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Results for “viral complexity”

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At least 775 records · Page 43Linked to original sources

PubMed1997

HIV-1 protein gp120 crosses the blood-brain barrier: role of adsorptive endocytosis.

HIV-1 infects the brain and leads to AIDS dementia complex. The viral coat glycoprotein, gp120, may facilitate the passage of HIV-1 and HIV-infected immune cells across the blood-brain barrier (BBB). Since the endothelial cells of the BBB do not possess the CD4 or galactosylceramide binding sites used by gp120 to induce HIV-1 uptake into other cell types, how gp120 mediates entry into brain is unknown. We postulate that gp120 crosses the BBB and does so by acting as a weak lectin to induce adsorptive endocytosis (AE) in a fashion similar to other glycoproteins like wheatgerm agglutinin (WGA). We found in vivo that gp120 crosses the BBB and its passage is enhanced 18.7-fold by WGA. In vitro studies confirm that WGA enhances uptake of gp120 by brain endothelia; most of the uptake is membrane-associated, as expected in AE. Uptake is not dependent on clatharin, caveolae, calcium channels, or endosomal acidification. Our results suggest that gp120 crosses the BBB and does so by acting as a lectin to induce AE.

Adsorption↗

PubMed2005

Pharmacokinetics of Plasmid DNA-Based Non-viral Gene Medicine.

Non-viral gene therapy can be realized by optimization of the pharmacokinetic properties of both the vector and the encoded therapeutic protein. A major obstacle to its successful clinical application is the limited ability of plasmid DNA, the most convenient gene-coding compound, to distribute within the body after in vivo administration. Under normal conditions, plasmid DNA and its non-viral vector complexes have difficulty in passing through various anatomical and biological barriers. These characteristics greatly limit the number and distribution of cells transduced with the vector, because transgene expression only occurs in cells that are reached by the vector. New approaches to the design of vectors as well as the methods of administration, such as electroporation and a hydrodynamic delivery, have increased the transgene expression in vivo, suggesting that improved distribution of plasmid DNA is possible by these approaches. In this chapter, the basic pharmacokinetic properties of naked plasmid DNA under normal conditions are first reviewed, then the properties of both naked and complexed plasmid DNA are discussed under conditions where significant transgene expression takes place.

Journal Article↗

PubMed2003

Manipulation of cell surface macromolecules by flaviviruses.

Cell surface macromolecules play a crucial role in the biology and pathobiology of flaviviruses, both as receptors for virus entry and as signaling molecules for cell-cell interactions in the processes of vascular permeability and inflammation. This review examines the cell tropism and pathogenesis of flaviviruses from the standpoint of cell surface molecules, which have been implicated as receptors in both virus-cell as well as cell-cell interactions. The emerging picture is one that encompasses extensive regulation and interplay among the invading virus, viral immune complexes, Fc receptors, major histocompatibility complex antigens, and adhesion molecules.

Animals↗

PubMed1997

Antiviral activity of an extract from leaves of the tropical plant Acanthospermum hispidum.

Incubation of the alphaherpesviruses pseudorabiesvirus (PRV) and bovine herpesvirus 1 during infection of cell cultures with an extract prepared from the leaves of Acanthospermum hispidum impaired productive replication of these viruses in a concentration-dependent manner whereas propagation of classical swine fever virus, foot-and-mouth disease virus and vaccinia virus was not affected. The 50% inhibitory concentration for cell growth (IC50) was 107 +/- 5 microliters/ml, and the concentration reducing PRV yield by 1 log10 (90% effective concentration, EC90) was 8 +/- 3 microliters/ml. The selectivity index calculated as the IC50/EC90 ration was 13 +/- 4. Delineation of the mechanism of the antiviral activity demonstrated inhibition of alphaherpesvirus attachment to and, to a lesser extent, penetration into the cells. In contrast, viral gene expression was not inhibited by the extract when added after entry of virions into the target cells. Reduced antiviral activity of A.h. against PRV deletion mutants lacking glycoprotein C (gC) or glycoproteins gC, gE, gG and gI altogether indicated that gC alone and/or viral attachment complexes of which gC is a component constitute the target structures for A. hispidum.

Animals↗

PubMed2004

Microbial mimics are major targets of crossreactivity with human pyruvate dehydrogenase in primary biliary cirrhosis.

