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221.
222.
Chloride intracellular channel proteins (CLICs) differ from most ion channels as they can exist in both soluble and integral membrane forms. The CLICs are expressed as soluble proteins but can reversibly autoinsert into the membrane to form active ion channels. For CLIC1, the interaction with the lipid bilayer is enhanced under oxidative conditions. At present, little evidence is available characterizing the structure of the putative oligomeric CLIC integral membrane form. Previously, fluorescence resonance energy transfer (FRET) was used to monitor and model the conformational transition within CLIC1 as it interacts with the membrane bilayer. These results revealed a large-scale unfolding between the C- and N-domains of CLIC1 as it interacts with the membrane. In the present study, FRET was used to probe lipid-induced structural changes arising in the vicinity of the putative transmembrane region of CLIC1 (residues 24-46) under oxidative conditions. Intramolecular FRET distances are consistent with the model in which the N-terminal domain inserts into the bilayer as an extended α-helix. Further, intermolecular FRET was performed between fluorescently labeled CLIC1 monomers within membranes. The intermolecular FRET shows that CLIC1 forms oligomers upon oxidation in the presence of the membranes. Fitting the data to symmetric oligomer models of the CLIC1 transmembrane form indicates that the structure is large and most consistent with a model comprising approximately six to eight subunits. 相似文献
223.
224.
Rakic-Martinez M Drevets DA Dutta V Katic V Kathariou S 《Applied and environmental microbiology》2011,77(24):8714-8721
Listeria monocytogenes is a leading agent for severe food-borne illness and death in the United States and other nations. Even though drug resistance has not yet threatened therapeutic interventions for listeriosis, selective pressure associated with exposure to antibiotics and disinfectants may result in reduced susceptibility to these agents. In this study, selection of several L. monocytogenes strains on either ciprofloxacin (2 μg/ml) or the quaternary ammonium disinfectant benzalkonium chloride (BC; 10 μg/ml) led to derivatives with increased MICs not only to these agents but also to several other toxic compounds, including gentamicin, the dye ethidium bromide, and the chemotherapeutic drug tetraphenylphosphonium chloride. The spectrum of compounds to which these derivatives exhibited reduced susceptibility was the same regardless of whether they were selected on ciprofloxacin or on BC. Inclusion of strains harboring the large plasmid pLM80 revealed that MICs to ciprofloxacin and gentamicin did not differ between the parental and plasmid-cured strains. However, ciprofloxacin-selected derivatives of pLM80-harboring strains had higher MICs than those derived from the plasmid-cured strains. Susceptibility to the antimicrobials was partially restored in the presence of the potent efflux inhibitor reserpine. Taken together, these data suggest that mutations in efflux systems are responsible for the multidrug resistance phenotype of strains selected on ciprofloxacin or BC. 相似文献
225.
226.
The century-long research on succession has bestowed us with a number of theories, but little agreement on what causes species
replacements through time. The majority of studies has explored the temporal trends of individual species in plant and much
less so in microbial communities, arguing that interspecific interactions, especially competition, play a key role in community
organization throughout succession. In this experimental investigation of periphytic succession in re-circulating laboratory
streams, we examined the density and the relative abundance of diatoms and soft algae for 35 days across gradients of low
to high nutrient supply (nitrogen + phosphorus) and low to intermediate current velocity (10 vs. 30 cm·s−1). All algal species were classified into trophic groups and morphological guilds, both of which responded more strongly to
nutrient than current velocity manipulations, as shown by regression analyses. We concluded that within the manipulated environmental
ranges: (1) Succession was a gradient of stress tolerance, driven primarily by nutrient supply and secondarily, by current
velocity. Nutrient supply had a qualitative effect in determining whether the contribution of species tolerant vs. sensitive
to nutrient limitation would increase through time, while current velocity had a quantitative influence and affected only
the rate of this increase. (2) The mechanism of algal succession at a functional level was a neutral coexistence, whereby
the tolerant low profile guild maintained high density when overgrown by sensitive species, while sensitive species, constituting
mostly the motile and high profile guilds, were neither facilitated nor inhibited by tolerant species but controlled by the
environment. It is suggested that the mechanism of succession may depend on the level of biological organization with interspecific
interactions giving way to neutral coexistence along the hierarchy from species to functional groups. Considering that the
functional makeup is strictly environmentally defined, while species composition reflects local and regional species pools
that may exhibit substantial geographic variability, succession is deterministic at a functional level but stochastic at a
species level. 相似文献
227.
