Three-dimensional structure determination of capsid of Aedes albopicus C6/36 cell densovirus

The three-dimensional structure of capsid of Aedes albopictus C6/36 densovirus was determined to 14-(A) resolution by electron cryomicroscopy and computer reconstruction. The triangulation number of the capsid is 1. There are 12 holes in each triangular face and a spike on each 5-fold vertex. The validity of the capsid and nucleic acid densities in the reconstructions was discussed.     

Three-dimensional structure determination of capsid of<Emphasis Type="Italic">Aedes albopictus</Emphasis> C6/36 cell densovirus

The three-dimensional structure of capsid ofAedes albopictus C6/36 densovirus was determined to 14-Å resolution by electron cryomicroscopy and computer reconstruction. The triangulation number of the capsid is 1. There are 12 holes in each triangular face and a spike on each 5-fold vertex. The validity of the capsid and nucleic acid densities in the reconstructions was discussed.     

胡椒碱对白纹伊蚊C6/36细胞株的毒性作用

采用MTT检测法、Annexin-V/PI双染流式细胞仪检测法及细胞形态学观察法,研究了植物型杀虫剂胡椒碱对白纹伊蚊Aedes albopictus C6/36细胞株的细胞毒性、诱导细胞凋亡与坏死的关系、Fas蛋白的表达、细胞生长状态改变及受损细胞的恢复。结果表明：胡椒碱浓度在0.035 mmol/L以上时可以诱发C6/36细胞形态学改变,在倒置显微镜下表现为细胞呈多形性,细胞胀大或皱缩,细胞间隙增宽,大片细胞聚集成团,脱落、崩解、死亡。用胡椒碱处理24 h后,对C6/36细胞的半数毒性浓度（IC₅₀）为 0.32 mmol/L,且毒性作用强度随着药物浓度增加而增强。Annexin-V/PI双染法检测结果显示药物浓度在0.28 mmol/L 以上诱导的细胞凋亡明显,药物浓度为0.56 mmol/L 时细胞凋亡率达19.4%,而药物引起的细胞总死亡率为72.7%;Fas蛋白表达在药物浓度0.28 mmol/L 以上时有所上调,但不明显。高浓度胡椒碱（0.56 mmol/L）分别作用于C6/36细胞24和48 h,在经历一段生长停滞后,24 h组受损细胞均可缓慢恢复,而48 h组细胞则出现不可逆性的损伤。由此认为：胡椒碱对C6/36细胞株有毒性作用,但药物诱导的细胞凋亡在细胞毒性作用机制中不占主导地位;胡椒碱对C6/36细胞的作用有时间依赖性,延长作用时间,药物对细胞的毒性作用增强。     

3D reconstruction and capsid protein characterization of grass carp reovirus

Grass carp reovirus (GCRV) is a relatively new virus first isolated in China and is a member of the Aquareovirus genus of the Reoviridae family. Recent report of genomic sequencing showed that GCRV shared high degree of homology with mammalian reovirus (MRV). As a step of our effort to understand the structural basis of GCRV pathogenesis, we determined the three-dimensional (3D) structure of GCRV capsid at 17 Å resolution by electron cryomicroscopy. Each GCRV capsid has a multilayered organization, consisting of an RNAcore, an inner, middle and outer protein layer. The outer layer is made up of 200 trimers that are arranged on an incomplete T=13 icosahedral lattice. A characteristic feature of this layer is the depression resulting from the absence of trimers around the peripentonal positions, revealing the underlying trimers on the middle layer. There are 120 subunits in the inner layer arranged with T=1 symmetry. These structural features are common to other members of the Reoviridae. Moreover, SDS-PAGE analysis showed that GCRV virions contain seven structural proteins (VP1-VP7). These structural proteins have a high degree of sequence homology to MRV, consistent with the structural similarities observed in our study. The high structural similarities of isolated GCRV and MRV suggest that future structural studies focusing on GCRV entering into and replicating within its host cell are necessary in order to fully understand the structural basis of GCRV pathogenesis.     

