排序方式: 共有90条查询结果,搜索用时 15 毫秒
1.
Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
RK Draper D Chin D Eurey-Owens IE Scheffler MI Simon 《The Journal of cell biology》1979,83(1):116-125
We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells. 相似文献
2.
3.
Measles virus (MeV), a member of the paramyxovirus family of enveloped RNA viruses and one of the most infectious viral pathogens identified, accounts for major pediatric morbidity and mortality worldwide although coordinated efforts to achieve global measles control are in place. Target cell entry is mediated by two viral envelope glycoproteins, the attachment (H) and fusion (F) proteins, which form a complex that achieves merger of the envelope with target cell membranes. Despite continually expanding knowledge of the entry strategies employed by enveloped viruses, our molecular insight into the organization of functional paramyxovirus fusion complexes and the mechanisms by which the receptor binding by the attachment protein triggers the required conformational rearrangements of the fusion protein remain incomplete. Recently reported crystal structures of the MeV attachment protein in complex with its cellular receptors CD46 or SLAM and newly developed functional assays have now illuminated some of the fundamental principles that govern cell entry by this archetype member of the paramyxovirus family. Here, we review these advances in our molecular understanding of MeV entry in the context of diverse entry strategies employed by other members of the paramyxovirus family. 相似文献
4.
In the present study, we used osteoprotegerin (OPG), which blocks osteoclastogenesis, to correct and thus explain the hypercalcemia that is seen during dietary Mg deficiency in the mouse. Control and Mg-deficient mice received injections for 12 days of either OPG or vehicle only. Serum Ca was similar in Mg-deficient mice treated with OPG and in control mice receiving OPG (9.2±0.3 mg/dl vs. 9.2±0.5). Both groups had significantly higher serum Ca than controls or Mg-deficient animals receiving vehicle alone. Surprisingly, Mg-depleted mice that received OPG in doses that inhibit osteoclastic bone resorption remained hypercalcemic. Because mature osteoclasts still present in the marrow might be hyperactive, we examined osteoclast morphology at the light microscopic and ultrastructural level. Light microscopic examination of trabecular bone showed few osteoclasts in OPG-treated mice. Ultrastructural examination revealed that osteoclasts in OPG-treated mice have decreased contact with the endosteal bone surface and absence of a ruffled border. Because the morphology of the existing pool of mature osteoclasts did not enhance resorption, another mechanism, such as increased intestinal absorption of Ca in Mg-deficient mice, likely contributes to the hypercalcemia observed during Mg deficiency. 相似文献
5.
Maino Tahara Yuri Ito Melinda A. Brindley Xuemin Ma Jilan He Songtao Xu Hideo Fukuhara Kouji Sakai Katsuhiro Komase Paul A. Rota Richard K. Plemper Katsumi Maenaka Makoto Takeda 《Journal of virology》2013,87(1):666-675
Effective vaccination programs have dramatically reduced the number of measles-related deaths globally. Although all the available data suggest that measles eradication is biologically feasible, a structural and biochemical basis for the single serotype nature of measles virus (MV) remains to be provided. The hemagglutinin (H) protein, which binds to two discrete proteinaceous receptors, is the major neutralizing target. Monoclonal antibodies (MAbs) recognizing distinct epitopes on the H protein were characterized using recombinant MVs encoding the H gene from different MV genotypes. The effects of various mutations on neutralization by MAbs and virus fitness were also analyzed, identifying the location of five epitopes on the H protein structure. Our data in the present study demonstrated that the H protein of MV possesses at least two conserved effective neutralizing epitopes. One, which is a previously recognized epitope, is located near the receptor-binding site (RBS), and thus MAbs that recognize this epitope blocked the receptor binding of the H protein, whereas the other epitope is located at the position distant from the RBS. Thus, a MAb that recognizes this epitope did not inhibit the receptor binding of the H protein, rather interfered with the hemagglutinin-fusion (H-F) interaction. This epitope was suggested to play a key role for formation of a higher order of an H-F protein oligomeric structure. Our data also identified one nonconserved effective neutralizing epitope. The epitope has been masked by an N-linked sugar modification in some genotype MV strains. These data would contribute to our understanding of the antigenicity of MV and support the global elimination program of measles. 相似文献
6.
