Herpes simplex virus glycoproteins gB and gH function in fusion between the virion envelope and the outer nuclear membrane

Herpesviruses must traverse the nuclear envelope to gain access to the cytoplasm and, ultimately, to exit cells. It is believed that herpesvirus nucleocapsids enter the perinuclear space by budding through the inner nuclear membrane (NM). To reach the cytoplasm these enveloped particles must fuse with the outer NM and the unenveloped capsids then acquire a second envelope in the trans-Golgi network. Little is known about the process by which herpesviruses virions fuse with the outer NM. Here we show that a herpes simplex virus (HSV) mutant lacking both the two putative fusion glycoproteins gB and gH failed to cross the nuclear envelope. Enveloped virions accumulated in the perinuclear space or in membrane vesicles that bulged into the nucleoplasm (herniations). By contrast, mutants lacking just gB or gH showed only minor or no defects in nuclear egress. We concluded that either HSV gB or gH can promote fusion between the virion envelope and the outer NM. It is noteworthy that fusion associated with HSV entry requires the cooperative action of both gB and gH, suggesting that the two types of fusion (egress versus entry) are dissimilar processes.     

Myelin-associated glycoprotein mediates membrane fusion and entry of neurotropic herpesviruses

Varicella-zoster virus (VZV) and herpes simplex virus (HSV) are prevalent neurotropic herpesviruses that cause various nervous system diseases. Similar to other enveloped viruses, membrane fusion is an essential process for viral entry. Therefore, identification of host molecules that mediate membrane fusion is important to understand the mechanism of viral infection. Here, we demonstrate that myelin-associated glycoprotein (MAG), mainly distributed in neural tissues, associates with VZV glycoprotein B (gB) and promotes cell-cell fusion when coexpressed with VZV gB and gH/gL. VZV preferentially infected MAG-transfected oligodendroglial cells. MAG also associated with HSV-1 gB and enhanced HSV-1 infection of promyelocytes. These findings suggested that MAG is involved in VZV and HSV infection of neural tissues.     

An adenovirus recombinant that expresses the human cytomegalovirus major envelope glycoprotein and induces neutralizing antibodies

The gene of the human cytomegalovirus (HCMV) major envelope glycoprotein, gB, was cloned from the Towne strain and inserted into adenovirus type 5 downstream of the E3 promoter. The recombinant virus, Ad-gB, expressed antigenically related proteins of 58, 30, 25, and 23 kDa in A549 and MRC-5 cells; the 58-kDa protein had the same mobility as the native gB from HCMV-infected MRC-5 cells and virions. All four proteins were detected by a monospecific polyclonal antiserum and by a monoclonal antibody in immunoblot and immunofluorescence assays. Hamsters infected intranasally with live Ad-gB developed protein-specific and HCMV-neutralizing antibody. This study confirms the importance of gB in the generation of the neutralizing immune response to HCMV and demonstrates the potential of live adenoviruses as vaccine vectors.     

Analysis of HIV-1 envelope mutants and pseudotyping of replication-defective HIV-1 vectors by genetic complementation.

Infectious HIV-1 particles containing replication-defective vectors that express the hygromycin B phosphotransferase gene were generated by transient complementation in COS-1 cells. A defective vector dependent only on trans-complementation with an env gene and a small vector containing a deletion of almost all of the trans region were used to examine pseudotyping of HIV-1 by an amphotropic murine retrovirus. Although pseudotyping by the heterologous envelope glycoprotein occurred with efficiency, no pseudotyping at the RNA level was observed. Genetic complementation was used to rapidly analyze the effect of env mutations in the V3, proteolytic processing site, fusion domain, and cytoplasmic tail on viral infectivity. Mutations decreasing syncytium formation usually also lowered infectivity. However, a mutation in the cytoplasmic tail and a separate mutation adjacent to the fusion domain dramatically decreased viral particle infectivity but did not appreciably decrease envelope glycoprotein-mediated cell-to-cell fusion. These results may indicate that these regions of the transmembrane peptide are necessary for acquisition of envelope glycoprotein by budding virus particles or for virus entry.     

Expression of herpes simplex virus 1 glycoprotein B by a recombinant vaccinia virus and protection of mice against lethal herpes simplex virus 1 infection.

