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871.
Rumpel S Lakshmi R Becker S Zweckstetter M 《Protein science : a publication of the Protein Society》2008,17(11):2015-2019
The X-ray structure of the homodimeric chaperone CesT is the only structure among the type three secretion system (TTSS) chaperones that shows a domain swap. This swap has potential importance for the mechanism of effector translocation through a TTSS. Here we present two nuclear magnetic resonance strategies exploiting pre-existing structural models and residual dipolar couplings (RDCs), which reveal the unswapped 35.4-kDa dimer to be present in solution. Particularly efficient is the discrimination of a swapped and unswapped structural state performed simultaneously to automatic backbone assignment using only HN-RDCs and carbonyl backbone chemical shifts. This direct approach may prove to be generally useful to rapidly differentiate two structural models. 相似文献
872.
Bahlawane C McIntosh M Krol E Becker A 《Molecular plant-microbe interactions : MPMI》2008,21(11):1498-1509
In order to enter symbiosis with its legume partner, Sinorhizobium meliloti requires regulatory systems for the appropriate responses to its environment. For example, motility is required for the chemotactic movement of bacteria toward the compounds released by its host, and exopolysaccharides (EPS) are required for bacterial attachment to the root or for invasion of the infection thread. Previous research has shown that ExoR/ExoS/ChvI as well as the ExpR/Sin quorum-sensing system inversely regulate both motility and EPS production, although the regulation mechanisms were unknown. We were able to attribute the ExpR-mediated regulation of motility to the ability of ExpR to bind a DNA sequence upstream of visN when activated by N-acyl-homoserine lactone. Furthermore, MucR, previously characterized as a regulator of EPS production, also affected motility. MucR inhibited expression of rem encoding an activator of motility gene expression and, consequently, the expression of Rem-regulated genes such as flaF and flgG. Binding of MucR to the rem promoter region was demonstrated and a sequence motif similar to the previously identified MucR binding consensus was identified within this region. The swarming ability of S. meliloti Rm2011 was shown to depend on a functional ExpR/Sin quorum-sensing system and the production of both flagella and EPS. Finally, we propose a model for the coordination of motility and EPS synthesis in S. meliloti. 相似文献
873.
The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti possesses the Sin quorum-sensing system based on N-acyl homoserine lactones (AHLs) as signal molecules. The Sin system consists of SinI, the AHL synthase, and SinR, the LuxR-type regulator. This system regulates the expression of a multitude of S. meliloti genes through ExpR, another LuxR-type regulator. Analysis of the activity of the sinI promoter showed that the expression of sinI is dependent on sinR and enhanced by a combination of expR and Sin AHLs. The characterization of the ExpR binding site upstream of sinI and the identification of binding sites upstream of the galactoglucan biosynthesis genes wgaA (expA1) and wgeA (expE1) allowed the definition of a consensus sequence for these binding sites. Based on this consensus, two additional ExpR binding sites in the promoter regions of exoI and exsH, two genes related to the production of succinoglycan, were found. The specific binding of ExpR to the wgaA and wgeA promoters was enhanced in the presence of oxo-C(14)-HL. Positive regulation of the galactoglucan biosynthesis genes by ExpR was shown to be dependent on WggR (ExpG) and influenced by MucR, both of which are previously characterized regulators of these genes. Based on these results, a reworked model of the Sin-ExpR quorum-sensing regulation scheme of galactoglucan production in S. meliloti is suggested. 相似文献
874.
875.
Du G Fischer BE Voss KO Becker G Taucher-Scholz G Kraft G Thiel G 《Radiation research》2008,170(3):316-326
Du, G., Fischer, B. E., Voss, K.-O., Becker, G., Taucher-Scholz, G., Kraft, G. and Thiel, G. The Absence of an Early Calcium Response to Heavy-Ion Radiation in Mammalian Cells. Radiat. Res. 170, 316-326 (2008).Intracellular calcium is an important second messenger that regulates many cell functions. Recent studies have shown that calcium ions can also regulate the cellular responses to ionizing radiation. However, previous data are restricted to cells treated with low-LET radiations (X rays, gamma rays and beta particles). In this work, we investigated the calcium levels in cells exposed to heavy-ion radiation of high LET. The experiments were performed at the single ion hit facility of the GSI heavy-ion microprobe. Using a built-in online calcium imaging system, the intracellular calcium concentrations were examined in HeLa cells and human foreskin fibroblast AG1522-D cells before and after irradiation with 4.8 MeV/nucleon carbon or argon ions. Although the experiment was sensitive enough to detect the calcium response to other known stimuli, no response to heavy-ion radiation was found in these two cell types. We also found that heavy-ion radiation has no impact on calcium oscillation induced by hypoxia stress in fibroblast cells. 相似文献
876.
The assembly and budding of a new virus is a fundamental step in retroviral replication. Yet, despite substantial progress in the structural and biochemical characterization of retroviral budding, the underlying physical mechanism remains poorly understood, particularly with respect to the mechanism by which the virus overcomes the energy barrier associated with the formation of high membrane curvature during viral budding. Using atomic force, fluorescence, and transmission electron microscopy, we find that both human immunodeficiency virus and Moloney murine leukemia virus remodel the actin cytoskeleton of their host. These actin-filamentous structures assemble simultaneously with or immediately after the beginning of budding, and disappear as soon as the nascent virus is released from the cell membrane. Analysis of sections of cryopreserved virus-infected cells by transmission electron microscopy reveals similar actin filament structures emerging from every nascent virus. Substitution of the nucleocapsid domain implicated in actin binding by a leucine-zipper domain results in the budding of virus-like particles without remodeling of the cell's cytoskeleton. Notably, viruses carrying the modified nucleocapsid domains bud more slowly by an order of magnitude compared to the wild-type. The results of this study show that retroviruses utilize the cell cytoskeleton to expedite their assembly and budding. 相似文献
877.
