共查询到20条相似文献,搜索用时 8 毫秒
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S. A. Nadler 《Journal of nematology》1996,28(3):277-285
Molecular markers have been used only rarely to characterize the population genetic structure of nematodes. Published studies have suggested that different taxa may show distinct genetic architectures. Isoenzyme and RAPD markers have been used to investigate geographic variation of Ascaris suum at the level of infrapopulations (nematodes within individual hosts), within localities, and among geographic regions. Independent estimates of genetic differentiation among population samples based on isoenzyme and RAPD data showed similar patterns and substantial correlation. Heterozygote deficiencies within infrapopulations and large values for inbreeding coefficients among infrapopulations suggested that the composition of these populations was not consistent with a model of random recruitment from a large panmictic pool of life-cycle stages. Both isoenzyme and RAPD markers revealed moderate levels of genetic differentiation among samples representing infrapopulations and localities. Of total gene diversity, 9.4% (isoenzyme) and 9.2% (RAPD) was partitioned among infrapopulations. Geographic localities accounted for 7.8% (isoenzyme) and 6.2% (RAPD) of total diversity. Only infrapopulations from the same farm had low levels of differentiation. 相似文献
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Joseph F. Urban Jr Yan Hu Melanie M. Miller Ulrike Scheib Ying Y. Yiu Raffi V. Aroian 《PLoS neglected tropical diseases》2013,7(6)
Ascaris suum and Ascaris lumbricoides are two closely related geo-helminth parasites that ubiquitously infect pigs and humans, respectively. Ascaris suum infection in pigs is considered a good model for A. lumbricoides infection in humans because of a similar biology and tissue migration to the intestines. Ascaris lumbricoides infections in children are associated with malnutrition, growth and cognitive stunting, immune defects, and, in extreme cases, life-threatening blockage of the digestive tract and aberrant migration into the bile duct and peritoneum. Similar effects can be seen with A. suum infections in pigs related to poor feed efficiency and performance. New strategies to control Ascaris infections are needed largely due to reduced treatment efficacies of current anthelmintics in the field, the threat of resistance development, and the general lack of new drug development for intestinal soil-transmitted helminths for humans and animals. Here we demonstrate for the first time that A. suum expresses the receptors for Bacillus thuringiensis crystal protein and novel anthelmintic Cry5B, which has been previously shown to intoxicate hookworms and which belongs to a class of proteins considered non-toxic to vertebrates. Cry5B is able to intoxicate A. suum larvae and adults and triggers the activation of the p38 mitogen-activated protein kinase pathway similar to that observed with other nematodes. Most importantly, two moderate doses of 20 mg/kg body weight (143 nM/kg) of Cry5B resulted in a near complete cure of intestinal A. suum infections in pigs. Taken together, these results demonstrate the excellent potential of Cry5B to treat Ascaris infections in pigs and in humans and for Cry5B to work effectively in the human gastrointestinal tract. 相似文献
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Patricia Ponce de León Gonzalo Del Balzo Bibiana Riquelme 《Cell biochemistry and biophysics》2013,65(2):237-242
Previous studies have shown that A. lumbricoides extracts capture sialic acid (SA) from human red blood cells (RBC). The aim of this work was to study hemorheological alterations in vitro caused by parasite larvae. The biorheological action of three larva concentrates of first and second larval stage on group O erythrocytes was analyzed by incubating the erythrocyte packed together with an equal volume of larvae (treated RBC) and PBS (control RBC). Distribution and parameters of aggregation (digital image analysis), aggregation kinetics (erythroaggregameter), and viscoelasticity (erythrodeformeter) were measured. The digital image analysis showed that all the larvae diminished the isolated cells percentage and increased the size of the formed aggregates. The aggregate formation velocity was lower in the treated than in the control. The deformability index (ID) values of treated RBC did not present variations with respect to those of the control, but a decrease in the erythrocyte elastic modulus (μm) and membrane surface viscosity (ηm) values was observed, indicating that the larvae not only induced a diminution in the membrane surface viscosity of RBC but also altered the dynamic viscoelasticity of the membrane. Experiments carried out in vitro support the conclusion that the contact between larvae and RBC produces hemorheological alterations. 相似文献
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D Fujimoto 《Journal of biochemistry》1975,78(5):905-909
The collagen from the cuticle of Ascaris lumbricoides was digested by Clostridium histolyticum collagenase [EC 3.4.24.3] in the presence and absence of CaCl2. About 1.2 mumoles of amino groups per mg collagen was liberated when the digestion was performed in the presence of 5 mM CaCl2, whereas about 0.5 mumole of amino groups per mg collagen was liberated by digestion in the absence of CaCl2. In contrast, CaCl2 influenced the extent of hydrolysis of rat tail tendon collagen only slightly. The results suggest that CaCl2 is necessary for the hydrolysis of certain regions in the molecule of Ascaris collagen and that such structures may not be present in mammalian collagens. 相似文献
