| 1. |
- Aspholm-Hurtig, Marina, et al.
(författare)
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Functional adaptation of BabA, the H. pylori ABO blood group antigen binding adhesin.
- 2004
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Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 305:5683, s. 519-22
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Tidskriftsartikel (refereegranskat)abstract
- Adherence by Helicobacter pylori increases the risk of gastric disease. Here, we report that more than 95% of strains that bind fucosylated blood group antigen bind A, B, and O antigens (generalists), whereas 60% of adherent South American Amerindian strains bind blood group O antigens best (specialists). This specialization coincides with the unique predominance of blood group O in these Amerindians. Strains differed about 1500-fold in binding affinities, and diversifying selection was evident in babA sequences. We propose that cycles of selection for increased and decreased bacterial adherence contribute to babA diversity and that these cycles have led to gradual replacement of generalist binding by specialist binding in blood group O-dominant human populations.
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| 2. |
- Richardson, Sara, et al.
(författare)
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Enzyme-aided investigation of the substituent distribution in cationic potato amylopectin starch
- 2003
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 75:23, s. 6499-6508
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of substituents along the polymer chain in cationic potato amylopectin starch, modified in solution, granular slurry, or dry state, was investigated. The starch derivatives were successively hydrolyzed by different enzymes, followed by characterization of the hydrolysis products obtained by means of electrospray mass spectrometry (ESI-MS) and matrix-assisted laser desorption/ ionization mass spectrometry (MALDI-MS). ESI-MS and MALDI-MS were proved to be appropriate techniques for identification of the substituted hydrolysis products, for which there are no standard compounds available. No highly substituted oligomers were found in the hydrolysates, which was taken as an indication of a more or less homogeneous distribution of cationic groups in the amylopectin molecules. Furthermore, from the results obtained it was suggested that the enzymes cleave glucosidic linkages only between unsubstituted glucose units and, preferentially, linkages in sequences containing more than two adjacent unsubstituted units. The determination of the amount of unsubstituted glucose produced from every successive hydrolysis step revealed slight differences between the different starch samples with respect to the homogeneity of the substitution pattern. Among the three samples under investigation, starch cationized in solution was found to have the most and dry-cationized starch the least homogeneous distribution of substituents.
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| 3. |
- Abou-Hachem, Maher, et al.
(författare)
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The modular organisation and stability of a thermostable family 10 xylanase
- 2003
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 21:5-6, s. 253-260
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Tidskriftsartikel (refereegranskat)abstract
- The thermophilic marine bacterium Rhodothermus marinus produces a modular family 10 xylanase (Xyn10A). It consists of two N-terminal family 4 carbohydrate binding modules (CBMs) followed by a domain of unknown function (D3), and a catalytic module (CM) flanked by a small fifth domain (D5) at its C-terminus. Several truncated mutants of the enzyme have been produced and characterised with respect to biochemical properties and stability. Multiple calcium binding sites are shown to be present in the two N-terminal CBMs and recent evidence suggests that the third domain of the enzyme also has the ability to bind the same metal ligand. The specific binding of Ca2+ was demonstrated to have a pronounced effect on thermostability as shown by differential scanning calorimetry and thermal inactivation studies. Furthermore, deletion mutants of the enzyme were less stable than the full-length enzyme suggesting that module interactions contributed to the stability of the enzyme. Finally, recent evidence indicates that the fifth domain of Xyn10A is a novel type of module mediating cell-attachment.
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| 4. |
- Anderson, Leif G, 1951, et al.
(författare)
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Enhanced uptake of atmospheric CO
- 2004
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Ingår i: Journal of Geophysical Research. ; 109:C06004
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Tidskriftsartikel (refereegranskat)abstract
- The waters of Storfjorden, a fjord in southern Svalbard, were investigated in late April 2002. The temperature was at the freezing point throughout the water column; the salinity in the top 30 m was just above 34.8, then increased nearly linearly to about 35.8 at the bottom. Nutrient and oxygen concentrations showed a minimal trend all through the water column, indicating minimal decay of organic matter. Normalized dissolved inorganic carbon, fCO2, and CFCs increase with depth below the surface mixed layer, while pH decreases. In waters below 50 m, there was an increase in dissolved inorganic carbon, corrected for decay of organic matter using the phosphate profile, corresponding to about 9 g C m−2 relative to the surface water concentration. We suggest this excess is a result of enhanced air-sea exchange of CO2 caused by sea ice formation. This enhancement is suggested to be a result of an efficient exchange through the surface film during the ice crystal formation and the rapid transport of the high salinity brine out of the surface layer.
