Articles by Summer Zhang in JoVE
לדמיין וירוס דנגה דרך אלקסה פלואוריד תיוג Summer Zhang1, Hwee Cheng Tan2, Eng Eong Ooi3 1Defence Medical and Environmental Research Institute, DSO National Laboratories, 2Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, 3Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School ניצול של התקדמות בפיתוח fluorophore ואת טכנולוגיית הדמיה, שיטה פשוטה של אלקסה פלואוריד תיוג של וירוס דנגה תוכננה כדי לחזות את האינטראקציות המוקדמות בין וירוס לתא.
Other articles by Summer Zhang on PubMed
A Small Molecule Fusion Inhibitor of Dengue Virus Antiviral Research. Dec, 2009 | Pubmed ID: 19800368 The dengue virus envelope protein plays an essential role in viral entry by mediating fusion between the viral and host membranes. The crystal structure of the envelope protein shows a pocket (located at a "hinge" between Domains I and II) that can be occupied by ligand n-octyl-beta-D-glucoside (betaOG). Compounds blocking the betaOG pocket are thought to interfere with conformational changes in the envelope protein that are essential for fusion. Two fusion assays were developed to examine the anti-fusion activities of compounds. The first assay measures the cellular internalization of propidium iodide upon membrane fusion. The second assay measures the protease activity of trypsin upon fusion between dengue virions and trypsin-containing liposomes. We performed an in silico virtual screening for small molecules that can potentially bind to the betaOG pocket and tested these candidate molecules in the two fusion assays. We identified one compound that inhibits dengue fusion in both assays with an IC(50) of 6.8 microM and reduces viral titers with an EC(50) of 9.8 microM. Time-of-addition experiments showed that the compound was only active when present during viral infection but not when added 1h later, in agreement with a mechanism of action through fusion inhibition.
A Simple Method for Alexa Fluor Dye Labelling of Dengue Virus Journal of Virological Methods. Aug, 2010 | Pubmed ID: 20399231 Dengue virus causes frequent and cyclical epidemics throughout the tropics, resulting in significant morbidity and mortality rates. There is neither a specific antiviral treatment nor a vaccine to prevent epidemic transmission. The lack of a detailed understanding of the pathogenesis of the disease complicates these efforts. The development of methods to probe the interaction between the virus and host cells would thus be useful. Direct fluorescence labelling of virus would facilitate the visualization of the early events in virus-cell interaction. This report describes a simple method of labelling of dengue virus with Alexa Fluor succinimidyl ester dye dissolved directly in the sodium bicarbonate buffer that yielded highly viable virus after labelling. Alexa Fluor dyes have superior photostability and are less pH-sensitive than the common dyes, such as fluorescein and rhodamine, making them ideal for studies on cellular uptake and endosomal transport of the virus. The conjugation of Alexa Fluor dye did not affect the recognition of labelled dengue virus by virus-specific antibody and its putative receptors in host cells. This method could have useful applications in virological studies.
Ligation of Fc Gamma Receptor IIB Inhibits Antibody-dependent Enhancement of Dengue Virus Infection Proceedings of the National Academy of Sciences of the United States of America. Jul, 2011 | Pubmed ID: 21746897 The interaction of antibodies, dengue virus (DENV), and monocytes can result in either immunity or enhanced virus infection. These opposing outcomes of dengue antibodies have hampered dengue vaccine development. Recent studies have shown that antibodies neutralize DENV by either preventing virus attachment to cellular receptors or inhibiting viral fusion intracellularly. However, whether the antibody blocks attachment or fusion, the resulting immune complexes are expected to be phagocytosed by Fc gamma receptor (FcÎ³R)-bearing cells and cleared from circulation. This suggests that only antibodies that are able to block fusion intracellularly would be able to neutralize DENV upon FcÎ³R-mediated uptake by monocytes whereas other antibodies would have resulted in enhancement of DENV replication. Using convalescent sera from dengue patients, we observed that neutralization of the homologous serotypes occurred despite FcÎ³R-mediated uptake. However, FcÎ³R-mediated uptake appeared to be inhibited when neutralized heterologous DENV serotypes were used instead. We demonstrate that this inhibition occurred through the formation of viral aggregates by antibodies in a concentration-dependent manner. Aggregation of viruses enabled antibodies to cross-link the inhibitory FcÎ³RIIB, which is expressed at low levels but which inhibits FcÎ³R-mediated phagocytosis and hence prevents antibody-dependent enhancement of DENV infection in monocytes.