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Melanie Abongwa Katherine E. Baber Richard J. Martin Alan P. Robertson 《Invertebrate neuroscience : IN》2016,16(4):10
Nematode parasite infections pose a significant threat in human and veterinary medicine. At least a third of the world’s population is at risk from nematode parasite infections. These infections not only cause health problems, but also cause loss of livestock production and hence, economic losses. Anthelmintic drugs are the mainstay by which control of nematode parasite infections is achieved. Many of the currently available anthelmintics act on nicotinic acetylcholine receptors (nAChRs). However, the detailed mode of action (MOA) of these anthelmintics is not clearly understood. Elucidation of the MOA of anthelmintics is highly desirable; an in-depth knowledge of the MOA will better inform on mechanisms of resistance development and on ways to slow down or overcome resistance. The cholinomimetic anthelmintic, morantel, has a complex MOA involving the activation and block of levamisole-sensitive single nAChR channels (L-type nAChR or L-nAChR). More recently, morantel has been demonstrated to activate Haemonchus contortus and Parascaris equorum ACR-26/ACR-27 nAChRs expressed in Xenopus laevis oocytes. Previous studies in our laboratory, however, have shown morantel does not activate the nicotine-sensitive nAChR (N-type nAChR or N-nAChR), Ascaris suum ACR-16 (Asu-ACR-16). In this study, we used two-electrode voltage-clamp (TEVC) electrophysiology to investigate the inhibitory effects of morantel, on expressed Asu-ACR-16 nAChRs in X. laevis oocytes. Our results show that morantel acts as a non-competitive antagonist on Asu-ACR-16. This non-competitive antagonism by morantel was further demonstrated to be voltage-sensitive. We conclude based on our findings that morantel is a non-competitive voltage-sensitive open channel blocker of Asu-ACR-16. 相似文献
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Vladimir Avdonin Erwin F. Shibata Toshinori Hoshi 《The Journal of general physiology》1997,109(2):169-180
Dihydropyridines (DHPs) are well known for their effects on L-type voltage-dependent Ca2+ channels. However, these drugs also affect other voltage-dependent ion channels, including Shaker K+ channels. We examined the effects of DHPs on the Shaker K+ channels expressed in Xenopus oocytes. Intracellular applications of
DHPs quickly and reversibly induced apparent inactivation in the Shaker K+ mutant channels with disrupted
N- and C-type inactivation. We found that DHPs interact with the open state of the channel as evidenced by the
decreased mean open time. The DHPs effects are voltage-dependent, becoming more effective with hyperpolarization. A model which involves binding of two DHP molecules to the channel is consistent with the results obtained in our experiments. 相似文献
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Christina Gabrielsen Dag A. Brede Ingolf F. Nes Dzung B. Diep 《Applied and environmental microbiology》2014,80(22):6854-6862
Circular bacteriocins are a group of N-to-C-terminally linked antimicrobial peptides, produced by Gram-positive bacteria of the phylum Firmicutes. Circular bacteriocins generally exhibit broad-spectrum antimicrobial activity, including against common food-borne pathogens, such as Clostridium and Listeria spp. These peptides are further known for their high pH and thermal stability, as well as for resistance to many proteolytic enzymes, properties which make this group of bacteriocins highly promising for potential industrial applications and their biosynthesis of particular interest as a possible model system for the synthesis of highly stable bioactive peptides. In this review, we summarize the current knowledge on this group of bacteriocins, with emphasis on the recent progress in understanding circular bacteriocin genetics, biosynthesis, and mode of action; in addition, we highlight the current challenges and future perspectives for the application of these peptides. 相似文献
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Sheila B. Ogoma Hassan Ngonyani Emmanuel T. Simfukwe Antony Mseka Jason Moore Marta F. Maia Sarah J. Moore Lena M. Lorenz 《PloS one》2014,9(12)
Malaria vector control relies on toxicity of insecticides used in long lasting insecticide treated nets and indoor residual spraying. This is despite evidence that sub–lethal insecticides reduce human–vector contact and malaria transmission. The impact of sub–lethal insecticides on host seeking and blood feeding of mosquitoes was measured. Taxis boxes distinguished between repellency and attraction inhibition of mosquitoes by measuring response of mosquitoes towards or away from Transfluthrin coils and humans. Protective effective distance of coils and long-term effects on blood feeding were measured in the semi–field tunnel and in a Peet Grady chamber. Laboratory reared pyrethroid susceptible Anopheles gambiae sensu stricto mosquitoes were used. In the taxis boxes, a higher proportion of mosquitoes (67%–82%) were activated and flew towards the human in the presence of Transfluthrin coils. Coils did not hinder attraction of mosquitoes to the human. In the semi–field Tunnel, coils placed 0.3 m from the human reduced feeding by 86% (95% CI [0.66; 0.95]) when used as a “bubble” compared to 65% (95% CI [0.51; 0.76]) when used as a “point source”. Mosquitoes exposed to coils inside a Peet Grady chamber were delayed from feeding normally for 12 hours but there was no effect on free flying and caged mosquitoes exposed in the semi–field tunnel. These findings indicate that airborne pyrethroids minimize human–vector contact through reduced and delayed blood feeding. This information is useful for the development of target product profiles of spatial repellent products that can be used to complement mainstream malaria vector control tools. 相似文献
