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31.
Volkmann N Hanein D Ouyang G Trybus KM DeRosier DJ Lowey S 《Nature structural biology》2000,7(12):1147-1155
Structural insights into the interaction of smooth muscle myosin with actin have been provided by computer-based fitting of crystal structures into three-dimensional reconstructions obtained by electron cryomicroscopy, and by mapping of structural and dynamic changes in the actomyosin complex. The actomyosin structures determined in the presence and absence of MgADP differ significantly from each other, and from all crystallographic structures of unbound myosin. Coupled to a complex movement ( approximately 34 A) of the light chain binding domain upon MgADP release, we observed a approximately 9 degrees rotation of the myosin motor domain relative to the actin filament, and a closure of the cleft that divides the actin binding region of the myosin head. Cleft closure is achieved by a movement of the upper 50 kDa region, while parts of the lower 50 kDa region are stabilized through strong interactions with actin. This model supports a mechanism in which binding of MgATP at the active site opens the cleft and disrupts the interface, thereby releasing myosin from actin. 相似文献
32.
To assess soil quality, a minimum dataset (MDS) of soil properties has to be proposed commonly through calculating the total load of each candidate soil parameter on all of the qualified principal components by use of principal component analysis (PCA) and Norm-value computation. Considering intensive land-use changes, the method introduced in this study on MDS establishment integrates the quantified contributions of land-use type and land-use duration on each soil parameter by using multivariate analysis and mean multiple comparison. In this way, a MDS maximally representing all candidates with minimal loss of the soil quality information contained by those non-MDS soil parameters is established. The MDS proposed can not only well integrate the quantified influence of land-use changes and land-use duration on soil parameters, but is also quite flexible and extendable with the potential to be extrapolated to assess soil quality in other regions. Based on two sets of soil database obtained separately in 1985 and 2004, two MDSs established are compared with each other. It is found that only quite a small change in MDS components occurs during a 20-year period. For a better assessment of soil quality, it seems necessary to examine on what kind of temporal scale and how much MDS will change for a site-specific area with intensive land-use changes. 相似文献
33.
Multichannel automated chamber system for continuous monitoring of CO2 exchange between the agro-ecosystem or soil and the atmosphere 总被引:1,自引:0,他引:1 下载免费PDF全文
A multichannel automated chamber system was developed for continuous monitoring of CO2 exchange at multiple points between agro-ecosystem or soil and atmosphere. This system consisted of an automated chamber subsystem with a CO2 concentration analyzer and a data logging subsystem. Both subsystems were under the control of a programmable logic controller (PLC). The automated chamber subsystem contained 18 chambers (50 cm × 50 cm × 50 cm) and a compressor. The chamber lids were closed and can be automatically opened. During measurement, one of the 18 chambers was kept closed for three minutes for measuring and the other chambers were kept open to maintain the natural soil conditions to the maximum extent. Environmental variables were simultaneously measured using sensors and recorded by the data logger. The reliability of the multichannel automated chamber system was tested and the results showed that the turbulence of the fans had no significant effect on the CO2 exchange. The changes in the air and the temperature of soil and soil moisture inside the chambers, caused by the enclosure of the chambers, were not significant. The net ecosystem CO2 exchange for the wheat ecosystem was ?2.35 μmol·m?2·s>?1 and the soil respiration was 3.87 μmol·m?2·s>?1 in the wheat field, and 6.61 μmol·m?2·s>?1 in the apple orchard. 相似文献
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36.
植物通过内源激素或环境信号调控叶腋内腋芽的形成和发育,从而控制其分枝特性。独脚金内酯(strigolactones,SLs),一种产生于植物根部的类胡萝卜素衍生物,具有刺激寄生植物种子的萌发和促进丛枝菌根真菌菌丝分枝的作用,最近的研究表明,它还可以沿茎干向上运输,与生长素和细胞分裂素一起直接或间接抑制植物分枝,目前已经作为一种新的植物激素受到广泛认可。本文综述了独脚金内酯的结构、合成途径和生物活性,以及调控植物分枝的分子机理,并展望了其在抑制杂草或新型除草剂的研发、促进植物和有益真菌的共生,以及调控作物的分枝和株型等方面的应用前景。 相似文献
37.
In this work, we examined the genetic diversity and evolution of the WAG-2 gene based on new WAG-2 alleles isolated from wheat and its relatives. Only single nucleotide polymorphisms (SNP) and no insertions and deletions (indels) were found in exon sequences of WAG-2 from different species. More SNPs and indels occurred in introns than in exons. For exons, exons+introns and introns, the nucleotide polymorphism π decreased from diploid and tetraploid genotypes to hexaploid genotypes. This finding indicated that the diversity of WAG-2 in diploids was greater than in hexaploids because of the strong selection pressure on the latter. All dn/ds ratios were < 1.0, indicating that WAG-2 belongs to a conserved gene affected by negative selection. Thirty-nine of the 57 particular SNPs and eight of the 10 indels were detected in diploid species. The degree of divergence in intron length among WAG-2 clones and phylogenetic tree topology suggested the existence of three homoeologs in the A, B or D genome of common wheat. Wheat AG-like genes were divided into WAG-1 and WAG-2 clades. The latter clade contained WAG-2, OsMADS3 and ZMM2 genes, indicating functional homoeology among them. 相似文献
38.