Microbial motility frequently depends on flagella or type?IV pili. Using recently developed archaeal genetic tools, archaeal flagella and its assembly machinery have been identified. Archaeal flagella are functionally similar to bacterial flagella and their assembly systems are homologous with type?IV pili assembly systems of Gram-negative bacteria. Therefore elucidating their biochemistry may result in insights in both archaea and bacteria. FlaI, a critical cytoplasmic component of the archaeal flagella assembly system in Sulfolobus acidocaldarius, is a member of the type?II/IV secretion system ATPase superfamily, and is proposed to be bi-functional in driving flagella assembly and movement. In the present study we show that purified FlaI is a Mn2+-dependent ATPase that binds MANT-ATP [2'-/3'-O-(N'- methylanthraniloyl)adenosine-5'-O-triphosphate] with a high affinity and hydrolyses ATP in a co-operative manner. FlaI has an optimum pH and temperature of 6.5 and 75?°C for ATP hydrolysis. Remarkably, archaeal, but not bacterial, lipids stimulated the ATPase activity of FlaI 3-4-fold. Analytical gel filtration indicated that FlaI undergoes nucleotide-dependent oligomerization. Furthermore, SAXS (small-angle X-ray scattering) analysis revealed an ATP-dependent hexamerization of FlaI in solution. The results of the present study report the first detailed biochemical analyses of the motor protein of an archaeal flagellum. 相似文献
228.
Hartung S Arvai AS Wood T Kolappan S Shin DS Craig L Tainer JA 《The Journal of biological chemistry》2011,286(51):44254-44265
Pilin proteins assemble into Type IV pili (T4P), surface-displayed bacterial filaments with virulence functions including motility, attachment, transformation, immune escape, and colony formation. However, challenges in crystallizing full-length fiber-forming and membrane protein pilins leave unanswered questions regarding pilin structures, assembly, functions, and vaccine potential. Here we report pilin structures of full-length DnFimA from the sheep pathogen Dichelobacter nodosus and FtPilE from the human pathogen Francisella tularensis at 2.3 and 1 ? resolution, respectively. The DnFimA structure reveals an extended kinked N-terminal α-helix, an unusual centrally located disulfide, conserved subdomains, and assembled epitopes informing serogroup vaccines. An interaction between the conserved Glu-5 carboxyl oxygen and the N-terminal amine of an adjacent subunit in the crystallographic dimer is consistent with the hypothesis of a salt bridge between these groups driving T4P assembly. The FtPilE structure identifies an authentic Type IV pilin and provides a framework for understanding the role of T4P in F. tularensis virulence. Combined results define a unified pilin architecture, specialized subdomain roles in pilus assembly and function, and potential therapeutic targets. 相似文献
229.
Sophia N. Sangiorgio Donald B. Longjohn Lawrence D. Dorr Edward Ebramzadeh 《Journal of biomechanics》2011,44(1):22-27
In this study, the in vitro fixation of four otherwise identical double-tapered stem-types, varying only in surface finish (polished or matte) and proximal stem geometry (with or without flanges) were compared under two conditions. First, four specimens of each stem type were tested with initially bonded stem–cement interfaces, representing early post-operative conditions. Then, simulating conditions a few weeks to months later, stems were implanted in unused synthetic femurs, with a thin layer coating the stem to prevent stem–cement adhesion. Per-cycle motions were measured at both cement interfaces throughout loading. Overall, surface finish had the smallest relative effect on fixation compared to flanges. Flanges increased axial fixation by 22 μm per-cycle, regardless of surface finish (P=0.01). Further, all stems moved under dynamic load at the stem–cement interface during the first few cycles of loading, even without a thin film. The results indicate that flanges have a greater effect on fixation than surface finish, and therefore adverse findings about matte surfaces should not necessarily apply to all double-tapered stems. Specifically, dorsal flanges enhance the stability of a tapered cemented femoral stem, regardless of surface finish. 相似文献
230.
Annemarieke de Jonghe Barbara C. van Munster J. Carel Goslings Peter Kloen Carolien van Rees Reinder Wolvius Romuald van Velde Marcel Levi Rob J. de Haan Sophia E. de Rooij 《CMAJ》2014,186(14):E547-E556