The herpes simplex virus 1 (HSV-1) strain F gene encoding glycoprotein gB was isolated and modified at the 5' end by in vitro oligonucleotide-directed mutagenesis. The modified gB gene was inserted into the vaccinia virus genome and expressed under the control of a vaccinia virus promoter. The mature gB glycoprotein produced by the vaccinia virus recombinant was glycosylated, was expressed at the cell surface, and was indistinguishable from authentic HSV-1 gB in terms of electrophoretic mobility. Mice immunized intradermally with the recombinant vaccinia virus produced gB-specific neutralizing antibodies and were resistant to a lethal HSV-1 challenge.     

Stimulation of glycoprotein gp120 dissociation from the envelope glycoprotein complex of human immunodeficiency virus type 1 by soluble CD4 and CD4 peptide derivatives: implications for the role of the complementarity-determining region 3-like region in membrane fusion.

We have used a recombinant vaccinia virus vector encoding the envelope glycoprotein of human immunodeficiency virus type 1 to study receptor-induced structural changes related to membrane fusion. A truncated soluble form of human CD4 (sCD4) was found to stimulate dissociation of the external subunit (gp120) from the envelope glycoprotein complex of human immunodeficiency virus type 1 expressed at the cell surface. sCD4 stimulation of gp120 release was time- and concentration-dependent and was associated with specific binding of sCD4 to gp120. Synthetic peptide derivatives corresponding to residues 81-92 of human CD4 (overlapping the complementarity-determining region 3-like region) inhibited cell-cell fusion mediated by the interaction between recombinant vaccinia-encoded CD4 and human immunodeficiency virus envelope glycoprotein. These peptide derivatives also stimulated gp120 release from the envelope glycoprotein complex. An analogous peptide derivative from chimpanzee CD4 (containing a single Glu----Gly substitution at the position corresponding to CD4 residue 87) was considerably less active at inhibition of cell-cell fusion and stimulation of gp120 release, consistent with the known inhibitory effect of this substitution on the ability of membrane-associated CD4 to mediate cell fusion. These results suggest that the sCD4-induced release of gp120 reflects postbinding structural changes in the envelope glycoprotein complex involved in membrane fusion, with the complementarity-determining region 3-like region playing a critical role.     

日本血吸虫脂肪酸结合蛋白基因在家蚕细胞及幼虫中的表达

目的： 在家蚕细胞和幼虫中表达日本血吸虫脂肪酸结合蛋白（ Ｓｊ１４） 基因。方法： 将该基因克隆于昆虫病毒转移载体ｐ Ｂａｃ Ｐ Ａ Ｋ Ｈｉｓ１ 中, 再与修饰的家蚕核型多角体病毒（ Ｂｍ Ｎ Ｐ Ｖ） 线性化 Ｄ Ｎ Ａ 共转染家蚕细胞,经体内重组得重组病毒 Ｂｍ Ｓｊ１４ , 再将 Ｂｍ Ｓｊ１４ 感染家蚕细胞和幼虫以表达 Ｓｊ１４ , 用 Ｗｅｓｔｅｒｎ ｂｌｏｔ 和间接 Ｅ Ｌ Ｉ Ｓ Ａ测定表达产物的抗原性。结果： Ｂｍ Ｓｊ１４ 感染家蚕细胞和幼虫后 Ｓｊ１４ 获得较高表达; 表达产物ｒ Ｓｊ１４ （ Ｈｉｓ） 为１８ｋ Ｄａ 的融合蛋白, 在家蚕细胞中的产量约为１００ μｇ／１ ×１０６ 细胞, 在培养上清中产量为３３ μｇ／ｍｌ; 在家蚕血淋巴中得量为４ ｍｇ／ｍｌ; 在家蚕幼虫组织的得量为４６ ｍｇ／ｇ 组织。 Ｗｅｓｔｅｒｎ ｂｌｏｔ 和间接 Ｅ Ｌ Ｉ Ｓ Ａ 显示ｒ Ｓｊ１４ （ Ｈｉｓ） 具有较高抗原性。结论： Ｓｊ１４ 在家蚕细胞和幼虫中获得高效表达且表达产物具有较高抗原性。     

Use of herpes simplex virus and pseudorabies virus chimeric glycoprotein D molecules to identify regions critical for membrane fusion