3D reconstruction and capsid protein characterization of grass carp reovirus

Grass carp reovirus (GCRV) is the first aquatic vi-rus isolated and characterized in mainland China[1]. In 1983, it was reported that GCRV was the agent that caused severe outbreaks of infectious hemorrhage disease in grass carp (Cyenopharyngodon idellus). Subsequently, a series of relatively systematic analyses have been conducted to characterize the biological and molecular properties of GCRV[2-8]. More than 50 aquareoviruses have been identified since the first reovirus-like virus was…     

白纹伊蚊抗高效氯氰菊酯和抗敌百虫品系的生物学特性及种群参数

白纹伊蚊Aedes albopictus Skuse抗高效氯氰菊酯和抗敌百虫品系的某些种群参数及生物学特性与敏感品系的比较有显著差异,两个抗药性品系之间差异也较明显。抗高效氯氰菊酯品系(Rc)的繁殖力强、平均世代历期短,雌性个体比率高。抗敌百虫品系(Rt)有适合度缺陷、平均世代历期长,雌性个体比率低。Rc和Rt的孵化率均低于敏感品系。成虫死亡率由高到低依次为Rt、Rc、S。综合分析得知,高效氯氰菊酯刺激白纹伊蚊生殖、种群增长快。抗敌百虫白纹伊蚊明显地表现出生殖不利性,种群加倍较慢。     

Three-dimensional structure of HIV-1 virus-like particles by electron cryotomography

While the structures of nearly every HIV-1 protein are known in atomic detail from X-ray crystallography and NMR spectroscopy, many questions remain about how the individual proteins are arranged in the mature infectious viral particle. Here, we report the three-dimensional structures of individual HIV-1 virus-like particles (VLPs) as obtained by electron cryotomography. These reconstructions revealed that while the structures and positions of the conical cores within each VLP were unique, they exhibited several surprisingly consistent features, including similarities in the size and shape of the wide end of the capsid (the "base"), uniform positioning of the base and other regions of the capsid 11nm away from the envelope/MA layer, a cone angle that typically varied from 24 degrees to 18 degrees around the long axis of the cone, and an internal density (presumably part of the NC/RNA complex) cupped within the base. Multiple and nested capsids were observed. These results support the fullerene cone model for the viral capsid, indicate that viral maturation involves a free re-organization of the capsid shell rather than a continuous condensation, imply that capsid assembly is both concentration-driven and template-driven, suggest that specific interactions exist between the capsid and the adjacent envelope/MA and NC/RNA layers, and show that a particular capsid shape is favored strongly in-vivo.     

Three-dimensional structure of the Chinese Sacbrood bee virus

The RNA of Chinese Sacbrood Bee Virus (CSBV) was purified and used as template to obtain a 1096 bp cDNA fragment by RT-PCR amplification. This DNA fragment was cloned into pGEM-T Easy Vector for sequencing. Analyses of the sequenced CSBV RNA fragment revealed a nucleotide sequence homology of 87.6% and a deduced amino-acid sequence homology of 94.6% with that of the Sacbrood Virus (SBV), indicating that CSBV is a different but highly homologous virus of SBV. The three-dimensional (3D) structure of CSBV was determined at 2.5 nm resolution by using electron cryo-microscopy (cryoEM) and computer reconstruction methods. The 3-D structure showed that the capsid has a T= 1 (or P= 3) icosahedral capsid shell with a smooth surface. There were 12 pentons at its icosahedral vertices (5-fold axes) and 132 holes penetrating the shell. The 3-D structure also revealed densities corresponding to the CSBV genome, suggesting icosahedrally-ordered RNA organization, a novel feature not previously reported for any picornavi     

Optimal determination of particle orientation, absolute hand, and contrast loss in single-particle electron cryomicroscopy

