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Bacterial flagellar diversity in the post-genomic era 总被引:1,自引:0,他引:1
Flagellar biosynthesis has been studied most thoroughly in laboratory strains of Escherichia coli and Salmonella enterica. However, genome sequencing has uncovered flagellar loci in distantly related bacteria. We have used homology searches to determine how far the E. coli/S. enterica paradigm can be generalised to other flagellar systems. Numerous previously unrecognized homologues of flagellar components were discovered, including novel FlgM, FlgN, FliK and FliO homologues. Homology was found between the FliK proteins and a molecular ruler, YscP, from a virulence-associated type-III secretion system. Also described is a new family of flagellar proteins, the FlhX proteins, which resemble the cytoplasmic domain of FlhB. 相似文献
44.
Lu Z Feng X Song L Han Y Kim A Herzberg O Woodson WR Martin BM Mariano PS Dunaway-Mariano D 《Biochemistry》2005,44(50):16365-16376
The work described in this paper was carried out to define the chemical function a new member of the isocitrate lyase enzyme family derived from the flowering plant Dianthus caryophyllus. This protein (Swiss-Prot entry Q05957) is synthesized in the senescent flower petals and is named the "petal death protein" or "PDP". On the basis of an analysis of the structural contexts of sequence markers common to the C-C bond lyases of the isocitrate lyase/phosphoenolpyruvate mutase superfamily, a substrate screen that employed a (2R)-malate core structure was designed. Accordingly, stereochemically defined C(2)- and C(3)-substituted malates were synthesized and tested as substrates for PDP-catalyzed cleavage of the C(2)-C(3) bond. The screen identified (2R)-ethyl, (3S)-methylmalate, and oxaloacetate [likely to bind as the hydrate, C(2)(OH)(2) gem-diol] as the most active substrates (for each, k(cat)/K(m) = 2 x 10(4) M(-)(1) s(-)(1)). In contrast to the stringent substrate specificities previously observed for the Escherichia coli isocitrate and 2-methylisocitrate lyases, the PDP tolerated hydrogen, methyl, and to a much lesser extent acetate substituents at the C(3) position (S configuration only) and hydoxyl, methyl, ethyl, propyl, and to a much lesser extent isobutyl substituents at C(2) (R configuration only). It is hypothesized that PDP functions in oxalate production in Ca(2+) sequestering and/or in carbon scavenging from alpha-hydroxycarboxylate catabolites during the biochemical transition accompanying petal senescence. 相似文献
45.
Allen IC Hartney JM Coffman TM Penn RB Wess J Koller BH 《American journal of physiology. Lung cellular and molecular physiology》2006,290(3):L526-L533
Thromboxane A2 (TXA2) is a potent lipid mediator released by platelets and inflammatory cells and is capable of inducing vasoconstriction and bronchoconstriction. In the airways, it has been postulated that TXA2 causes airway constriction by direct activation of thromboxane prostanoid (TP) receptors on airway smooth muscle cells. Here we demonstrate that although TXA2 can mediate a dramatic increase in airway smooth muscle constriction and lung resistance, this response is largely dependent on vagal innervation of the airways and is highly sensitive to muscarinic acetylcholine receptor (mAChR) antagonists. Further analyses employing pharmacological and genetic strategies demonstrate that TP-dependent changes in lung resistance and airway smooth muscle tension require expression of the M2 mAChR subtype. These results raise the possibility that some of the beneficial actions of anticholinergic agents used in the treatment of asthma and chronic obstructive pulmonary disease result from limiting physiological changes mediated through the TP receptor. Furthermore, these findings demonstrate a unique pathway for TP regulation of homeostatic mechanisms in the airway and suggest a paradigm for the role of TXA2 in other organ systems. 相似文献
46.
Charles Williams Seok-Hyung Kim Terri T. Ni Lauren Mitchell Hyunju Ro John S. Penn Scott H. Baldwin Lila Solnica-Krezel Tao P. Zhong 《Developmental biology》2010,341(1):196-391
In vertebrate embryos, the dorsal aorta and the posterior cardinal vein form in the trunk to comprise the original circulatory loop. Previous studies implicate Hedgehog (Hh) signaling in the development of the dorsal aorta. However, the mechanism controlling specification of artery versus vein remains unclear. Here, we investigated the cell-autonomous mechanism of Hh signaling in angioblasts (endothelial progenitor cells) during arterial-venous specification utilizing zebrafish mutations in Smoothened (Smo), a G protein-coupled receptor essential for Hh signaling. smo mutants exhibit an absence of the dorsal aorta accompanied by a reciprocal expansion of the posterior cardinal vein. The increased number of venous cells is equivalent to the loss of arterial cells in embryos with loss of Smo function. Activation of Hh signaling expands the arterial cell population at the expense of venous cell fate. Time-lapse imaging reveals two sequential waves of migrating progenitor cells that contribute to the dorsal aorta and the posterior cardinal vein, respectively. Angioblasts deficient in Hh signaling fail to contribute to the arterial wave; instead, they all migrate medially as a single population to form the venous wave. Cell transplantation analyses demonstrate that Smo plays a cell-autonomous role in specifying angioblasts to become arterial cells, and Hh signaling-depleted angioblasts differentiate into venous cells instead. Collectively, these studies suggest that arterial endothelial cells are specified and formed via repressing venous cell fate at the lateral plate mesoderm by Hh signaling during vasculogenesis. 相似文献
47.