Membrane fusion induced by herpes simplex virus (HSV) requires the action of four viral membrane glycoproteins (gB, gD, gH, and gL) and the binding of gD to one of its receptors, such as the herpesvirus entry mediator or nectin-1. The related animal herpesvirus, pseudorabies virus (PRV), encodes a homologous set of glycoproteins and its gD can also use nectin-1 as an entry receptor. We show here that PRV gD, when coexpressed with HSV gB, gH, and gL, cannot substitute for HSV gD in inducing fusion with target cells expressing nectin-1. Chimeric gD molecules composed of HSV and PRV sequences can substitute, provided the first 285 aa are from HSV gD. Because the first 261 aa were sufficient for receptor binding, this suggested that amino acids 262-285 contain a region required for cell fusion but not for receptor binding. Deletions from amino acids 250-299 failed to identify a specific subregion critical for cell fusion, except possibly for amino acids 250-255, which also influenced receptor binding. Instead, presence of a flexible stalk between the membrane and receptor-binding domain appears to be required, perhaps to enable conformational changes in gD on receptor binding and subsequent interactions of undefined regions of gD with the other glycoproteins required for membrane fusion.     

The soluble ectodomain of herpes simplex virus gD contains a membrane-proximal pro-fusion domain and suffices to mediate virus entry

Entry of herpes simplex virus (HSV) 1 into cells requires the interaction of HSV gD with herpesvirus entry mediator or nectin1 receptors, and fusion with cell membrane mediated by the fusion glycoproteins gB, gH, and gL. We report that the gD ectodomain in soluble form (amino acids 1-305) was sufficient to rescue the infectivity of a gD-null HSV mutant, indicating that gD does not need to be anchored to the virion envelope to mediate entry. Entry mediated by soluble gD required, in addition to the receptor-binding sites contained within residues 1-250, a discrete downstream portion (amino acids 261-305), located proximal to the transmembrane segment in full-length gD. We named it as profusion domain. The pro-fusion domain was required for entry mediated by virion-bound gD, because its substitution with the corresponding region of CD8 failed to complement the infectivity of gD(-/+) HSV. Furthermore, a receptor-negative gD (gD(Delta6-259)) inhibited virus infectivity when coexpressed with wild-type gD; i.e., it acted as a dominant-negative gD mutant. The pro-fusion domain is proline-rich, which is characteristic of regions involved in protein-protein interactions. P291L-P292A substitutions diminished the gD capacity to complement gD(-/+) HSV infectivity. We propose that gD forms a tripartite complex with its receptor and, by way of the proline-rich pro-fusion domain, with the fusion glycoproteins, or with one of them. The tripartite complex would serve to recruit/activate the fusion glycoproteins and bring them from a fusion-inactive to a fusion-active state, such that they execute fusion of the virion envelope with cell membrane.     

猴B病毒gB基因在昆虫细胞中的表达

为了研发猴B病毒ELISA检测试剂盒中替代全病毒的抗原。根据已报道的猴B病毒E2490株gB蛋白基因序列（genbank登录号：AF533768）人工合成gB基因,通过XbaⅠ和EcoRⅠ特异性酶切,将gB基因克隆于昆虫杆状病毒表达载体pFastBacHTA,经PCR、酶切、测序鉴定后,成功构建了携带gB基因的重组质粒pFastBacHTA-gB。该重组质粒转化含有杆状病毒穿梭载体的DH10BAC感受态细胞,经抗生素、PCR筛选,获得转座的杆粒Bacmid-gB。在脂质体介导下转染sf9昆虫细胞,细胞变大变圆细胞核扩大,收获重组杆状病毒,再感染细胞,收获目的蛋白。通过SDS-PAGE和Western bloting及间接免疫荧光检测,结果表明该蛋白得到表达,且具有良好的生物活性,大小约为98kDa。实验结果表明已成功构建了携带目的基因的重组质粒pFastBacHTA-gB和转座的杆粒Bacmid-gB,转染后在sf9昆虫细胞上得到表达。此研究结果为下一步以表达的gB蛋白为诊断抗原,替代现阶段以病毒作为抗原的猴B病毒ELISA检测试剂盒的研制奠定了基础。     