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| 5. |
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| 6. |
- Anderson, Leif G, 1951, et al.
(författare)
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Variability in river runoff distribution in the Eurasian Basin of the Arctic Ocean
- 2004
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Ingår i: Journal of Geophysical Research-Oceans. - 0148-0227. ; 109:C1
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of freshwater within the Arctic Ocean and its export from it are intimately involved in climate and climate change processes both within and outside the Arctic Ocean. River runoff in the Arctic Ocean constitutes a major part of the Arctic Ocean freshwater budget. Within the Arctic Ocean, variability in the distribution of river runoff will be reflected in the location of the cold halocline that isolates the sea ice from the warm Atlantic Layer. Outside the Arctic Ocean, such variability will impact on the salinity of North Atlantic waters (Great Salinity Anomaly) and on deep convection areas of the North Atlantic Ocean, and thereby potentially on global thermohaline circulation. Rivers entering the Arctic Ocean have high levels of total alkalinity that contribute significantly to the total alkalinity of the surface Polar Mixed Layer. We exploit total alkalinity data to trace river runoff in the surface Polar Mixed Layer and to observe variability in the river runoff distribution in the Eurasian Basin over the period 1987-2001. The river runoff front changed from a position over the Gakkel Ridge in 1987 and 1991 to over the Lomonosov Ridge in 1996, and returned to a midpoint between the two ridges in 2001. Wind field changes as characterized by the Arctic Oscillation index are considered to be a major factor in determining ice and surface water flow. We note a correlation with 4-6 years delay between changes in river runoff distribution and the Arctic Oscillation index. We show that the delay can be inferred from a geostrophic flow calculation.
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| 7. |
- Astrand, Annika, et al.
(författare)
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Mice lacking melanin-concentrating hormone receptor 1 demonstrate increased heart rate associated with altered autonomic activity.
- 2004
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Ingår i: American journal of physiology. Regulatory, integrative and comparative physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 287:4
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Tidskriftsartikel (refereegranskat)abstract
- Melanin-concentrating hormone (MCH) plays an important role in energy balance. The current studies were carried out on a new line of mice lacking the rodent MCH receptor (MCHR1(-/-) mice). These mice confirmed the previously reported lean phenotype characterized by increased energy expenditure and modestly increased caloric intake. Because MCH is expressed in the lateral hypothalamic area, which also has an important role in the regulation of the autonomic nervous system, heart rate and blood pressure were measured by a telemetric method to investigate whether the increased energy expenditure in these mice might be due to altered autonomic nervous system activity. Male MCHR1(-/-) mice demonstrated a significantly increased heart rate [24-h period: wild type 495 +/- 4 vs. MCHR1(-/-) 561 +/- 8 beats/min (P < 0.001); dark phase: wild type 506 +/- 8 vs. MCHR1(-/-) 582 +/- 9 beats/min (P < 0.001); light phase: wild type 484 +/- 13 vs. MCHR1(-/-) 539 +/- 9 beats/min (P < 0.005)] with no significant difference in mean arterial pressure [wild type 110 +/- 0.3 vs. MCHR1(-/-) 113 +/- 0.4 mmHg (P > 0.05)]. Locomotor activity and core body temperature were higher in the MCHR1(-/-) mice during the dark phase only and thus temporally dissociated from heart rate differences. On fasting, wild-type animals rapidly downregulated body temperature and heart rate. MCHR1(-/-) mice displayed a distinct delay in the onset of this downregulation. To investigate the mechanism underlying these differences, autonomic blockade experiments were carried out. Administration of the adrenergic antagonist metoprolol completely reversed the tachycardia seen in MCHR1(-/-) mice, suggesting an increased sympathetic tone.
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| 8. |
- Baguma, Yona, et al.
