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Viral Entry (viral + entry)
Selected AbstractsCome in and take your coat off , how host cells provide endocytosis for virus entryCELLULAR MICROBIOLOGY, Issue 10 2010Mario Schelhaas Summary Viruses are intracellular parasites that rely upon the host cell machinery for their life cycle. Newly generated virus particles have to transmit their genomic information to uninfected cells/organisms. Viral entry is the process to gain access to viral replication sites within uninfected cells, a multistep course of events that starts with binding to target cells. Since viruses are simple in structure and composition and lack any locomotive capacity, viruses depend on hundreds of host cell proteins during entry. Most animal viruses take advantage of endocytosis to enter cells. Cell biological, morphological and biochemical studies, live cell imaging and systematic approaches have identified various new endocytic mechanisms besides clathrin-mediated endocytosis, macropinocytosis and caveolar/lipid raft-mediated endocytosis. Hence, studying virus entry has become ever more complex. This review provides a cell biological overview of the existing endocytic mechanisms and strategies used or potentially used by viruses to enter cells. [source] Crystal structures of Nipah and Hendra virus fusion core proteinsFEBS JOURNAL, Issue 19 2006Zhiyong Lou The Nipah and Hendra viruses are highly pathogenic paramyxoviruses that recently emerged from flying foxes to cause serious disease outbreaks in humans and livestock in Australia, Malaysia, Singapore and Bangladesh. Their unique genetic constitution, high virulence and wide host range set them apart from other paramyxoviruses. These characteristics have led to their classification into the new genus Henpavirus within the family Paramyxoviridae and to their designation as Biosafety Level 4 pathogens. The fusion protein, an enveloped glycoprotein essential for viral entry, belongs to the family of class I fusion proteins and is characterized by the presence of two heptad repeat (HR) regions, HR1 and HR2. These two regions associate to form a fusion-active hairpin conformation that juxtaposes the viral and cellular membranes to facilitate membrane fusion and enable subsequent viral entry. The Hendra and Nipah virus fusion core proteins were crystallized and their structures determined to 2.2 Å resolution. The Nipah and Hendra fusion core structures are six-helix bundles with three HR2 helices packed against the hydrophobic grooves on the surface of a central coiled coil formed by three parallel HR1 helices in an oblique antiparallel manner. Because of the high level of conservation in core regions, it is proposed that the Nipah and Hendra virus fusion cores can provide a model for membrane fusion in all paramyxoviruses. The relatively deep grooves on the surface of the central coiled coil represent a good target site for drug discovery strategies aimed at inhibiting viral entry by blocking hairpin formation. [source] Altering the surface properties of baculovirus Autographa californica NPV by insertional mutagenesis of the envelope protein gp64FEBS JOURNAL, Issue 18 2002Alexandra Spenger The envelope protein gp64 of the baculovirus Autographa californica nuclear polyhedrosis virus is essential for viral entry into insect cells, as the glycoprotein both mediates pH-dependent membrane fusion and binds to host cell receptors. Surface modification of baculovirus particles by genetic engineering of gp64 has been demonstrated by various strategies and thus has become an important and powerful tool in molecular biology. To improve further the presentation of peptides on the surface of baculovirus particles, several insertion sites within the gp64 envelope protein were selected by their theoretical maximum surface probability and investigated for efficient peptide presentation. The ELDKWA peptide of the gp41 of HIV-1, specific for the human mAb 2F5, was inserted into 17 different positions of the glycoprotein gp64. Propagation of viruses was successful in 13 cases, mutagenesis at four positions did not result in production of intact virus particles. Western blotting, FACS analysis and ELISA were used for characterization of the different binding properties of the mutants. Insertion of this peptide into the native envelope protein resulted in high avidity