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Ellison M Haberlandt C Gomez-Casati ME Watkins M Elgoyhen AB McIntosh JM Olivera BM 《Biochemistry》2006,45(5):1511-1517
The alpha9 and alpha10 nicotinic acetylcholine receptor (nAChR) subunits assemble to form the alpha9alpha10 nAChR subtype. This receptor is believed to mediate cholinergic synaptic transmission between efferent olivocochlear fibers and the hair cells of the cochlea. In addition alpha9 and/or alpha10 expression has been described in dorsal root ganglion neurons, lymphocytes, skin keratinocytes, and the pars tuberalis of the pituitary. Specific antagonists that selectively block the alpha9alpha10 channel could be valuable tools for elucidating its role in these diverse tissues. This study describes a novel alpha-conotoxin from the Western Atlantic species Conus regius, alpha-conotoxin RgIA (alpha-RgIA), that is a subtype specific blocker of the alpha9alpha10 nAChR. alpha-RgIA belongs to the alpha4/3 subfamily of the alpha-conotoxin family; sequence and subtype specificity comparisons between alpha-RgIA and previously characterized alpha4/3 toxins indicate that the amino acids in the C-terminal half of alpha-RgIA are responsible for its preferential inhibition of the alpha9alpha10 nAChR subtype. 相似文献
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The prevalence of human and animal helminth infections remains staggeringly high, thus urging the need for concerted efforts towards this area of research. GABA receptors, encoded by the unc-49 gene, mediate body muscle inhibition in Caenorhabditis elegans and parasitic nematodes and are targets of anthelmintic drugs. Thus, the characterization of nematode GABA receptors provides a foundation for rational anti-parasitic drug design. We therefore explored UNC-49 channels from C. elegans muscle cultured cells of the first larval stage at the electrophysiological and behavioral levels. Whole-cell recordings reveal that GABA, muscimol and the anthelmintic piperazine elicit macroscopic currents from UNC-49 receptors that decay in their sustained presence, indicating full desensitization. Single-channel recordings show that all drugs elicit openings of ∼2.5 pA (+100 mV), which appear either as brief isolated events or in short bursts. The comparison of the lowest concentration required for detectable channel opening, the frequency of openings and the amplitude of macroscopic currents suggest that piperazine is the least efficacious of the three drugs. Macroscopic and single-channel GABA-activated currents are profoundly and apparently irreversibly inhibited by ivermectin. To gain further insight into ivermectin action at C. elegans muscle, we analyzed its effect on single-channel activity of the levamisol-sensitive nicotinic receptor (L-AChR), the excitatory receptor involved in neuromuscular transmission. Ivermectin produces a profound inhibition of the frequency of channel opening without significant changes in channel properties. By revealing that ivermectin inhibits C. elegans muscle GABA and L-AChR receptors, our study adds two receptors to the already known ivermectin targets, thus contributing to the elucidation of its pleiotropic effects. Behavioral assays in worms show that ivermectin potentiates piperazine-induced paralysis, thus suggesting that their combination is a good strategy to overcome the increasing resistance of parasites, an issue of global concern for human and animal health. 相似文献
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Grant E. Blouse Kenneth A. B?tkj?r Elena Deryugina Aleksandra A. Byszuk Janni M. Jensen Kim K. Mortensen James P. Quigley Peter A. Andreasen 《The Journal of biological chemistry》2009,284(7):4647-4657
Serine proteases are secreted from cells as single-chain zymogens,
typically having activities orders of magnitude lower than those of the mature
two-chain enzymes. Activation occurs by a conformational change initiated by
cleavage of a specific peptide bond. We have derived a monoclonal antibody
(mAb-112) which binds with subnanomolar affinity to pro-uPA, the zymogen form
of urokinase-type plasminogen activator (uPA). We mapped the epitope of the
antibody to the autolysis loop, one of the structural elements known to change
conformation during zymogen activation. A mechanistic evaluation with
biophysical methods elucidated a novel bifunctional inhibitory mechanism
whereby mAb-112 not only delays the proteolytic conversion of single-chain
pro-uPA into the two-chain form but also subsequently averts the
conformational transition to a mature protease by sequestering the two-chain
form in a zymogen-like, noncatalytic state. Functional studies employing two
variants of human HT-1080 cells, exhibiting high and low levels of
dissemination in a chorioallantoic membrane assay, demonstrate that mAb-112 is