Horton H Frank I Baydo R Jalbert E Penn J Wilson S McNevin JP McSweyn MD Lee D Huang Y De Rosa SC McElrath MJ 《Journal of immunology (Baltimore, Md. : 1950)》2006,177(10):7406-7415
HIV-1-infected persons with HLA-B27 and -B57 alleles commonly remain healthy for decades without antiretroviral therapy. Properties of CD8+ T cells restricted by these alleles considered to confer disease protection in these individuals are elusive but important to understand and potentially elicit by vaccination. To address this, we compared CD8+ T cell function induced by HIV-1 immunogens and natural infection using polychromatic flow cytometry. HIV-1-specific CD8+ T cells from all four uninfected immunized and 21 infected subjects secreted IFN-gamma and TNF-alpha. However, CD8+ T cells induced by vaccination and primary infection, but not chronic infection, proliferated to their cognate epitopes. Notably, B27- and B57-restricted CD8+ T cells from nonprogressors exhibited greater expansion than those restricted by other alleles. Hence, CD8+ T cells restricted by certain protective alleles can resist replicative defects, which permits expansion and antiviral effector activities. Our findings suggest that the capacity to maintain CD8+ T cell proliferation, regardless of MHC-restriction, may serve as an important correlate of disease protection in the event of infection following vaccination. 相似文献
48.
49.
Yang R Chen JY Xi N Lai KW Qu C Fung CK Penn LS Xi J 《Experimental cell research》2012,318(5):521-526
Cell signaling often causes changes in cellular mechanical properties. Knowledge of such changes can ultimately lead to insight into the complex network of cell signaling. In the current study, we employed a combination of atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) to characterize the mechanical behavior of A431 cells in response to epidermal growth factor receptor (EGFR) signaling. From AFM, which probes the upper portion of an individual cell in a monolayer of cells, we observed increases in energy dissipation, Young's modulus, and hysteresivity. Increases in hysteresivity imply a shift toward a more fluid-like mechanical ordering state in the bodies of the cells. From QCM-D, which probes the basal area of the monolayer of cells collectively, we observed decreases in energy dissipation factor. This result suggests a shift toward a more solid-like state in the basal areas of the cells. The comparative analysis of these results indicates a regionally specific mechanical behavior of the cell in response to EGFR signaling and suggests a correlation between the time-dependent mechanical responses and the dynamic process of EGFR signaling. This study also demonstrates that a combination of AFM and QCM-D is able to provide a more complete and refined mechanical profile of the cells during cell signaling. 相似文献
50.
Bacteria and nutrients were determined in upper soil samples collected underneath and between canopies of the dominant perennial
in each of three sites along a steep precipitation gradient ranging from the Negev desert in the south of Israel to a Mediterranean
forest in the north. Bacterial abundance, monitored by phospholipid fatty acid analysis, was significantly higher under the
shrub canopy (compared to barren soils) in the arid and semi-arid sites but not in the Mediterranean soils. Bacterial community
composition, determined using terminal restriction fragment length polymorphism and clone libraries, differed according to
the sample’s origin. Closer examination revealed that in the arid and semi-arid sites, α-Proteobacteria are more abundant
under the shrub canopy, while barren soils are characterized by a higher abundance of Actinobacteria. The bacterial communities
in the Mediterranean soils were similar in both patch types. These results correspond to the hypothesis of “resource islands”,
suggesting that shrub canopies provide a resource haven in low-resource landscapes. Yet, a survey of the physicochemical parameters
of inter- and under-shrub soils could not attribute the changes in bacterial diversity to soil moisture, organic matter, or
essential macronutrients. We suggest that in the nutrient-poor soils of the arid and semi-arid sites, bacteria occupying the
soil under the shrub canopy may have longer growth periods under favorable conditions, resulting in their increased biomass
and altered community composition. 相似文献