilexchange complex and in drainage water. Other basiccations (Ca2+, K+, Na+) showedrelatively low concentrations and outflow instreamwater. The catchment exhibited high basesaturation in mineral soils (>70%), and nearneutral soil and stream pH, despite elevated inputsof acidic deposition. Slow growth of Norway spruceat Pluhv Bor may be caused by K deficiency, Mgoversupply and/or Ni toxicity. In contrast, thegranitic site at Lysina showed low concentrations ofbasic cations on the soil exchange complex and instreamwater. Soil and drainage water at Lysina werehighly impacted by acidic deposition. Soil pH wasextremely acidic (<4.5) throughout the soilprofile, and the base saturation of the mineral soilwas very low (<5%). Supplies of basic cationsfrom atmospheric deposition and soil processes wereless than inputs of SO2-
4 on anequivalence basis, resulting in low pH and highconcentrations of total Al in drainage water. Needle yellowing in Norway spruce was possibly theresult of Mg deficiency at Lysina. Because of theirextremely different lithologies, these catchmentsserve as valuable end-members of ecosystemsensitivity to elevated levels of acidicdeposition. 相似文献
177.
ZDENEK IKA 《The Journal of eukaryotic microbiology》1972,19(2):275-280
SYNOPSIS. In an electron microscope study of the neogregarine Farinocystis tribolii Weiser 1953 in the fat body of the larvae of the flour beetle Tribolium castaneum , empty oocysts and adjacent sporozoites of the gregarine were found. The empty oocysts contained host cell cytoplasm, a residuum only slightly larger than that in mature oocysts, and some remnants of the oocyst membrane pressed tightly against the inner surface of the wall. Apparently normal sporozoites were found near the empty oocysts and no damaged ones were seen. It is assumed that the sporozoites go on developing in the host, i.e., that autoinfection takes place. 相似文献
178.
ANETT HARSÁNYI MARGARETA RYBERG MATS X. ANDERSSON KÁROLY BÓKA LAJOS LÁSZLÓ GERGELY BOTOND BÉLA BÖDDI RICHARD GÁBORJÁNYI 《Molecular Plant Pathology》2006,7(6):533-541
To understand the phenomenon by which infection of seed-transmitted Barley stripe mosaic virus (BSMV) alters membrane structures and inhibits protochlorophyllide biosynthesis of dark-grown barley ( Hordeum vulgare L.) plants, we analysed the presence of NADPH:protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) and the galactolipid content and fatty acid composition. The amount of POR in etioplasts of infected leaves, compared with non-infected leaves, was reduced, as measured by immunoelectron microscopy and Western blot. These results are in agreement with the previously described reduction of the ratio of the photoactive 650 nm to non-photoactive 630 nm absorbing protochlorophyllide forms ( Harsányi et al. , 2002 . Physiol. Plant 114 , 149–155). The galactolipid content was lower in infected leaves. Monogalactosyl-diacylglycerol (MGDG) content was reduced to 40% and digalactosyl-diacylglycerol to 55% of control plants on a fresh weight basis. In infected plants, the proportion of linolenic acid decreased in both galactolipids. The lower amount of highly unsaturated fatty acids and the reduced abundance of MGDG correlated well with the previously detected reduction in the membrane ratio of prolamellar body (PLB) to prothylakoid ( Harsányi et al. , 2002 . Physiol. Plant 114 , 149–155). The reduced amount of POR and the above described alterations in the lipid composition resulted in a disturbed structure of PLBs. As a consequence, pigment synthesis and the greening process were inhibited in infected cells, in turn explaining the appearance of chlorotic stripes of BSMV-infected barley leaves. Our results show that BSMV infection can be detected at a very early stage of leaf development. 相似文献
179.
Latrunculin B has different effects on pollen germination and tube growth 总被引:27,自引:0,他引:27 下载免费PDF全文
The actin cytoskeleton is absolutely required for pollen germination and tube growth, but little is known about the regulation of actin polymer concentrations or dynamics in pollen. Here, we report that latrunculin B (LATB), a potent inhibitor of actin polymerization, had effects on pollen that were distinct from those of cytochalasin D. The equilibrium dissociation constant measured for LATB binding to maize pollen actin was determined to be 74 nM. This high affinity for pollen actin suggested that treatment of pollen with LATB would have marked effects on actin function. Indeed, LATB inhibited maize pollen germination half-maximally at 50 nM, yet it blocked pollen tube growth at one-tenth of that concentration. Low concentrations of LATB also caused partial disruption of the actin cytoskeleton in germinated maize pollen, as visualized by light microscopy and fluorescent-phalloidin staining. The amounts of filamentous actin (F-actin) in pollen were quantified by measuring phalloidin binding sites, a sensitive assay that had not been used previously for plant cells. The amount of F-actin in maize pollen increased slightly upon germination, whereas the total actin protein level did not change. LATB treatment caused a dose-dependent depolymerization of F-actin in populations of maize pollen grains and tubes. Moreover, the same concentrations of LATB caused similar depolymerization in pollen grains before germination and in pollen tubes. These data indicate that the increased sensitivity of pollen tube growth to LATB was not due to general destabilization of the actin cytoskeleton or to decreases in F-actin amounts after germination. We postulate that germination is less sensitive to LATB than tube extension because the presence of a small population of LATB-sensitive actin filaments is critical for maintenance of tip growth but not for germination of pollen, or because germination is less sensitive to partial depolymerization of the actin cytoskeleton. 相似文献
180.