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Receptor binding studies were performed with 125I-labeled trypsin-activated insecticidal toxins, CryIA(a) and CryIA(c), from Bacillus thuringiensis on brush-border membrane vesicles (BBMV) prepared from Bombyx mori larval midgut. Bioassays were performed by gently force feeding B. mori with diluted toxins. CryIA(a) toxin (LD50; 0.002 micrograms) was 200 times more active against B. mori larvae than CryIA(c) toxin (LD50; 0.421 micrograms) and showed high-affinity saturable binding. The Kd and the binding site concentration for CryIA(a) toxin were 3.5 nM and 7.95 pmol/mg, respectively. CryIA(c) toxin (Kd, 50.35 nM; Bmax, 2.85 pmol/mg) did not demonstrate high-affinity binding to B. mori BBMV. Control experiments with CryIA(a) and CryIA(c) toxins revealed no binding to mouse small intestine BBMV and nonspecific binding to pig kidney BBMV. These data provide evidence that binding to a specific receptor on the membrane of midgut epithelial cells is an important determinant with respect to differences in insecticidal spectrum of insecticidal crystal proteins. To locate a B. mori receptor binding region on the CryIA(a) toxin, homologous and heterologous competition binding studies were performed with a set of mutant proteins which had previously been used to define the B. mori "specificity domain" on this toxin (Ge, A. Z., Shivarova, N. I., and Dean, D. H. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 4037-4041). These mutant proteins have had regions of their genes reciprocally exchanged with the cryIA(c) gene. A B. mori receptor binding region on CryIA(a) toxin includes the amino-terminal portion of the hypervariable region, amino acids 332-450, which is identical to the previously described B. mori specificity determining region. These data provide direct evidence that delta-endotoxins contain a tract of amino acids that comprise a binding region and as a results determines the specificity of a toxin.  相似文献   
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R W Milne  Y L Marcel 《FEBS letters》1982,146(1):97-100
Because of its physical properties, apolipoprotein B (apo B) has remained poorly characterized. In an attempt to elucidate apo B structure, the Fab fragments of 3 different monoclonal anti-human apo B antibodies were tested in a quantitative assay for their binding to human low density lipoprotein (LDL). In each case the assay gave a linear Scatchard plot with a maximum of 1 Fab fragment bound to a single LDL particle. This result favors an LDL model containing a single large Mr apo B protein, which is not composed of multiple, identical, small Mr subunits.  相似文献   
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Heat-labile antigens of Salmonella enteritidis. I. Extraction of antigens   总被引:3,自引:0,他引:3  
Milne, Margaret (University of Adelaide, Adelaide, Australia), and F. M. Collins. Heat-labile antigens of Salmonella enteritidis. I. Extraction of antigens. J. Bacteriol. 92:543-548. 1966.-Salmonella enteritidis strains of high and low mouse virulence were grown in continuous culture. Cell walls were obtained from both strains by sonic disruption, and the washed walls were extracted at 4 C with sodium dodecyl sulfate or sodium deoxycholate. The extracts were eluted with a saline gradient from a diethylaminoethyl cellulose column, and the separated peaks were tested for precipitin activity against rabbit antisera prepared with heator ethyl alcohol-killed vaccines. The separated antigens reacted less intensely with the antiserum to heat-killed cells than they did to the antisera prepared against alcohol-killed vaccine. Little antigenic difference could be detected between the extracts prepared from the virulent and the avirulent organisms.  相似文献   
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Previous modelling of single channel behaviour based on Markov processes has been concerned mainly with means and marginal distributions of particular quantities. The present study derives the joint distribution, conditional distributions, and associated mean values for the burst length (T) and the number (N) of openings per burst in two simple three-state models in which bursting is possible, one for an agonist-only and one for a channel blocking mechanism. In both models the conditional mean burst length (E(T/N = r)) increases linearly as a function of the number of openings per burst, while the conditional mean number of openings per burst (E(N/T = x)) is a nonlinear strictly increasing function of burst length, which is asymptotically linear for large burst length. The asymptotic intercept for each model is shown to be less than, equal to, or greater than unity according as mean channel closed-time is less than, equal to, or greater than mean open-time. For parameter values typical of the nicotinic receptor, this intercept is less than unity for the agonist-only model and greater than unity for the blocking model. As a result of the dependence between the number of openings per burst and burst length, it is shown that experimental estimates of the unconditional mean number of openings per burst may be biased if bursts of only short duration are collected.  相似文献   
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Continental margins are disproportionally important for global primary production, fisheries and CO2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biota—large diatoms, dinoflagellates and copepods—that traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these declines to summer nutrient stress and increasing proportions of picophytoplankton that can comprise up to 90% of the combined pico‐ and nanophytoplankton biomass in coastal areas. Among the pico‐fraction, it is the cyanobacterium Synechococcus that flourishes when iron and nitrogen resupply to surface waters are diminished. Our field data show how traits beyond small size give Synechococcus a competitive edge over pico‐ and nanoeukaryotes. Key is their ability to grow at low irradiances near the nutricline, which is aided by their superior light‐harvesting system and high affinity to iron. However, minute size and lack of essential biomolecules (e.g. omega‐3 polyunsaturated fatty acids and sterols) render Synechococcus poor primary producers to sustain shelf sea food webs efficiently. The combination of earlier spring blooms and lower summer food quantity and quality creates an increasing period of suboptimal feeding conditions for zooplankton at a time of year when their metabolic demand is highest. We suggest that this nutrition‐related mismatch has contributed to the widespread, ~50% decline in summer copepod abundance we observe over the last 60 years. With Synechococcus clades being prominent from the tropics to the Arctic and their abundances increasing worldwide, our study informs projections of future food web dynamics in coastal and shelf areas where droughts and stratification lead to increasing nutrient starvation of surface waters.  相似文献   
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Having a comprehensive understanding of population structure, genetic differentiation and demographic history is important for the conservation and management of threatened species. High‐throughput sequencing (HTS) provides exciting opportunities to address a wide range of factors for conservation genetics. Here, we generated HTS data and identified 266,884 high‐quality single nucleotide polymorphisms from 82 individuals of Cupressus chengiana, to assess population genomics across the species' full range, comprising the Daduhe River (DDH), Minjiang River (MJR) and Bailongjiang River (BLJ) catchments in western China. admixture , principal components analysis and phylogenetic analyses indicated that each region contains a distinct lineage, with high levels of differentiation between them (DDH, MJR and BLJ lineages). MJR was newly distinguished compared to previous surveys, and evidence including coalescent simulations supported a hybrid origin of MJR during the Quaternary. Each of these three lineages should be recognized as an evolutionarily significant unit (ESU), due to isolation, differing genetic adaptations and different demographic history. Currently, each ESU faces distinct threats, and will require different conservation strategies. Our work shows that population genomic approaches using HTS can reconstruct the complex evolutionary history of threatened species in mountainous regions, and hence inform conservation efforts, and contribute to the understanding of high biodiversity in mountains.  相似文献   
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