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51.
Specific bonds between an iron oxide surface and outer membrane cytochromes MtrC and OmcA from Shewanella oneidensis MR-1 下载免费PDF全文
Lower BH Shi L Yongsunthon R Droubay TC McCready DE Lower SK 《Journal of bacteriology》2007,189(13):4944-4952
Shewanella oneidensis MR-1 is purported to express outer membrane cytochromes (e.g., MtrC and OmcA) that transfer electrons directly to Fe(III) in a mineral during anaerobic respiration. A prerequisite for this type of reaction would be the formation of a stable bond between a cytochrome and an iron oxide surface. Atomic force microscopy (AFM) was used to detect whether a specific bond forms between a hematite (Fe(2)O(3)) thin film, created with oxygen plasma-assisted molecular beam epitaxy, and recombinant MtrC or OmcA molecules coupled to gold substrates. Force spectra displayed a unique force signature indicative of a specific bond between each cytochrome and the hematite surface. The strength of the OmcA-hematite bond was approximately twice that of the MtrC-hematite bond, but direct binding to hematite was twice as favorable for MtrC. Reversible folding/unfolding reactions were observed for mechanically denatured MtrC molecules bound to hematite. The force measurements for the hematite-cytochrome pairs were compared to spectra collected for an iron oxide and S. oneidensis under anaerobic conditions. There is a strong correlation between the whole-cell and pure-protein force spectra, suggesting that the unique binding attributes of each cytochrome complement one another and allow both MtrC and OmcA to play a prominent role in the transfer of electrons to Fe(III) in minerals. Finally, by comparing the magnitudes of binding force for the whole-cell versus pure-protein data, we were able to estimate that a single bacterium of S. oneidensis (2 by 0.5 microm) expresses approximately 10(4) cytochromes on its outer surface. 相似文献
52.
E. S. Lower 《BMJ (Clinical research ed.)》1946,1(4446):447-448
53.
Groups of pregnant Sprague-Dawley rats were treated orally with procarbazine, an antineoplastic drug, at dose levels of 0, 1.0, 2.5, 5.0, 7.5, and 10.0 mg/kg/day from days 12 through 15 of gestation. Following normal delivery, offspring were raised until day 21 and sacrificed, and their brains removed and weighed. A dose-dependent micrencephaly, characterized by hypoplasia of the cerebral hemispheres, was seen starting at 2.5 mg/kg/day. In a second study, groups of pregnant female rats were given a single dose of 10 mg/kg procarbazine on gestation day 12, 13, 14, or 15. Micrencephaly occurred in 21-day-old offspring from all groups, with the greatest effect induced on days 13, 14 and 15. Analysis of brain region weights revealed a maximum reduction in neocortex weight in offspring from groups treated on days 13 and 14. The hippocampus, cerebellum, and diencephalon-midbrain were also reduced in size, depending on the day of treatment, while the corpus striatum and pons-medulla were spared. In a final study, embryos from females treated on gestation days 12 through 15 were removed, fixed, and sectioned at 24-hour intervals starting on gestation days 13. Necrosis and cellular degeneration were observed with decreasing severity in the telencephalon, diencephalon, mesencephalon, and medulla. The neocortex of 20-day treated fetuses was characterized by a thickening of the ventricular zone and reduced cellularity of the cortical plate. 相似文献
54.
Molecular evolution of a multigene family in group A streptococci 总被引:15,自引:0,他引:15
The emm genes are members of a gene family in group A streptococci (GAS)
that encode for antiphagocytic cell-surface proteins and/or
immunoglobulin-binding proteins. Previously sequenced genes in this family
have been named "emm," "fcrA," "enn," "arp," "protH," and "mrp"; herein
they will be referred to as the "emm gene family." The genes in the emm
family are located in a cluster occupying 3-6 kb between the genes mry and
scpA on the chromosome of Streptococcus pyogenes. Most GAS strains contain
one to three tandemly arranged copies of emm-family genes in the cluster,
but the alleles within the cluster vary among different strains.