Background
Visceral fat (VF) accretion is a hallmark of aging in humans. Epidemiologic studies have implicated abdominal obesity as a major risk factor for insulin resistance, type 2 diabetes, cardiovascular disease, metabolic syndrome and death.Methods
Studies utilizing novel rodent models of visceral obesity and surgical strategies in humans have been undertaken to determine if subcutaneous (SC) abdominal or VF are causally linked to age-related diseases.Results
Specific depletion or expansion of the VF depot using genetic or surgical tools in rodents has been shown to have direct effects on disease risk. In contrast, surgically removing large quantities of SC fat does not consistently improve metabolic parameters in humans or rodents, while benefits were observed with SC fat expansion in mice, suggesting that SC fat accrual is not an important contributor to metabolic decline. There is also compelling evidence in humans that abdominal obesity is a stronger risk factor for mortality risk than general obesity. Likewise, we have shown that surgical removal of VF improves mean and maximum lifespan in rats, providing the first causal evidence that VF depletion may be an important underlying cause of improved lifespan with caloric restriction.General significance
This review provides both corollary and causal evidence for the importance of accounting for body fat distribution, and specifically VF, when assessing disease and mortality risk. Given the hazards of VF accumulation on health, treatment strategies aimed at selectively depleting VF should be considered as a viable tool to effectively reduce disease risk in humans. 相似文献878.
Immunogenicity of HLA-A1-restricted peptides derived from S100A4 (metastasin 1) in melanoma patients
Valeska Hofmeister-Mueller Claudia S. Vetter-Kauczok Ramona Ullrich Katharina Meder Eugene Lukanidin Eva-Bettina Broecker Per thor Straten Mads Hald Andersen David Schrama Juergen C. Becker 《Cancer immunology, immunotherapy : CII》2009,58(8):1265-1273
S100A4 (metastasin 1) belongs to the S100 family of Ca2+ binding proteins. While not present in most differentiated adult tissues, S100A4 is upregulated in the micromilieu of tumors.
It is primarily expressed by tumor-associated macrophages, fibroblasts, and tumor endothelial cells. Due to its strong induction
in tumors S100A4 is a promising target for cancer immunotherapy. By reverse immunology, using epitope prediction programs,
we identified 3 HLA-A1-restricted peptide epitopes (S100A4 A1-1, A1-2, and A1-3) which are subject to human T cell responses
as detected in peripheral blood of melanoma patients by means of IFN-γ ELISPOT and cytotoxicity assays. In addition, IFN-γ
responses to S100A4 A1-2 can not only be induced by stimulation of T cells with peptide-loaded DC but also by stimulation
with S100A4 protein-loaded DC, indicating that this epitope is indeed generated by processing of the endogenously expressed
protein. In addition, S100A4 A1-2 reactive T cells demonstrate lysis of HLA-A1+ fibroblasts in comparison to HLA-A1− fibroblasts. In summary, this HLA-A1-restricted peptide epitope is a candidate for immunotherapeutical approaches targeting
S100A4-expressing cells in the tumor stroma. 相似文献
879.
880.
Judith Becker Corinna Klopprogge Hartwig Schr?der Christoph Wittmann 《Applied and environmental microbiology》2009,75(24):7866-7869
In the present work, lysine production by Corynebacterium glutamicum was improved by metabolic engineering of the tricarboxylic acid (TCA) cycle. The 70% decreased activity of isocitrate dehydrogenase, achieved by start codon exchange, resulted in a >40% improved lysine production. By flux analysis, this could be correlated to a flux shift from the TCA cycle toward anaplerotic carboxylation.With an annual market volume of more than 1,000,000 tons, lysine is one of the dominating products in biotechnology. In recent years, rational metabolic engineering has emerged as a powerful tool for lysine production (16, 18, 22). Hereby, different target enzymes and pathways in the central metabolism could be identified and successfully modified to create superior production strains (1, 2, 5, 8, 10, 17-20). The tricarboxylic acid (TCA) cycle has not been rationally engineered so far, despite its major role in Corynebacterium glutamicum (6). From metabolic flux studies, however, it seems that the TCA cycle might offer a great potential for optimization (Fig. (Fig.1),1), which is also predicted from in silico pathway analysis (13, 22). Experimental evidence comes from studies with Brevibacterium flavum exhibiting increased lysine production due to an induced bottleneck toward the TCA cycle (21). In the present work, we performed TCA cycle engineering by downregulation of isocitrate dehydrogenase (ICD). ICD is the highest expressed TCA cycle enzyme in C. glutamicum (7). Downregulation was achieved by start codon exchange, controlling ICD expression on the level of translation.Open in a separate windowFIG. 1.Stoichiometric correlation of lysine yield (%), biomass yield (g/mol) and TCA cycle flux (%; entry flux through citrate synthase) determined by 13C metabolic flux analysis achieved by paraboloid fitting of the data set (parameters were determined with Y0 = 105.1, a = −1.27, b = 0.35, c = −9.35 × 10−3, d = −11.16 × 10−3). The data displayed represent values from 18 independent experiments with different C. glutamicum strains taken from previous studies (1-3, 11, 12, 15, 23). 相似文献