an effective inhibitor of tumor cell intravasation. These findings show that
pharmacological interference with zymogen activation is a plausible and robust
means to regulate uPA activity and the downstream effects of plasminogen
activation in the spread of cancer and other processes of pathological tissue
remodeling. A strategy that targets regions related to pro-enzyme activation
likely provide a unique inhibitor-protease interaction surface and is, thus,
expected to enhance the chances of engineering high inhibitor specificity. Our
results provide new information about the structural flexibility underlying
the equilibrium between active and inactive forms of serine proteases.In nature a key mechanism for regulation of serine proteases with a
trypsin-like fold is the activation of secreted zymogens or proenzymes, which
typically have activities orders of magnitude lower than the mature enzymes.
Zymogen activation is the central step in natural protease cascade regulation,
allowing for rapid amplification of the activation signal. The catalytic
activity of a zymogen relative to the mature protease can generally be thought
of as a problem of equilibrium between active and inactive conformational
states of the protease domain. Zymogen activation generally occurs by cleavage
of the bond between amino acid residues 15 and
16.2 The liberated
amino terminus inserts into a hydrophobic binding cleft of the catalytic
domain forming, in addition to hydrophobic interactions, a salt bridge to the
side chain of Asp194 which stabilizes the substrate binding pocket
and oxyanion hole in a catalytically productive conformation. Conformational
changes after cleavage involves four disordered regions of the activation
domain, including the activation loop (residues 16-21), the autolysis loop
(residues 142-152), the oxyanion stabilizing loop (residues 184-194), and the
S1 entrance frame (residues 216-223) (Fig.
1A) (for reviews, see Refs.
1-3).Open in a separate windowFIGURE 1.Three-dimensional structure of uPA. A, overview of the
three-dimensional structure of the serine protease domain of active uPA,
displayed as ribbons. Depicted as sticks are the residues
Ile16, Asp194, and Ser195. The activation
domain, i.e. the activation loop (residues 16-21), the autolysis loop
(residues 142-152), the oxyanion stabilizing loop (residues 184-193), and the
S1 entrance frame (residues 216-223) are colored green. B, the
epitope of mAb-112, displayed on a surface presentation of the serine protease
domain of active uPA. Alanine substitution of residues depicted in
red resulted in a significant change in the affinity to mAb-112,
whereas alanine substitution of residues depicted in blue did not.
C, a close up view of the autolysis loop (residues Gly141
to Lys156) and residues implicated in the binding of mAb-112. All
figures were constructed with Pymol on the basis of the coordinates given in
the PDB entry 1C5W.Several proteases contribute to a variety of pathophysiological states,
thus stimulating considerable interest in the design of specific inhibitors
for pharmacological intervention. Nonetheless, classical development of small
molecule inhibitors of serine proteases has proved a daunting task, with only
limited success in engineering inhibitors with high affinity and specificity
for related proteases possessing conserved active site architecture and
P13 specificity
(4,
5). Thus far targeting zymogen
activation instead of the mature protease has been a greatly under-exploited
strategy in therapeutic regulation of protease activity. This approach
provides an opportunity to target more unique interaction surfaces, thereby
increasing inhibitor specificity, and ultimately offering novel inhibitory
mechanisms. In addition, a more efficient inhibition is expected by targeting
enzymes functioning high up in a catalytic cascade.A serine protease of particular relevance for pursuing therapeutic
intervention is urokinase-type plasminogen activator
(uPA),4 which
catalyzes the conversion of plasminogen to the active protease plasmin, which
in turn acts directly on the degradation of extracellular matrix proteins
(6). Abnormal expression of uPA
is implicated in tissue remodeling in several pathological conditions,
including rheumatoid arthritis, allergic vasculitis, and xeroderma
pigmentosum. In particular, uPA is central to the invasive capacity of
malignant tumors (6). As with
all trypsin-like proteases, uPA has a catalytic serine protease domain with
surface-exposed loops around residues 37, 60, 97, 110, 170, and 185. Besides
the catalytic domain, uPA has an amino-terminal extension consisting of a
kringle domain and an epidermal growth factor domain. The latter domain
functions in binding to the cell surface-anchored uPA receptor (uPAR)
(6). Several proteases
including plasmin (6),
glandular kallikrein (7),
matriptase (8), and hepsin
(9) can catalyze the activation
of the zymogen, pro-uPA.A number of inhibitors targeting the proteolytic activity of uPA have been
developed, such as small organochemical molecules, peptides, and monoclonal
antibodies, with a perspective on their use for elucidating the
pathophysiological functions of its various molecular interactions and
generating leads during drug development. The most specific inhibitors to date
appear to be those derived from antibodies and peptidyl inhibitors, which
utilize binding sites involving surface loops of uPA and extended exosite
interactions to drive selectivity and specificity (for reviews, see Refs.