Stefanie A. Krumm Makoto Takeda Richard K. Plemper 《The Journal of biological chemistry》2013,288(41):29943-29953
Paramyxovirus genomes are ribonucleoprotein (RNP) complexes consisting of nucleoprotein (N)-encapsidated viral RNA. Measles virus (MeV) N features an amino-terminal RNA-binding core and a 125-residue tail domain, of which only the last 75 residues are considered fully mobile on the nucleocapsid surface. A molecular recognition element (MoRE) domain mediates binding of the viral phosphoprotein (P). This P N-tail interaction is considered instrumental for recruiting the polymerase complex to the template. We have engineered MeV N variants with tail truncations progressively eliminating the MoRE domain and upstream tail sections. Confirming previous reports, RNPs with N truncations lacking the carboxyl-terminal 43-residues harboring the MoRE domain cannot serve as polymerase template. Remarkably, further removal of all tail residues predicted to be surface-exposed significantly restores RNP bioactivity. Insertion of structurally dominant tags into the central N-tail section reduces bioactivity, but the negative regulatory effect of exposed N-tail stems is sequence-independent. Bioactive nucleocapsids lacking exposed N-tail sections are unable to sustain virus replication, because of weakened interaction of the advancing polymerase complex with the template. Deletion of the N-MoRE-binding domain in P abrogates polymerase recruitment to standard nucleocapsids, but polymerase activity is partially restored when N-tail truncated RNPs serve as template. Revising central elements of the current replication model, these data reveal that MeV polymerase is capable of productively docking directly to the nucleocapsid core. Dispensable for polymerase recruitment, N-MoRE binding to P-tail stabilizes the advancing polymerase-RNP complex and may rearrange unstructured central tail sections to facilitate polymerase access to the template. 相似文献
7.
Pakistan, the second most populous Muslim nation in the world, has started to finally experience and confront the HIV/AIDS epidemic. The country had been relatively safe from any indigenous HIV cases for around two decades, with most of the infections being attributable to deported HIV positive migrants from the Gulf States. However, the virus finally seems to have found a home-base, as evidenced by the recent HIV outbreaks among the injection drug user community. Extremely high-risk behavior has also been documented among Hijras (sex workers) and long-distance truck drivers. The weak government response coupled with the extremely distressing social demographics of this South-Asian republic also helps to compound the problem. The time is ripe now to prepare in advance, to take the appropriate measures to curtail further spread of the disease. If this opportunity is not utilized right now, little if at all could be done later. 相似文献
8.
9.
Single-chain antibody displayed on a recombinant measles virus confers entry through the tumor-associated carcinoembryonic antigen
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hammond AL Plemper RK Zhang J Schneider U Russell SJ Cattaneo R 《Journal of virology》2001,75(5):2087-2096
To redirect the tropism of the vaccine strain of measles virus (MV), Edmonston B, to a targeted cell population, we displayed on the viral hemagglutinin (H) a single-chain antibody (scAb) specific for the tumor-associated carcinoembryonic antigen (CEA). We generated H fusion proteins with three forms of the scAb appended, differing in the lengths of the linkers separating the VH and VL domains and thus in the oligomerization states of the scAbs. All proteins were stable, appeared properly folded, and were transported to the cell surface, but only H displaying the long-linker form of scAb was functional in supporting cell-cell fusion. This protein induced extensive syncytia in cells expressing the normal virus receptor CD46 and also in CD46-negative cells expressing the targeted receptor, human CEA. Replication-competent MV with H replaced by H displaying the long-linker form of scAb was recovered and replicated efficiently in both CD46-positive and CD46-negative, CEA-positive cells. Thus, MV not only tolerates the addition of a scAb on its H protein but also infects cells via a novel interaction between the scAb and its targeted receptor. 相似文献
10.
Mutations in the putative HR-C region of the measles virus F2 glycoprotein modulate syncytium formation
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The fusion (F) glycoproteins of measles virus strains Edmonston (MV-Edm) and wtF (MV-wtF) confer distinct cytopathic effects and strengths of hemagglutinin (H) interaction on a recombinant MV-Edm virus. They differ in just two amino acids, V94 and V101 in F-Edm versus M94 and F101 in F-wtF, both of which lie in the relatively uncharacterized F(2) domain. By comparing the sequence of MV F with those of the parainfluenza virus SV5 and Newcastle disease virus (NDV) F proteins, the structures of which are known, we show that MV F(2) also possesses a potential heptad repeat (HR) C domain. In NDV, the N-terminal half of HR-C interacts with HR-A in F(1) while the C-terminal half is induced to kink outward by a central proline residue. We found that this proline is part of an LXP motif conserved in all three viruses. Folding and transport of MV F require this motif to be intact and also require covalent interaction of cysteine residues that probably support the potential HR-A-HR-C interaction. Amino acids 94 and 101, both located in "d" positions of the HR-C helical wheel, lie in the potentially outwardly kinked region. We demonstrate that their effect on MV fusogenicity and glycoprotein interaction is mediated solely by amino acid 94. Substitutions at position 94 with polar or charged amino acids are tolerated poorly or not at all, while changes to smaller and more hydrophilic amino acids are tolerated in both transiently expressed F protein and recombinant virus. MV F V94A and MV F V94G viruses induce extensive syncytium formation and are relatively, or almost completely, resistant to a known inhibitor of MV glycoprotein-induced fusion. We propose that the conformational changes in MV F protein required to expose the fusion peptide involve the C-terminal half of the HR-C helix, specifically amino acid 94. 相似文献