(författare)
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Expression patterns of the gene encoding starch branching enzyme II in the storage roots of cassava (Manihot esculenta Crantz)
- 2003
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Ingår i: Plant Science. - 0168-9452 .- 1873-2259. ; 164:5, s. 833-839
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Tidskriftsartikel (refereegranskat)abstract
- Spatial and temporal expression patterns of the sbeII and sbeI genes, encoding starch branching enzyme II and I, respectively, in cassava (Manihot esculenta Crantz) were studied at different phenological stages of the crop. A partial cDNA for sbeII in cassava was cloned and used along with a cDNA-specific fragment of sbeI. As the cassava plant aged, the transcriptional activity of the sbeII and sbeI genes in the underground storage roots increased, whereas the activity in other organs remained the same or declined. At 180 days after planting (d.a.p.), levels of sbeII and sbeI transcripts in storage roots were very low, whereas at 360 d.a.p., the levels had increased dramatically. The 360 d.a.p. old storage roots also accumulated gbssII and gbssI transcripts, as well as a longer gbssI transcript, gbssI′. The difference between the gbssI and gbssI′ transcripts was shown to be due to differential splicing, whereby the gbssI′ transcript retained the first three introns. Unexpectedly, expression of sbeII and sbeI in the 360 d.a.p. storage roots exhibited fluctuations during the 24 h cycle, both under the normal light/dark regime and under continuous light or continuous dark conditions.
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| 9. |
- Bergqvist, Anders, et al.
(författare)
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The Hepatitis C Virus Core Protein Modulates T Cell Responses by Inducing Spontaneous and Altering T-cell Receptor-triggered Ca2+ Oscillations
- 2003
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Ingår i: Journal of Biological Chemistry. - : ASBMB. - 0021-9258 .- 1083-351X. ; 278:21, s. 18877-18883
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Tidskriftsartikel (refereegranskat)abstract
- Alterations of cytokine responses are thought to favor the establishment of persistent hepatitis C virus (HCV) infection, enhancing the risk of liver cirrhosis and hepatocellular carcinoma. Expression of the HCV core (C) protein modulates transcription of the IL-2 promoter in T lymphocytes by activating the nuclear factor of activated T lymphocyte (NFAT) pathway. Here we report on the effect of HCV C on Ca2+ signaling, which is essential for activation of NFAT. Expression of HCV C correlated with increased levels of cytosolic Ca2+ and spontaneous Ca2+ oscillations in transfected Jurkat cells. Triggering of the T-cell receptor induced a prolonged Ca2+ response characterized by vigorous high frequent oscillations in a high proportion of the responding cells. This was associated with decreased sizes and accelerated emptying of the intracellular calcium stores. The effect of HCV C on calcium mobilization was not dependent on phospholipase C-1 (PLC-) activity or increased inositol 1,4,5-trisphosphate (IP3) production and did not require functional IP3 receptors, suggesting that insertion of the viral protein in the endoplasmic reticulum membrane may be sufficient to promote Ca2+ leakage with dramatic downstream consequences on the magnitude and duration of the response. Our data suggest that expression of HCV C in infected T lymphocytes may contribute to the establishment of persistent infections by inducing Ca2+ oscillations that regulate both the efficacy and information content of Ca2+ signals and are ultimately responsible for induction of gene expression and functional differentiation.
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| 10. |
- Bill, Roslyn M., et al.
(författare)
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Analysis of the pore of the unusual major intrinsic protein channel, yeast Fps1p.
- 2001
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Ingår i: The Journal of biological chemistry. - 0021-9258 .- 1083-351X. ; 276:39, s. 36543-9
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Tidskriftsartikel (refereegranskat)abstract
- Fps1p is a glycerol efflux channel from Saccharomyces cerevisiae. In this atypical major intrinsic protein neither of the signature NPA motifs of the family, which are part of the pore, is preserved. To understand the functional consequences of this feature, we analyzed the pseudo-NPA motifs of Fps1p by site-directed mutagenesis and assayed the resultant mutant proteins in vivo. In addition, we took advantage of the fact that the closest bacterial homolog of Fps1p, Escherichia coli GlpF, can be functionally expressed in yeast, thus enabling the analysis in yeast cells of mutations that make this typical major intrinsic protein more similar to Fps1p. We observed that mutations made in Fps1p to "restore" the signature NPA motifs did not substantially affect channel function. In contrast, when GlpF was mutated to resemble Fps1p, all mutants had reduced activity compared with wild type. We rationalized these data by constructing models of one GlpF mutant and of the transmembrane core of Fps1p. Our model predicts that the pore of Fps1p is more flexible than that of GlpF. We discuss the fact that this may accommodate the divergent NPA motifs of Fps1p and that the different pore structures of Fps1p and GlpF may reflect the physiological roles of the two glycerol facilitators.
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