A computational procedure is described for assigning the absolute hand of the structure of a protein or assembly determined by single-particle electron microscopy. The procedure requires a pair of micrographs of the same particle field recorded at two tilt angles of a single tilt-axis specimen holder together with the three-dimensional map whose hand is being determined. For orientations determined from particles on one micrograph using the map, the agreement (average phase residual) between particle images on the second micrograph and map projections is determined for all possible choices of tilt angle and axis. Whether the agreement is better at the known tilt angle and axis of the microscope or its inverse indicates whether the map is of correct or incorrect hand. An increased discrimination of correct from incorrect hand (free hand difference), as well as accurate identification of the known values for the tilt angle and axis, can be used as targets for rapidly optimizing the search or refinement procedures used to determine particle orientations. Optimized refinement reduces the tendency for the model to match noise in a single image, thus improving the accuracy of the orientation determination and therefore the quality of the resulting map. The hand determination and refinement optimization procedure is applied to image pairs of the dihydrolipoyl acetyltransferase (E2) catalytic core of the pyruvate dehydrogenase complex from Bacillus stearothermophilus taken by low-dose electron cryomicroscopy. Structure factor amplitudes of a three-dimensional map of the E2 catalytic core obtained by averaging untilted images of 3667 icosahedral particles are compared to a scattering reference using a Guinier plot. A noise-dependent structure factor weight is derived and used in conjunction with a temperature factor (B=-1000A(2)) to restore high-resolution contrast without amplifying noise and to visualize molecular features to 8.7A resolution, according to a new objective criterion for resolution assessment proposed here.     

Three-dimensional structure of Bax-mediated pores in membrane bilayers

B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax) is a member of the Bcl-2 protein family having a pivotal role in triggering cell commitment to apoptosis. Bax is latent and monomeric in the cytosol but transforms into its lethal, mitochondria-embedded oligomeric form in response to cell stress, leading to the release of apoptogenic factors such as cytochrome C. Here, we dissected the structural correlates of Bax membrane insertion while oligomerization is halted. This strategy was enabled through the use of nanometer-scale phospholipid bilayer islands (nanodiscs) the size of which restricts the reconstituted system to single Bax-molecule activity. Using this minimal reconstituted system, we captured structural correlates that precede Bax homo-oligomerization elucidating previously inaccessible steps of the core molecular mechanism by which Bcl-2 family proteins regulate membrane permeabilization. We observe that, in the presence of BH3 interacting domain death agonist (Bid) BH3 peptide, Bax monomers induce the formation of ∼3.5-nm diameter pores and significantly distort the phospholipid bilayer. These pores are compatible with promoting release of ions as well as proteinaceous components, suggesting that membrane-integrated Bax monomers in the presence of Bid BH3 peptides are key functional units for the activation of the cell demolition machinery.     

Three-dimensional structure of the ciliate Didinium nasutum nucleoli

The nucleolar organization in ciliate Didinium nasutum somatic interphase nuclei was studied using serial ultrathin sections and compared for various physiological states of the cell, namely, fed ciliates, starved ciliates, and dormant cysts. It has been shown that the interphase nucleoli are large structures with a complex architecture: the fibrillar component forms an intricate network in the macronucleus space, while the granular component is located inside this network. The structures looking as individual nucleoli in single sections are actually parts of branched nucleolar networks. The intricate nucleolar networks do not disintegrate after a 30-h starvation; however, the granular component becomes denser and develops numerous cavities filled with fine fibrils of a nonribonucleoprotein nature. In fed D. nasutum, the fibrillar structures on the periphery of nucleoli contain numerous pores (virtually absent in starved cell nucleoli), which can potentially serve for transporting newly synthesized rRNP. Branched nucleolar networks are undetectable in cysts. Their nucleoli are individual structures consisting mainly of the fibrogranular component.     

Three-dimensional structure of the inner core of rice dwarf virus

Rice dwarf virus (RDV) is a double-shelled icosahedral virus. Using electron cryomicro-scopy and computer reconstruction techniques, we have determined a 3.3 nm resolution three-dimensional (3D) structure of the inner shell capsid without the outer shell and viral RNA. The results show that the inner shell is a thin, densely packed, smooth structure, which provides a scaffold for the full virus. A total of 120 copies of the major inner shell capsid protein P3 forms 60 dimers arranged in a T=1 icosahedral lattice. A close examination on the subunit packing of the T=1 inner core P3 with that of the T=13/ outer shell P8 indicated that P8 trimers connect with P3 through completely non-equivalent, yet highly specific, intermolecular interactions.     

