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91.
Dimer-tetramer transition between solution and crystalline states of streptavidin and avidin mutants 下载免费PDF全文
Pazy Y Eisenberg-Domovich Y Laitinen OH Kulomaa MS Bayer EA Wilchek M Livnah O 《Journal of bacteriology》2003,185(14):4050-4056
The biotin-binding tetrameric proteins, streptavidin from Streptomyces avidinii and chicken egg white avidin, are excellent models for the study of subunit-subunit interactions of a multimeric protein. Efforts are thus being made to prepare mutated forms of streptavidin and avidin, which would form monomers or dimers, in order to examine their effect on quaternary structure and assembly. In the present communication, we compared the crystal structures of binding site W-->K mutations in streptavidin and avidin. In solution, both mutant proteins are known to form dimers, but upon crystallization, both formed tetramers with the same parameters as the native proteins. All of the intersubunit bonds were conserved, except for the hydrophobic interaction between biotin and the tryptophan that was replaced by lysine. In the crystal structure, the binding site of the mutated apo-avidin contains 3 molecules of structured water instead of the 5 contained in the native protein. The lysine side chain extends in a direction opposite that of the native tryptophan, the void being partially filled by an adjacent lysine residue. Nevertheless, the binding-site conformation observed for the mutant tetramer is an artificial consequence of crystal packing that would not be maintained in the solution-phase dimer. It appears that the dimer-tetramer transition may be concentration dependent, and the interaction among subunits obeys the law of mass action. 相似文献
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93.
Marcus Clauss Julia Fritz Dorothee Bayer Jürgen Hummel W. Jürgen Streich Karl-Heinz Südekum Jean-Michel Hatt 《Zoology (Jena, Germany)》2009,112(3):195-205
In domestic ruminants, the stratification of forestomach contents – the results of flotation and sedimentation processes – is an important prerequisite for the selective particle retention in this organ. A series of anatomical and physiological measurements suggests that the degree of this stratification varies between browsing and grazing wild ruminants. We investigated the forestomach contents of free-ranging mouflon and roe deer shot during regular hunting procedures. There was no difference between the species in the degree by which forestomach ingesta separated according to size due to buoyancy characteristics in vitro. However, forestomach fluid of roe deer was more viscous than that of mouflon, and no difference in moisture content was evident between the dorsal and the ventral rumen in roe deer, in contrast to mouflon. Hence, the forestomach milieu in roe deer appears less favourable for gas or particle separation due to buoyancy characteristics. These findings are in accord with notable differences in forestomach papillation between the two species. In roe deer, particle separation is most likely restricted to the reticulum, whereas in mouflon, the whole rumen may pre-sort particles to a higher degree. The results suggest that differences in forestomach physiology may occur across ruminant species. 相似文献
94.
Sergey G. Ermilov Dorothee Sandmann Bernhard Klarner Rahaju Widyastuti Stefan Scheu 《ZooKeys》2015,(539):11-51
Seven new species of oribatid mites of the genus Galumna are described from litter and soil materials of Sumatra, Indonesia. A new subgenus, Galumna (Atypicogalumna)
subgen. n., is proposed; it differs from all galumnid genera and subgenera by the simultaneous presence of porose areas and sacculi on the notogaster (vs. either porose areas or sacculi present). Galumna (Galumna) calva Starý, 1997 is recorded for the first time in the Oriental region, and Galumna (Galumna) sabahna Mahunka, 1995 is recorded for the first time in the Indonesian fauna. 相似文献
95.
Daniel J. Barnett Ran D. Balicer Carol B. Thompson J. Douglas Storey Saad B. Omer Natalie L. Semon Steve Bayer Lorraine V. Cheek Kerry W. Gateley Kathryn M. Lanza Jane A. Norbin Catherine C. Slemp Jonathan M. Links 《PloS one》2009,4(7)
Background
Local public health agencies play a central role in response to an influenza pandemic, and understanding the willingness of their employees to report to work is therefore a critically relevant concern for pandemic influenza planning efforts. Witte''s Extended Parallel Process Model (EPPM) has been found useful for understanding adaptive behavior in the face of unknown risk, and thus offers a framework for examining scenario-specific willingness to respond among local public health workers. We thus aim to use the EPPM as a lens for examining the influences of perceived threat and efficacy on local public health workers'' response willingness to pandemic influenza.Methodology/Principal Findings
We administered an online, EPPM-based survey about attitudes/beliefs toward emergency response (Johns Hopkins∼Public Health Infrastructure Response Survey Tool), to local public health employees in three states between November 2006 – December 2007. A total of 1835 responses were collected for an overall response rate of 83%. With some regional variation, overall 16% of the workers in 2006-7 were not willing to “respond to a pandemic flu emergency regardless of its severity”. Local health department employees with a perception of high threat and high efficacy – i.e., those fitting a ‘concerned and confident’ profile in the EPPM analysis – had the highest declared rates of willingness to respond to an influenza pandemic if required by their agency, which was 31.7 times higher than those fitting a ‘low threat/low efficacy’ EPPM profile.Conclusions/Significance
In the context of pandemic influenza planning, the EPPM provides a useful framework to inform nuanced understanding of baseline levels of – and gaps in – local public health workers'' response willingness. Within local health departments, ‘concerned and confident’ employees are most likely to be willing to respond. This finding may allow public health agencies to design, implement, and evaluate training programs focused on emergency response attitudes in health departments. 相似文献96.