Yu S Ouyang A 《American journal of physiology. Gastrointestinal and liver physiology》2011,301(6):G1052-G1058
Eosinophilic esophagitis is characterized by increased infiltration and degranulation of eosinophils in the esophagus. Whether eosinophil-derived cationic proteins regulate esophageal sensory nerve function is still unknown. Using synthetic cationic protein to investigate such effect, we performed extracellular recordings from vagal nodose or jugular neurons in ex vivo esophageal-vagal preparations with intact nerve endings in the esophagus. Nerve excitabilities were determined by comparing action potentials evoked by esophageal distensions before and after perfusion of synthetic cationic protein poly-L-lysine (PLL) with or without pretreatment with poly-L-glutamic acid (PLGA), which neutralized cationic charges of PLL. Perfusion with PLL did not evoke action potentials in esophageal nodose C fibers but increased their responses to esophageal distension. This potentiation effect lasted for 30 min after washing out of PLL. Pretreatment with PLGA significantly inhibited PLL-induced mechanohyperexcitability of esophageal nodose C fibers. In esophageal nodose Aδ fibers, perfusion with PLL did not evoke action potentials. In contrast to nodose C fibers, both the spontaneous discharges and the responses to esophageal distension in nodose Aδ fibers were decreased by perfusion with PLL, which can be restored after washing out PLL for 30-60 min. Pretreatment with PLGA attenuated PLL-induced decrease in spontaneous discharge and mechanoexcitability of esophageal nodose Aδ fibers. In esophageal jugular C fibers, PLL neither evoked action potentials nor changed their responses to esophageal distension. Collectively, these data demonstrated that synthetic cationic protein did not evoke action potential discharges of esophageal vagal afferents but had distinctive sensitization effects on their responses to esophageal distension. 相似文献
39.
Chanjuan Zhang Bo Ouyang Changxian Yang Xiaohui Zhang Hui Liu Yuyang Zhang Junhong Zhang Hanxia Li Zhibiao Ye 《PloS one》2013,8(4)
As a vital antioxidant, L-ascorbic acid (AsA) affects diverse biological processes in higher plants. Lack of AsA in cell impairs plant development. In the present study, we manipulated a gene of GDP-mannose pyrophosphorylase which catalyzes the conversion of D-mannose-1-P to GDP-D-mannose in AsA biosynthetic pathway and found out the phenotype alteration of tomato. In the tomato genome, there are four members of GMP gene family and they constitutively expressed in various tissues in distinct expression patterns. As expected, over-expression of SlGMP3 increased total AsA contents and enhanced the tolerance to oxidative stress in tomato. On the contrary, knock-down of SlGMP3 significantly decreased AsA contents below the threshold level and altered the phenotype of tomato plants with lesions and further senescence. Further analysis indicated the causes for this symptom could result from failing to instantly deplete the reactive oxygen species (ROS) as decline of free radical scavenging activity. More ROS accumulated in the leaves and then triggered expressions of defence-related genes and mimic symptom occurred on the leaves similar to hypersensitive responses against pathogens. Consequently, the photosynthesis of leaves was dramatically fallen. These results suggested the vital roles of AsA as an antioxidant in leaf function and defence response of tomato. 相似文献
40.
Metal ion binding to calmodulin: NMR and fluorescence studies 总被引:13,自引:0,他引:13
Calmodulin is an important second messenger protein which is involved in a large variety of cellular path-ways.Calmodulin is sensitive to fluctuations in the intracellular Ca levels and is activated by the bindingof four Ca ions. In spite of the important role it plays in signal transduction pathways, it shows a surpris-inglybroad specificity for binding metal ions. Using 15N-Gly biosynthetically-labelled calmodulin, we havestudied the binding of different metal ions to calmodulin, including K+, Na+, Ca, Mg, Zn, Cd, Pb, Hg, Sr, La and Lu, by 1H, 15N HMQC NMR experiments. The effects of these ions on the substrate-bindingability of calmodulin have also been studied by fluorescence spectroscopy of the single tryptophan residue in a 22-residue synthetic peptide encompassing the skeletal muscle myosin light chain kinase calmod-ulin-binding domain. Most of these metal ions can activate a calmodulin target enzyme to some extent,though they bind to calmodulin in a different manner. Mg, which is of direct physiological interest, has adistinct site-preference for calmodulin, as it shows the highest affinity for site I in the N-terminal domain,while the C-terminal sites III and IV are the high affinity binding sites for Ca (as well as for Cd ). At ahigh concentration of Mg and a low concentration of Ca, calmodulin can bind Mg in its N-terminallobe while the C-terminal domain is occupied by Ca; this species could exist in resting cells in which the Mg level significantly exceeds that of Ca. Moreover, our data suggest that the toxicity of Pb-which,like Sr, binds with an equal and high affinity to all four sites-may be related to its capacity to tightlybind and improperly activate calmodulin. 相似文献