The N-terminal domains of myosin binding protein C can bind polymorphically to F-actin

The regulation of vertebrate striated muscle contraction involves a number of different molecules, including the thin-filament accessory proteins tropomyosin and troponin that provide Ca²⁺-dependent regulation by controlling access to myosin binding sites on actin. Cardiac myosin binding protein C (cMyBP-C) appears to modulate this Ca²⁺-dependent regulation and has attracted increasing interest due to links with inherited cardiac diseases. A number of single amino acid mutations linked to clinical diseases occur in the N-terminal region of cMyBP-C, including domains C0 and C1, which previously have been shown to bind to F-actin. This N-terminal region also has been shown to both inhibit and activate actomyosin interactions in vitro. Using electron microscopy and three-dimensional reconstruction, we show that C0 and C1 can each bind to the same two distinctly different positions on F-actin. One position aligns well with the previously reported binding site that clashes with the binding of myosin to actin, but would force tropomyosin into an “on” position that exposes myosin binding sites along the filament. The second position identified here would not interfere with either myosin binding or tropomyosin positioning. It thus appears that the ability to bind to at least two distinctly different positions on F-actin, as observed for tropomyosin, may be more common than previously considered for other actin binding proteins. These observations help to explain many of the seemingly contradictory results obtained with cMyBP-C and show how cMyBP-C can provide an additional layer of regulation to actin-myosin interactions. They also suggest a redundancy of C0 and C1 that may explain the absence of C0 in skeletal muscle.     

Three-dimensional computer reconstructions from serial sections of cell nuclei

The analysis of ultrathin serial sections as 3-dimensional (3D) information requires interpretation and display of a large amount of data. We suggest a simple way to solve this problem; it permits presentation of a series of sections as a 3D color image of good quality. It involves a picture system with specialized hardware and software written for this purpose. 3D images of cellular organelles have been drawn either by manually defining the contour of the objects or by thresholding of the volumes in the structures. These 2 methods allow rapid drawing of the image on the screen. It is possible to determine the position, shape and size of 3D structures. This interactive system allows the user to choose between several options: colors, removal of parts of the object, and cutout.     

Isolation of Rickettsia felis in the mosquito cell line C6/36

We report the isolation and establishment of Rickettsia felis in the C6/36 cell line. Rickettsial growth was intense, always with 90 to 100% of cells being infected after few weeks. The rickettsial isolate was confirmed by testing infected cells by PCR and sequencing fragments of three major Rickettsia genes (gltA, ompB, and the 17-kDa protein gene).     

Three-dimensional structure of basal body triplet revealed by electron cryo-tomography

Basal bodies and centrioles play central roles in microtubule (MT)‐organizing centres within many eukaryotes. They share a barrel‐shaped cylindrical structure composed of nine MT triplet blades. Here, we report the structure of the basal body triplet at 33 Å resolution obtained by electron cryo‐tomography and 3D subtomogram averaging. By fitting the atomic structure of tubulin into the EM density, we built a pseudo‐atomic model of the tubulin protofilaments at the core of the triplet. The 3D density map reveals additional densities that represent non‐tubulin proteins attached to the triplet, including a large inner circular structure in the basal body lumen, which functions as a scaffold to stabilize the entire basal body barrel. We found clear longitudinal structural variations along the basal body, suggesting a sequential and coordinated assembly mechanism. We propose a model in which δ‐tubulin and other components participate in the assembly of the basal body.     

Stable expression of insect GABA receptors in insect cell lines promoters for efficient expression of Drosophila and mosquito Rdl GABA receptors in stably transformed mosquito cell lines

We are interested in establishing stably transformed insect cell lines efficiently expressing the insect γ-aminobutyric acid (GABA) receptor subunit gene Resistance to dieldrin or Rdl. In order to facilitate this we utilized a system based on stable transformation of Aedes albopictus mosquito cell lines using the dihydrofolate reductase (dhfr) gene as a selectable marker. Here we report the production of stable mosquito cell lines carrying high copy numbers of Rdl genes from both Drosophila and Aedes aegypti mosquitoes and the subsequent high efficiency expression of functional GABA gated chloride ion channels. We also used this system to compare the activity of a range of immediate early baculovirus promoters in mosquito cell culture and demonstrate that IE1 promoter constructs work efficiently across insect species. Results are discussed in relation to the potential use of these constructs in the genetic transformation of non-Drosophilid insects.