BACKGROUND/AIMS: Previous studies on patients with primary biliary cirrhosis (PBC) have shown extensive cross-reactivity between the dominant B- and T-cell epitopes of human pyruvate dehydrogenase complex-E2 (PDC-E2), and microbial mimics. Such observations have suggested microbial infection as having a role in the induction of anti-mitochondrial antibodies, through a mechanism of molecular mimicry. However the biological significance of these cross-reactivities is questionable, because PDC-E2 is so highly conserved among various species. METHODS: Interrogating protein databases, ten non-PDC-E2 microbial sequences with high degree of similarity to PDC-E2(212-226) were found in Escherichia coli (6), Helicobacter pylori, Pseudomonas aeruginosa, Cytomegalovirus, and Haemophilus influenzae. We report on a study testing reactivity and competitive cross-reactivity against these respective peptides, and in some cases the parent protein, using sera from 55 patients with PBC, compared to reactivity of 190 pathological and 28 healthy controls. RESULTS: Cross-reactivity to E. coli mimics was commonly seen in PBC, and in a subset of pathological controls except where there was no evidence of urinary tract infection and correlated with anti-mitochondrial reactivity. CONCLUSIONS: E. coli/PDC-E2 cross-reactive immunity characterizes primary biliary cirrhosis; the large number of E. coli immunogenic mimics may account for the dominance of the major PDC-E2 autoepitope.

Adult↗

PubMed2004

Apoptosis and immune responses to self.

The mystery that surrounds autoimmunity revolves around how the immune system of patients who have systemic autoimmune diseases becomes primed to recognize intracellular antigens, how the autoantibodies thus produced contribute to the pathogenesis of the disease, and how those autoantibodies access their target proteins. By examining the mechanisms that are involved in the normal cellular process of apoptosis, we are beginning to unravel this mystery. The intracellular autoantigen targets of many systemic autoimmune diseases become altered during apoptosis in ways that may change how they are perceived by the immune system. High concentrations of self-antigens, or in the case of viral infection, complexes of foreign and self-antigens, are packaged during generation of apoptotic cells. The packages also may contain altered fragments of self-antigens that have not been encountered previously by the immune system. Under normal circumstances, apoptotic cells are cleared rapidly by macrophages and DCs. The normal consequence of that clearance is that the apoptosis-altered self-antigens are either ignored by the immune system or tolerance to those antigens is maintained. Clearance is achieved through complex mechanisms that enable macrophages and DCs to recognize apoptotic cells as nonthreatening "self" particles. Defects in this process that cause a delay in clearance could change the appearance of apoptotic cells and cause them to be recognized as "foreign invaders," thereby stimulating an inflammatory response that, in turn, activates an immune response to self-antigens. By studying the mechanisms that are involved in recognition and clearance of apoptotic cells, we are uncovering clues to the defects that may underlie the development of systemic autoimmunity.

Animals↗

PubMed2001

Dynamin family of mechanoenzymes.

The dynamin family of proteins is continually growing, and in recent years members have been localized to areas of mitochondrial fission, plant phragmoplasts and chloroplasts, and viral ribonucleoprotein complexes. All the dynamin-like proteins examined to-date appear to assemble into oligomers, such as rings or spirals; however, it remains to be determined if a global mechanism of action exists. Even the role of dynamin in vesicle formation remains controversial as to whether it behaves as a molecular switch or as a mechanochemical enzyme.

Animals↗

PubMed2002

Slipping through the door: HIV entry into the nucleus.

HIV infection of non-dividing cellular targets like macrophages requires successful passage of the viral preintegration complex (PIC) across an intact nuclear envelope. Unique but redundant nuclear import signals reside within the HIV integrase, matrix, and Vpr proteins as well as the 'DNA flap'; these signals appear to facilitate PIC transport through the limiting nuclear pores. We discuss recent studies that have advanced our understanding of this key step in the HIV life cycle.

HIV Infections↗

PubMed1996

Positional cloning of the mouse retrovirus restriction gene Fv1.

Vertebrate evolution has taken place against a background of constant retrovirus infection, and much of the mammalian genome consists of endogenous retrovirus-like elements. Several host genes have evolved to control retrovirus replication, including Friend-virus-susceptibility-1, Fv1, on mouse chromosome 4 (refs 3, 4). The Fv1 gene acts on murine leukaemia virus at a stage after entry into the target cell but before integration and formation of the provirus. Although restriction is not absolute, Fv1 prevents or delays spontaneous or experimentally induced viral tumours. In vitro, Fv1 restriction leads to an apparent 50-1,000 fold reduction in viral titre. Genetic evidence implicates a direct interaction between the Fv1 gene product and a component of the viral preintegration complex, the capsid protein CA (refs 7-9). We have now cloned Fv1: the gene appears to be derived from the gag region of an endogenous retrovirus unrelated to murine leukaemia virus, implying that the Fv1 protein and its target may share functional similarities despite the absence of nucleotide-sequence homology.

Amino Acid Sequence↗

PubMed1996

A nucleotide-flipping mechanism from the structure of human uracil-DNA glycosylase bound to DNA.