Jonathan Caspi Diana Irwin Raphael Lamed Yuval Shoham Henri-Pierre Fierobe David B. Wilson Edward A. Bayer 《Biocatalysis and Biotransformation》2006,24(1):3-12
During the course of our studies on the structure-function relationship of cellulosomes, we were interested in converting the free cellulase system of the aerobic bacterium, Thermobifida fusca, to a cellulosomal system. For this purpose, the cellulose-binding modules (CBM) of two T. fusca family-6 cellulases, endoglucanase Cel6A and exoglucanase Cel6B, were replaced by divergent dockerin modules. Thus far, family-6 cellulases have not been shown to be members of natural cellulosome systems. The resultant chimaeric proteins, 6A-c and t-6B, respectively, were purified and found to interact specifically and stoichiometrically with their corresponding cohesin modules, indicating their suitability for use as components in 'designer cellulosomes'. Both chimaeric enzymes showed somewhat decreased but measurable levels of activity on carboxymethyl cellulose, consistent with the known endo- and exo-glucanase character of the parent enzymes. The activity of 6A-c on phosphoric acid swollen cellulose was also consistent with that of the wild-type endoglucanase Cel6A. The startling finding of the present research was the extent of degradation of this substrate by the chimaeric enzyme t-6B. Wild-type exoglucanase Cel6B exhibited very low activity on this substrate, while the specific activity of t-6B was 14-fold higher than the parent enzyme. 相似文献
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98.
Amino Acids - It is known for almost 25 years that the corpora cardiaca (neurosecretory glands) of cicadas synthesize two isobaric peptides with hypertrehalosaemic activity denominated... 相似文献
99.
The Gnaphalieae are a group of sunflowers that have their greatest diversity in South America, Southern Africa, and Australia. The objective of this study was to reconstruct a phylogeny of the South African Gnaphalieae using sequence data from two noncoding chloroplast DNA sequences, the trnL intron and trnL/trnF intergenic spacer. Included in this investigation are the genera of the Gnaphalieae from the African basal groups, members of the subtribes Cassiniinae, Gnaphaliinae, and Relhaniinae, and African representatives from the large Old World genus Helichrysum. Results indicate that two Gnaphaloid genera, Printzia and Callilepis, should be excluded from the Gnaphalieae. In most trees the Relhaniinae s.s. (sensu stricto) and some of the basal taxa comprise a clade that is sister to the remainder of the tribe Gnaphalieae. The Relhaniinae, which are restricted to Africa, are not a monophyletic group as presently circumscribed, nor are the South African members of Helichrysum, the Cassiniinae and Gnaphaliinae. There is general agreement between our molecular analysis and that of morphology, particularly in the terminal branches of the trees. 相似文献
100.
Tetrazolium salts like 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) or sodium 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) that form formazans after reduction are widely used to investigate cell viability. Besides cellular enzymes, some constituents of cell media and other substances reduce tetrazolium salts, thereby interfering with these assays. We describe here that different preparations of serum albumin from bovine or human origin can lead to a concentration-dependent increase in the signals of the XTT assay; therefore leading to an overestimation of cell numbers and to an underestimation of potential cytotoxic effects of compounds to be tested. The same effect was seen in the MTT assay with human serum albumin (HSA). We demonstrate that this reductive activity cannot be inactivated by proteolytic digestion, but that it is due to the free cysteine residue in albumin, and is also observed when cysteine or glutathione (GSH) are used. Binding of N-ethylmaleimide (NEM) to the free cysteine residue leads to a decrease of the albumin interference in the XTT assay. 相似文献