display on the surface of baculovirus particles. This approach offers the possibility of effective modification of surface properties in regard to host range specificity and antigen display. [source] Isolated human astrocytes are not susceptible to infection by M- and T-tropic HIV-1 strains despite functional expression of the chemokine receptors CCR5 and CXCR4 ,GLIA, Issue 3 2001Agnès Boutet Abstract Within the brain, HIV-1 targets the microglia and astrocytes. Previous studies have reported that viral entry into astrocytes is independent of CD4, in contrast to microglia. We aimed to determine whether chemokine receptors play a role in mediating CD4-independent HIV-1 entry into astrocytes. We found that embryonic astrocytes and microglial cells express CCR5, CCR3, and CXCR4 transcripts. Intracellular calcium levels in astrocytes were found to increase following application of RANTES, MIP-1, (CCR5-agonist), SDF-1, (CXCR4-agonist), but not eotaxin (CCR3-agonist). In microglial cells, eotaxin was also able to modulate internal calcium homeostasis. CD4 was not present at the cell surface of purified astrocytes but CD4 mRNA could be detected by RT-PCR. Neither HIV-19533 (R5 isolate) nor HIV-1LAI (X4 isolate) penetrated into purified astrocytes. In contrast, mixed CNS cell cultures were infected by HIV-19533 and this was inhibited by anti-CD4 mAb in 4/4 tested cultures and by anti-CCR5 mAb in 2/4. Thus, the HIV-1 R5 strain requires CD4 to penetrate into brain cells, suggesting that CCR5 cannot be used as the primary receptor for M-tropic HIV-1 strains in astrocytes. Moreover, inconstant inhibition of HIV-1 entry by anti-CCR5 mAb supports the existence of alternative coreceptors for penetration of M-tropic isolates into brain cells. GLIA 34:165,177, 2001. © 2001 Wiley-Liss, Inc. [source] Novel mechanism of antibodies to hepatitis B virus in blocking viral particle release from cells,HEPATOLOGY, Issue 3 2010Avidan U. Neumann Antibodies are thought to exert antiviral activities by blocking viral entry into cells and/or accelerating viral clearance from circulation. In particular, antibodies to hepatitis B virus (HBV) surface antigen (HBsAg) confer protection, by binding circulating virus. Here, we used mathematical modeling to gain information about viral dynamics during and after single or multiple infusions of a combination of two human monoclonal anti-HBs (HepeX-B) antibodies in patients with chronic hepatitis B. The antibody HBV-17 recognizes a conformational epitope, whereas antibody HBV-19 recognizes a linear epitope on the HBsAg. The kinetic profiles of the decline of serum HBV DNA and HBsAg revealed partial blocking of virion release from infected cells as a new antiviral mechanism, in addition to acceleration of HBV clearance from the circulation. We then replicated this approach in vitro, using cells secreting HBsAg, and compared the prediction of the mathematical modeling obtained from the in vivo kinetics. In vitro, HepeX-B treatment of HBsAg-producing cells showed cellular uptake of antibodies, resulting in intracellular accumulation of viral particles. Blocking of HBsAg secretion also continued after HepeX-B was removed from the cell culture supernatants. Conclusion: These results identify a novel antiviral mechanism of antibodies to HBsAg (anti-HBs) involving prolonged blocking of the HBV and HBsAg subviral particles release from infected cells. This may have implications in designing new therapies for patients with chronic HBV infection and may also be relevant in other viral infections. (HEPATOLOGY 2010;) [source] A comparative molecular force spectroscopy study of homophilic JAM-A interactions and JAM-A interactions with reovirus attachment protein ,1JOURNAL OF MOLECULAR RECOGNITION, Issue 4 2008Sri Ram Krishna Vedula Abstract JAM-A belongs to a family of immunoglobulin-like proteins called junctional adhesion molecules (JAMs) that localize at epithelial and endothelial intercellular tight junctions. JAM-A is also expressed on dendritic cells, neutrophils, and platelets. Homophilic JAM-A interactions play an important role in regulating paracellular permeability and leukocyte transmigration across epithelial monolayers and endothelial cell junctions, respectively. In addition, JAM-A is a receptor for the reovirus attachment protein, ,1. In this study, we used single molecular force spectroscopy to compare