Any uracil bases in DNA, a result of either misincorporation or deamination of cytosine, are removed by uracil-DNA glycosylase (UDG), one of the most efficient and specific of the base-excision DNA-repair enzymes. Crystal structures of human and viral UDGs complexed with free uracil have indicated that the enzyme binds an extrahelical uracil. Such binding of undamaged extrahelical bases has been seen in the structures of two bacterial methyltransferases and bacteriophage T4 endonuclease V. Here we characterize the DNA binding and kinetics of several engineered human UDG mutants and present the crystal structure of one of these, which to our knowledge represents the first structure of any eukaryotic DNA repair enzyme in complex with its damaged, target DNA. Electrostatic orientation along the UDG active site, insertion of an amino acid (residue 272) into the DNA through the minor groove, and compression of the DNA backbone flanking the uracil all result in the flipping-out of the damaged base from the DNA major groove, allowing specific recognition of its phosphate, deoxyribose and uracil moieties. Our structure thus provides a view of a productive complex specific for cleavage of uracil from DNA and also reveals the basis for the enzyme-assisted nucleotide flipping by this critical DNA-repair enzyme.

Crystallography, X-Ray↗

PubMed2003

The antiretroviral enzyme APOBEC3G is degraded by the proteasome in response to HIV-1 Vif.

The human protein apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like-3G (APOBEC3G), also known as CEM-15, mediates a newly described form of innate resistance to retroviral infection by catalyzing the deamination of deoxycytidine to deoxyuridine in viral cDNA replication intermediates. Because DNA deamination takes place after virus entry into target cells, APOBEC3G function is dependent on its association with the viral nucleoprotein complexes that synthesize cDNA and must therefore be incorporated into virions as they assemble in infected cells. Here we show that the HIV-1 virion infectivity factor (Vif) protein protects the virus from APOBEC3G-mediated inactivation by preventing its incorporation into progeny virions, thus allowing the ensuing infection to proceed without DNA deamination. In addition to helping exclude APOBEC3G from nascent virions, Vif also removes APOBEC3G from virus-producing cells by inducing its ubiquitination and subsequent degradation by the proteasome. Our findings indicate that pharmacologic strategies aimed at stabilizing APOBEC3G in HIV-1 infected cells should be explored as potential HIV/AIDS therapeutics.

APOBEC-3G Deaminase↗

PubMed1996

NAP-I is a functional homologue of TAF-I that is required for replication and transcription of the adenovirus genome in a chromatin-like structure.

BACKGROUND: For the activation of replication and transcription from DNA in a chromatin structure, a variety of factors are thought to be needed that alter the chromatin structure. Template activating factor-I (TAF-I) has been identified as such a host factor required for replication of the adenovirus (Ad) genome complexed with viral basic core proteins (Ad core). TAF-I also stimulates transcription from the Ad core DNA. RESULTS: Using mutant TAF-I proteins, we have demonstrated that the acidic stretch present in the carboxyl terminal region is essential for the stimulation of transcription from the Ad core. A genomic footprinting experiment with restriction endonuclease has revealed that TAF-I causes a structural change in the Ad core. TAF-I has been shown to have significant amino acid similarity to nucleosome assembly protein-I (NAP-I), which is involved in the formation of the chromatin structure. We have shown that TAF-I can be substituted by NAP-I in the activation of the cell-free Ad core transcription system. Two of the tripartite acidic regions and the region homologous to TAF-I in NAP-I are required for the maximal TAF-I activity of NAP-I. Furthermore, TAF-I has been shown to have NAP-I activity, and the acidic region of TAF-I is required for this activity. CONCLUSIONS: Since TAF-I causes the structural change of the Ad core and thereby activates transcription, TAF-I is thought to be one of the proteins which is involved in chromatin remodeling. NAP-I is structurally related to TAF-I and functionally substitutes for TAF-I. Furthermore, TAF-I has NAP-I activity. These observations suggest that this type of molecule has dual functions, possibly by participating in facilitating the assembly of the chromatin structure as well as perturbing the chromatin structure to allow transcription to proceed.

Adenoviridae↗

PubMed1998

Are minichromosomes valid model systems for DNA replication control? Lessons learned from Escherichia coli.

Initiation of chromosome replication is a key event in the life cycle of any organism. Little is known, however, about the regulatory mechanisms of this vital process. Conventionally, the initiation mechanism of chromosome replication in microorganisms has been studied using plasmids in which an origin of chromosome replication has been cloned, rather than using the chromosome itself. The reason for this is that even bacterial chromosomes are so large that biochemical and genetic manipulations become difficult and cumbersome. Recently, the combination of flow cytometry and genetic methods, in which modifications of the replication origin are systematically introduced onto the chromosome, has made possible detailed studies of the molecular events involved in the control of replication initiation in Escherichia coli. The results indicate that requirements for initiation at the chromosomal origin, oriC, are drastically different from those for initiation at cloned oriC.