Phylogenetic analysis of the conserved sequences at the 3' end of these
genes differentiates all known members of this family into four
evolutionarily distinct emm subfamilies. As a starting point to analyze how
the different subfamilies are related evolutionarily, the structure of the
emm chromosomal region was mapped in a number of diverse GAS strains by
using subfamily-specific primers in the polymerase chain reaction. Nine
distinct chromosomal patterns of the genes in the emm gene cluster were
found. These nine chromosomal patterns support a model for the evolution of
the emm gene family in which gene duplication followed by sequence
divergence resulted in the generation of four major-gene subfamilies in
this locus.
相似文献
55.
The membrane-associated protein-serine/threonine kinase from Sulfolobus solfataricus is a glycoprotein 下载免费PDF全文
Treatment of a sodium dodecyl sulfate-polyacrylamide gel with periodic acid-Schiff (PAS) stain or blotting with Galanthus nivalis agglutinin revealed the presence of several glycosylated polypeptides in a partially purified detergent extract of the membrane fraction of Sulfolobus solfataricus. One of the glycoproteins comigrated with the membrane-associated protein-serine/threonine kinase from S. solfataricus, which had been radiolabeled by autophosphorylation with [(32)P]ATP in vitro. Treatment with a chemical deglycosylating agent, trifluoromethanesulfonic acid, abolished PAS staining and reduced the M(r) of the protein kinase from approximately 67,000 to approximately 62,000. Protein kinase activity also adhered to, and could be eluted from, agarose beads containing bound G. nivalis agglutinin. Glycosylation of the protein kinase implies that at least a portion of this integral membrane protein resides on the external surface of the cell membrane. 相似文献
56.
Magdalena Kaliszewska Jakub Kruszewski Biruta Kierdaszuk Anna Kostera-Pruszczyk Monika Nojszewska Anna Łusakowska Joel Vizueta Dorota Sabat Dorota Lutyk Michał Lower Dorota Piekutowska-Abramczuk Aneta Kaniak-Golik Ewa Pronicka Anna Kamińska Ewa Bartnik Paweł Golik Katarzyna Tońska 《Human genetics》2015,134(9):951-966
57.
Suzanne E Wahrle Aarti R Shah Anne M Fagan Scott Smemo John SK Kauwe Andrew Grupe Anthony Hinrichs Kevin Mayo Hong Jiang Leon J Thal Alison M Goate David M Holtzman 《Molecular neurodegeneration》2007,2(1):1-9
Background
Animal studies suggest that brain apolipoprotein E (apoE) levels influence amyloid-β (Aβ) deposition and thus risk for Alzheimer's disease (AD). We have previously demonstrated that deletion of the ATP-binding cassette A1 transporter (ABCA1) in mice causes dramatic reductions in brain and cerebrospinal fluid (CSF) apoE levels and lipidation. To examine whether polymorphisms in ABCA1 affect CSF apoE levels in humans, we measured apoE in CSF taken from 168 subjects who were 43 to 91 years old and were either cognitively normal or who had mild AD. We then genotyped the subjects for ten previously identified ABCA1 single nucleotide polymorphisms (SNPs).Results
In all subjects, the mean CSF apoE level was 9.09 μg/ml with a standard deviation of 2.70 μg/ml. Levels of apoE in CSF samples taken from the same individual two weeks apart were strongly correlated (r2 = 0.93, p < 0.01). In contrast, CSF apoE levels in different individuals varied widely (coefficient of variation = 46%). CSF apoE levels did not vary according to AD status, APOE genotype, gender or race. Average apoE levels increased with age by ~0.5 μg/ml per 10 years (r2 = 0.05, p = 0.003). We found no significant associations between CSF apoE levels and the ten ABCA1 SNPs we genotyped. Moreover, in a separate sample of 1225 AD cases and 1431 controls, we found no association between the ABCA1 SNP rs2230806 and AD as has been previously reported.Conclusion
We found that CSF apoE levels vary widely between individuals, but are stable within individuals over a two-week interval. AD status, APOE genotype, gender and race do not affect CSF apoE levels, but average CSF apoE levels increase with age. Given the lack of association between CSF apoE levels and genotypes for the ABCA1 SNPs we examined, either these SNPs do not affect ABCA1 function or if they do, they do not have strong effects in the CNS. Finally, we find no evidence for an association between the ABCA1 SNP rs2230806 and AD in a large sample set. 相似文献58.