the kinetics of JAM-A interactions with itself and ,1. A chimeric murine JAM-A/Fc fusion protein and the purified ,1 head domain were used to probe murine L929 cells, which express JAM-A and are susceptible to reovirus infection. The bond half-life (t1/2) of homophilic JAM-A interactions was found to be shorter () than that of ,1/JAM-A interactions (). These results are in accordance with the physiological functions of JAM-A and ,1. A short bond lifetime imparts a highly dynamic nature to homophilic JAM-A interactions for regulating tight junction permeability while stable interactions between ,1 and JAM-A likely anchor the virus to the cell surface and facilitate viral entry. Copyright © 2008 John Wiley & Sons, Ltd. [source] Severe acute respiratory syndrome coronavirus entry into host cells: Opportunities for therapeutic intervention,MEDICINAL RESEARCH REVIEWS, Issue 4 2006Kap-Sun Yeung Abstract A novel human coronavirus (CoV) has been identified as the etiological agent that caused the severe acute respiratory syndrome (SARS) outbreak in 2003. The spike (S) protein of this virus is a type I surface glycoprotein that mediates binding of the virus to the host receptor and the subsequent fusion between the viral and host membranes. Because of its critical role in viral entry, the S protein is an important target for the development of anti-SARS CoV therapeutics and prophylactics. This article reviews the structure and function of the SARS CoV S protein in the context of its role in virus entry. Topics that are discussed include: the interaction between the S1 domain of the SARS spike protein and the cellular receptor, angiotensin converting enzyme 2 (ACE2), and the structural features of the ectodomain of ACE2; the antigenic determinants presented by the S protein and the nature of neutralizing monoclonal antibodies that are elicited in vivo; the structure of the 4,3-hydrophobic heptad repeats HR1 and HR2 of the S2 domain and their interaction to form a six-helical bundle during the final stages of fusion. Opportunities for the design and development of anti-SARS agents based on the inhibition of receptor binding, the therapeutic uses of S-directed monoclonal antibodies and inhibitors of HR1,HR2 complex formation are presented. © 2006 Wiley Periodicals, Inc. Med Res Rev, 26, No. 4, 414,433, 2006 [source] Structural improvement of unliganded simian immunodeficiency virus gp120 core by normal-mode-based X-ray crystallographic refinementACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Xiaorui Chen The envelope protein gp120/gp41 of simian and human immunodeficiency viruses plays a critical role in viral entry into host cells. However, the extraordinarily high structural flexibility and heavy glycosylation of the protein have presented enormous difficulties in the pursuit of high-resolution structural investigation of some of its conformational states. An unliganded and fully glycosylated gp120 core structure was recently determined to 4.0,Å resolution. The rather low data-to-parameter ratio limited refinement efforts in the original structure determination. In this work, refinement of this gp120 core structure was carried out using a normal-mode-based refinement method that has been shown in previous studies to be effective in improving models of a supramolecular complex at 3.42,Å resolution and of a membrane protein at 3.2,Å resolution. By using only the first four nonzero lowest-frequency normal modes to construct the anisotropic thermal parameters, combined with manual adjustments and standard positional refinement using REFMAC5, the structural model of the gp120 core was significantly improved in many aspects, including substantial decreases in R factors, better fitting of several flexible regions in electron-density maps, the addition of five new sugar rings at four glycan chains and an excellent correlation of the B -factor distribution with known structural flexibility. These results further underscore the effectiveness of this normal-mode-based method in improving models of protein and nonprotein components in low-resolution X-ray structures. [source] How Oestrogen or Progesterone might Change a woman's susceptibility to HIV-1 infectionAUSTRALIAN AND NEW ZEALAND JOURNAL OF OBSTETRICS AND GYNAECOLOGY, Issue 5 2002Li Mingjia ABSTRACT Worldwide, 18.5 million women are infected with the human immunodeficiency