Chromosomes, Bacterial↗

PubMed2002

Strand-specific loading of DnaB helicase by DnaA to a substrate mimicking unwound oriC.

We analysed the enzymatic activity (strand dis-placement) of the Escherichia coli DnaB helicase on a mirror-image pair of oligonucleotide-based substrates mimicking the unwound replication origin oriC. Loading of the helicase complex occurred exclusively to the single-stranded 'lower strand' part of the substrates. Full helicase activity required DnaA bound to the double-stranded part of the substrates (oriC DnaA box R1) and to their single-stranded 'upper strand' part. We assume that in vivo DnaA also loads the first of two helicase complexes - required for the assembly of two replication forks - to the lower strand of oriC during initiation of bidirectional chromosome replication in E. coli.

Bacterial Proteins↗

PubMed2004

The severe acute respiratory syndrome-coronavirus replicative protein nsp9 is a single-stranded RNA-binding subunit unique in the RNA virus world.

The recently identified etiological agent of the severe acute respiratory syndrome (SARS) belongs to Coronaviridae (CoV), a family of viruses replicating by a poorly understood mechanism. Here, we report the crystal structure at 2.7-A resolution of nsp9, a hitherto uncharacterized subunit of the SARS-CoV replicative polyproteins. We show that SARS-CoV nsp9 is a single-stranded RNA-binding protein displaying a previously unreported, oligosaccharide/oligonucleotide fold-like fold. The presence of this type of protein has not been detected in the replicative complexes of RNA viruses, and its presence may reflect the unique and complex CoV viral replication/transcription machinery.

Amino Acid Sequence↗

PubMed2005

The viral polymerase mediates adaptation of an avian influenza virus to a mammalian host.

Mammalian influenza viruses are descendants of avian strains that crossed the species barrier and underwent further adaptation. Since 1997 in southeast Asia, H5N1 highly pathogenic avian influenza viruses have been causing severe, even fatal disease in humans. Although no lineages of this subtype have been established until now, such repeated events may initiate a new pandemic. As a model of species transmission, we used the highly pathogenic avian influenza virus SC35 (H7N7), which is low-pathogenic for mice, and its lethal mouse-adapted descendant SC35M. Specific mutations in SC35M polymerase considerably increase its activity in mammalian cells, correlating with high virulence in mice. Some of these mutations are prevalent in chicken and mammalian isolates, especially in the highly pathogenic H5N1 viruses from southeast Asia. These activity-enhancing mutations of the viral polymerase complex demonstrate convergent evolution in nature and, therefore, may be a prerequisite for adaptation to a new host paving the way for new pandemic viruses.

Adaptation, Physiological↗

PubMed1987

Binding of the virion protein mediating alpha gene induction in herpes simplex virus 1-infected cells to its cis site requires cellular proteins.

In herpes simplex virus 1-infected cells, the transcription of alpha genes, the first set of genes to be expressed, is induced by a virion component, the alpha-trans-induction factor, and requires a cis site. Homologs of the cis site are present in the promoter-regulatory domains of all alpha genes and bind two cellular proteins designated as alpha H1 and alpha H2-alpha H3. We report that alpha-trans-induction factor, synthesized in vitro or present in nuclear extracts of infected cells, forms complexes with viral DNA fragments containing its cis-acting site only in the presence of cellular proteins and only under conditions that also enable the binding of the alpha H1 protein to the DNA. The induction of alpha genes by alpha-trans-induction factor appears, therefore, to be mediated by the interaction of the viral protein with cellular proteins at its cis-acting site.

Binding Sites↗

PubMed1995

Replication factor encoded by a putative oncogene, set, associated with myeloid leukemogenesis.

DNA replication of the adenovirus genome complexed with viral core proteins is dependent on the host factor designated template activating factor I (TAF-I) in addition to factors required for replication of the naked genome. Recently, we have purified TAF-I as 39- and 41-kDa polypeptides from HeLa cells. Here we describe the cloning of two human cDNAs encoding TAF-I. Nucleotide sequence analysis revealed that the 39-kDa polypeptide corresponds to the protein encoded by the set gene, which is the part of the putative oncogene associated with acute undifferentiated leukemia when translocated to the can gene. The 41-kDa protein contains the same amino acid sequence as the 39-kDa protein except that short N-terminal regions differ in both proteins. Recombinant proteins, which were purified from extracts of Escherichia coli, expressing the proteins from cloned cDNAs, possessed TAF-I activities in the in vitro replication assay. A particular feature of TAF-I proteins is the presence of a long acidic tail in the C-terminal region, which is thought to be an essential part of the SET-CAN fusion protein. Studies with mutant TAF-I proteins devoid of this acidic region indicated that the acidic region is essential for TAF-I activity.

Amino Acid Sequence↗