KLARA BJÖRG JAKOBSDÓTTIR þÓRA DÖGG JÖRUNDSDÓTTIR SIGURLAUG SKÍRNISDÓTTIR SIGRÍÐUR HJÖRLEIFSDÓTTIR GUÐMUNDUR Ó. HREGGVIÐSSON ANNA KRISTÍN DANÍELSDÓTTIR CHRISTOPHE PAMPOULIE 《Molecular ecology resources》2006,6(2):337-339
Nine out of 22 microsatellite primers tested were successfully amplified on three samples of cod Gadus morhua L. (two contemporary and one archived otolith samples). All loci were polymorphic (5–23 alleles/locus). The average observed heterozygosity across loci and samples was 0.625, ranging from 0.294 to 0.895 at each locus. All loci were under Hardy–Weinberg equilibrium, except PGmo56 that showed significant excess of heterozygotes in all studied samples. The isolated loci were suitable for degraded DNA and therefore useful for conducting a long‐term temporal study with DNA obtained from archived otoliths of cod. 相似文献
59.
目的减少Finn CA于1984年首次报道的小鼠月经模型的观察时间点,以期为月经生理学研究提供一种较廉价且易操作的月经模型。方法应用成年雌性去势C57BL/6小鼠,给予续贯性激素处理,最末次激素处理后4~6h,实验组小鼠宫腔内注射花生油以诱导子宫内膜蜕膜化反应,对照组小鼠给予同样激素处理但无宫腔油剂注射。分别于油剂处理后31~35h(T3组)、56~70h(T4组)处死小鼠,称量子宫湿重,制作H&E组织切片,运用图像分析软件CAST2,计算全子宫横截面积(TUA)与子宫内膜横截面积(EA)。结果H&E染色子宫组织切片示在单纯雌激素作用下宫内膜呈单层立方上皮,核浆比较高,内膜基质疏松;雌孕激素联合处理后,分泌细胞易见,腺腔内可见分泌物。激素撤退后实验组T3观察到子宫内膜剥离,T4组示子宫内膜修复。对照组子宫内膜始终完整。子宫湿重在激素撤退后,实验组下降较慢。激素撤退后实验组T3的TUA继续上升而EA则维持原水平,T4组TUA与EA均明显下降。结论此模型在子宫内膜剥落期和早期修复期组织学特征与人类子宫内膜有一定的相似性。 相似文献
60.
Metabolism of cationized lipoproteins by human fibroblasts: biochemical and morphologic correlations 下载免费PDF全文
Human plasma low density lipoprotein (LDL) that had been rendered polycationic by coupling with N, N-dimethyl-1, 3-propanediamine (DMPA) was shown by electron microscopy to bind in clusters to the surface of human fibroblasts. The clusters resembled those formed by polycationic ferritin (DMPA-feritin), a visual probe that binds to anionic site on the plasma membrane. Biochemical studies with (125)I-labeled DMPA-LDL showed that the membrane-bound lipoprotein was internalized and hydrolyzed in lysosomes. The turnover time for cell bound (125)I-DMPA-LDL, i.e., the time in which the amount of (125)I-DMPA-LDL degraded was equal to the steady-state cellular content of the lipoprotein, was about 50 h. Because the DMPA-LDL gained access to fibroblasts by binding nonspecifically to anionic sites on the cell surface rather than by binding to the physiologic LDL receptor, its uptake failed to be regulated under conditions in which the uptake of native LDL was reduced by feedback suppression of the LDL receptor. As a result, unlike the case with native LDL, the DMPA-LDL accumulated progressively within the cell, and this led to a massive increase in the cellular content of both free and esterified cholesterol. Studies with (14)C-oleate showed that at least 20 percent of the accumulated cholesteryl esters represented cholesterol that had been esterified within the cell. After 4 days of incubation with 10 μg/ml of DMPA-LDL, fibroblasts had accumulated so much cholesteryl ester that neutral lipid droplets were visible at the light microscope level with Oil Red O staining. By electron microscopy, these intracellular lipid droplets were observed to lack a tripartite limiting membrane. The ability to cause the overaccumulation of cholesteryl esters within cells by using DMPA-LDL provides a model system for study of the pathologic consequences at the cellular level of massive deposition of cholesteryl ester. 相似文献