virus (HIV-1). At least 80% of these HIV infections have occurred as a result of sexual intercourse with an infected male partner. This review focuses on how HIV-1 enters the human female reproductive tract, and how oestrogen or progesterone, by altering the cervicovaginal epithelium, might change a woman's susceptibility to HIV infection. Experiments on hysterectomised Rhesus monkeys suggest that the vagina, rather than the cervix or uterus, is the main site of viral entry. If ovariectomised monkeys are given systemic oestrogen treatment, this makes them completely resistant to infection by intravaginally administered simian immunodeficiency virus (SIV), whereas progesteronetreated animals, like the untreated controls, are extremely susceptible. Some studies have also shown that women on systemic long-acting gestagen-only contraceptives have a thinner vaginal epithelium and hence might be more susceptible to HIV infection; this is certainly true of post-menopausal women. The beneficial effects of oestrogen are thought to be due to increased thickness and cornification of the cervicovaginal epithelium, which prevents the virus from coming into contact with the target Langerhans cells (LCs). Topical vaginal oestrogen treatment is widely used as a safe and effective way of thickening and keratinising the vaginal epithelium in post-menopausal women. Perhaps this could be an exciting new way of protecting women from HIV infection. [source] A new player in a deadly game: influenza viruses and the PI3K/Akt signalling pathwayCELLULAR MICROBIOLOGY, Issue 6 2009Christina Ehrhardt Summary Upon influenza A virus infection of cells, a wide variety of antiviral and virus-supportive signalling pathways are induced. Phosphatidylinositol-3-kinase (PI3K) is a recent addition to the growing list of signalling mediators that are activated by these viruses. Several studies have addressed the role of PI3K and the downstream effector protein kinase Akt in influenza A virus-infected cells. PI3K/Akt signalling is activated by diverse mechanisms in a biphasic manner and is required for multiple functions during infection. While the kinase supports activation of the interferon regulatory factor-3 during antiviral interferon induction, it also exhibits virus supportive functions. In fact, PI3K not only regulates a very early step during viral entry but also results in suppression of premature apoptosis at later stages of infection. The latter function is dependent on the expression of the viral non-structural protein-1 (A/NS1). It has been shown that PI3K activation occurs by direct interaction of A/NS1 with the p85 regulatory subunit and interaction sites of A/NS1 and p85 have now been mapped in detail. Here, we summarize the current knowledge on influenza virus-induced PI3K signalling and how this pathway supports viral propagation. [source] Cell entry by human pathogenic arenavirusesCELLULAR MICROBIOLOGY, Issue 4 2008Jillian M. Rojek Summary The arenaviruses Lassa virus (LASV) in Africa and Machupo (MACV), Guanarito (GTOV) and Junin viruses (JUNV) in South America cause severe haemorrhagic fevers in humans with fatality rates of 15,35%. The present review focuses on the first steps of infection with human pathogenic arenaviruses, the interaction with their cellular receptor molecules and subsequent entry into the host cell. While similarities exist in genomic organization, structure and clinical disease caused by pathogenic Old World and New World arenaviruses these pathogens use different primary receptors. The Old World arenaviruses employ ,-dystroglycan, a cellular receptor for proteins of the extracellular matrix, and the human pathogenic New World arenaviruses use the cellular cargo receptor transferrin receptor 1. While the New World arenavirus JUNV enters cells via clathrin-dependent endocytosis, evidence occurred for clathrin-independent entry of the prototypic Old World arenavirus lymphocytic choriomeningitis virus. Upon internalization, arenaviruses are delivered to the endosome, where pH-dependent membrane fusion is mediated by the envelope glycoprotein (GP). While arenavirus GPs share characteristics with class I fusion GPs of other enveloped viruses, unusual mechanistic features of GP-mediated membrane fusion have recently been discovered for arenaviruses with important implications for viral entry. [source] | ||||||||||||||||