Domain-III FG loop of the dengue virus type 2 envelope protein is important for infection of mammalian cells and Aedes aegypti mosquitoes

The FG extended loop in domain III of the dengue virus type 2 (DENV2) envelope protein is postulated to be a molecular determinant for host cell infectivity. To determine the contribution of the FG loop to virus infectivity, an infectious cDNA clone of DENV2 was manipulated by deleting amino acids in the loop (VEPGΔ) to mimic tick-borne flaviviruses or by substituting these AAs with RGD or RGDK/S to mimic motifs present in other mosquito-borne flaviviruses. We found the FG loop to be dispensable for infection of C6/36 cells but critical for infection of Aedes aegypti mosquito midguts and mammalian cells. All the FG loop mutants were able to bind to and enter mammalian cells but replication of VEPGΔ in Vero cells at 37 °C was delayed until acquisition of secondary mutations. Reduced binding of DENV2 type-specific monoclonal antibody 3H5 to mutant viruses confirmed the FG loop motif as its target epitope.     

Characterization of dengue complex-reactive epitopes on dengue 3 virus envelope protein domain III

The disease dengue (DEN) is caused by four genetically and serologically related viruses termed DENV-1, -2, -3, and -4. The DENV envelope (E) protein ectodomain can be divided into three structural domains designated ED1, ED2, and ED3. The ED3 contains the DENV type-specific and DENV complex-reactive (epitopes shared by DENV 1-4) antigenic sites. In this study the epitopes recognized by four DENV complex-reactive monoclonal antibodies (MAbs) with neutralizing activity were mapped on the DENV-3 ED3 using a combination of physical and biological techniques. Amino acid residues L306, K308, G381, I387, and W389 were critical for all four MAbs, with residues V305, E309, V310, K325, D382, A384, K386, and R391 being critical for various subsets of the MAbs. A previous study by our group (Gromowski, G.D., Barrett, N.D., Barrett, A.D., 2008. Characterization of dengue complex-specific neutralizing epitopes on the envelope protein domain III of dengue 2 virus. J. Virol 82, 8828-8837) characterized the same panel of MAbs with DENV-2. The location of the DENV complex-reactive antigenic site on the DENV-2 and DENV-3 ED3s is similar; however, the critical residues for binding are not identical. Overall, this indicates that the DENV complex-reactive antigenic site on ED3 may be similar in location, but the surprising result is that DENV 2 and 3 exhibit unique sets of residues defining the energetics of interaction to the same panel of MAbs. These results imply that the amino acid sequences of DENV define a unique interaction network among these residues in spite of the fact that all flavivirus ED3s to date assume the same structural fold.     

Solution structure of the envelope protein domain III of dengue-4 virus

The disease dengue (DEN) is caused by four serologically related viruses termed DEN1, DEN2, DEN3 and DEN4. The structure of the ectodomain of the envelope protein has been determined previously for DEN2 and DEN3 viruses. Using NMR spectroscopic methods, we solved the solution structure of domain III (ED3), the receptor-binding domain, of the envelope protein of DEN4 virus, human strain 703-4. The structure shows that the nine amino acid changes in ED3 that separate the sylvatic and human DEN4 strains are surface exposed. Important structural differences between DEN4-rED3 and ED3 domains of DEN2, DEN3 and other flaviviruses are discussed.     

C6/36细胞感染登革Ⅱ型病毒前后差异表达蛋白的初步鉴定

目的 了解C6/36细胞感染登革病毒前后相关表达蛋白的变化情况。方法 分别提取C6/36细胞和登革Ⅱ型病毒感染后的C6/36细胞的可溶性蛋白质,SDS-PAGE凝胶电泳对比分析C6/36细胞感染登革病毒前后电泳图谱的差异;分别以正常C6/36细胞总蛋白质、C6/36细胞感染登革病毒后的SDS-PAGE凝胶图谱中的差异条带蛋白免疫Balb/c小鼠的免疫血清、Santa-Cruz公司登革病毒单抗作一抗,Western-blot鉴定C6/36细胞感染登革病毒前后SDS-PAGE凝胶电泳图中的差异条带。结果 SDS-PAGE凝胶电泳图显示约40 000 Mr和70 000 Mr处,C6/36细胞感染登革病毒后的蛋白条带比正常C6/36细胞的蛋白条带明显粗亮;Western-blot鉴定确认差异条带不是登革病毒在细胞表达的蛋白质,而是C6/36细胞本身表达的蛋白质。感染前后的40 000 Mr和70 000 Mr蛋白条带同源。结论 C6/36细胞感染登革病毒前后分子量为40 000 Mr和70 000 Mr蛋白表达有差异。     

Promotion of retroviral entry in the absence of envelope protein by chlorpromazine

Retrovirus packaging cell lines that express the Moloney murine leukemia virus gag, pol, and env genes and a retroviral vector genome can produce virus particles that are capable of transducing cells. Normally if the packaging cell line does not produce a functional viral fusion glycoprotein, such as the retroviral envelope protein or a foreign viral glycoprotein, then the viruses will be incapable of transducing cells. We have found that incubating envelope protein-deficient virus particles bound to cells with chlorpromazine leads to transduction. Chlorpromazine (CPZ) is a membrane-active reagent that is commonly used to induce the hemifusion to fusion transition when membrane fusion is mediated by partially defective viral glycoproteins. The concentration and pH dependence of the promotion of transduction by CPZ is consistent with a role for CPZ micelle formation in viral entry. These data indicate that caution is warranted when experiments concerning membrane fusion completion promoted by CPZ are analyzed.