4 and
5).Here we present evidence that targeting zymogen activation is an effective
means to regulate protease activity. This conclusion was realized through the
development and biochemical analysis of an inhibitory monoclonal antibody,
referred to as monoclonal antibody (mAb)-112, which not only delays cleavage
of pro-uPA but acts to stabilize the activated two-chain protease in a
non-catalytic conformation by restricting the conformational mobility of the
activation domain. Characterization of mAb-112 further provides new insights
into the flexibility of protease domains and uPA zymogen activation
mechanisms. Moreover, mAb-112 was shown to efficiently inhibit human tumor
cell intravasation, a step in the metastatic cascade in which activation of
pro-uPA was previously implicated as a key event
(10). 相似文献
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Lomofungin inhibited the growth of some yeasts and mycelial fungi at concentrations between 5 and 10 μg/ml. At such concentrations, there was no decrease in endogenous and exogenous oxygen consumption, and even 50 μg of antibiotic per ml caused only slight decreases. The permeation of the cell membrane was changed so that leakage of ninhydrin-positive substances was reduced, and the uptake of 14C-labeled glucose, amino acids, uracil, and thymidine was decreased at concentrations as low as 4 μg/ml. Protein synthesis in whole cells of Saccharomyces cerevisiae was reduced 35% at 10 μg/ml. However, the antibiotic did not reduce the incorporation of phenylalanine-U-14C into polypeptides with cell-free systems of Rhizoctonia solani and S. cerevisiae. The synthesis of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) was inhibited even at concentrations of lomofungin of 4 μg/ml. Since RNA synthesis was inhibited at lower concentrations and earlier than DNA synthesis, the primary site of action of the antibiotic appears to be the synthesis of RNA. 相似文献
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Chalongkwan Siddhikol John W. Erbstoeszer Bernard Weisblum 《Journal of bacteriology》1969,99(1):151-155
Streptolydigin and rifamycin inhibit the catalytic function of ribonucleic acid (RNA) polymerase. Streptolydigin can inhibit polymerization after the reaction has started, whereas rifamycin is effective only if it is preincubated with RNA polymerase prior to the addition of substrates. The same relationships are observed with respect to these two antibiotics if the nucleoside triphosphate-pyrophosphate exchange reaction is used in the assay system. The inhibitory effect of streptolydigin is reversible by further addition of RNA polymerase but not by addition of deoxyribonucleic acid to the assay system. 相似文献
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Bacillus cereus causes food poisoning and serious non-gastrointestinal-tract infections. Non-hemolytic enterotoxin (Nhe), which is present in most B. cereus strains, is considered to be one of the main virulence factors. However, a B. cereus ΔnheBC mutant strain lacking Nhe is still cytotoxic to intestinal epithelial cells. In a screen for additional cytotoxic factors using an in vitro model for polarized colon epithelial cells we identified B. cereus sphingomyelinase (SMase) as a strong inducer of epithelial cell death. Using single and double deletion mutants of sph, the gene encoding for SMase, and nheBC in B. cereus we demonstrated that SMase is an important factor for B. cereus cytotoxicity in vitro and pathogenicity in vivo. SMase substantially complemented Nhe induced cytotoxicity in vitro. In addition, SMase but not Nhe contributed significantly to the mortality rate of larvae in vivo in the insect model Galleria mellonella. Our study suggests that the role of B. cereus SMase as a secreted virulence factor for in vivo pathogenesis has been underestimated and that Nhe and SMase complement each other significantly to cause full B. cereus virulence hence disease formation. 相似文献