汉滩病毒核蛋白部分片段与囊膜糖蛋白G1在昆虫细胞中的融合表达

目的　应用Bac -to -Bac杆状病毒表达系统融合表达汉滩病毒囊膜糖蛋白G1与核蛋白部分片段。方法　构建含有汉滩病毒G1S0 7嵌合基因的杆状病毒表达载体 pFBD -G1S0 7,转化DH10Bac致敏菌 ,利用其含有的细菌Tn7转座系统将嵌合基因重组至穿梭质粒Bacmid上 ,快速筛选出含有G1S0 7嵌合基因的重组杆状病毒 ,在昆虫细胞中表达该融合蛋白 ,利用间接免疫荧光、ELISA和免疫印迹对表达产物进行检测。结果　构建的含G1S0 7嵌合基因之重组杆状病毒可在昆虫细胞中表达出融合蛋白 ,该蛋白可被抗汉滩病毒核蛋白及糖蛋白G1特异性单抗所识别 ,表达产物主要集中在细胞内。结论　在昆虫细胞中表达出具有生物学活性的G1S0 7融合蛋白 ,为进一步研究其免疫学特性奠定了基础     

Two Sides to Every Story: Herpes Simplex Type-1 Viral Glycoproteins gB,gD, gH/gL,gK, and Cellular Receptors Function as Key Players in Membrane Fusion

Herpes simplex virus type-1 (HSV-1) and type-2 (HSV-2) are prototypical alphaherpesviruses that are characterized by their unique properties to infect trigeminal and dorsal root ganglionic neurons, respectively, and establish life-long latent infections. These viruses initially infect mucosal epithelial tissues and subsequently spread to neurons. They are associated with a significant disease spectrum, including orofacial and ocular infections for HSV-1 and genital and neonatal infections for HSV-2. Viral glycoproteins within the virion envelope bind to specific cellular receptors to mediate virus entry into cells. This is achieved by the fusion of the viral envelope with the plasma membrane. Similarly, viral glycoproteins expressed on cell surfaces mediate cell-to-cell fusion and facilitate virus spread. An interactive complex of viral glycoproteins gB, gD/gH/gL, and gK and other proteins mediate these membrane fusion phenomena with glycoprotein B (gB), the principal membrane fusogen. The requirement for the virion to enter neuronal axons suggests that the heterodimeric protein complex of gK and membrane protein UL20, found only in alphaherpesviruses, constitute a critical determinant for neuronal entry. This hypothesis was substantiated by the observation that a small deletion in the amino terminus of gK prevents entry into neuronal axons while allowing entry into other cells via endocytosis. Cellular receptors and receptor-mediated signaling synergize with the viral membrane fusion machinery to facilitate virus entry and intercellular spread. Unraveling the underlying interactions among viral glycoproteins, envelope proteins, and cellular receptors will provide new innovative approaches for antiviral therapy against herpesviruses and other neurotropic viruses.     

The herpesvirus glycoproteins B and H.L are sequentially recruited to the receptor-bound gD to effect membrane fusion at virus entry

Four glycoproteins (gD, gB, gH, and gL) are required for herpes simplex virus entry into the cell or for cell-cell fusion in transfected cells. gD serves as the receptor-binding glycoprotein and as the trigger of fusion; the other three execute fusion between the viral envelope and the plasma and endocytic membranes or the membranes of adjacent cells and are highly conserved among members of the herpesvirus family. Details of the interaction of gD with gB, gH, and gL were not known. Here, we report that the four glycoproteins assemble into a complex initiated by the interaction of gD with its cellular receptor. gB is recruited to the gD-receptor complex next, even in the absence of gH.gL. gH.gL is recruited next, but only to the receptor-gD-gB ensemble. A complex with the composition receptor-gD-gB-gH.gL is assembled transiently with a life span of 15-30 min in cells exposed to virus but can also be found in infected cells and in cells committed to form polykaryocytes after transfection of the glycoprotein quartet. The results indicate that the complex assembly is a critical step in the process of virus entry and fusion, and that no viral protein other than those that participate in the complex itself is required for complex assembly. These findings imply critical protein-protein interactions among the quartet as herpes simplex virions enter the cells and at cell-cell fusion, define a specific order of recruitment, and place gH.gL as the last link in the process of glycoprotein recruitment to the complex.     

Chemically induced mutagenesis in a shuttle vector with a low-background mutant frequency.

We have developed a recombinant DNA shuttle vector that permits the molecular analysis of mutations induced in human cells by chemical or physical mutagens. The vector is able to replicate as a plasmid in Escherichia coli and in Epstein-Barr virus (EBV)-transformed human lymphoblastoid cell lines and contains the herpes simplex virus type 1 thymidine kinase gene (HSV tk) as the target for mutagenesis studies. After introduction of the vector into an EBV-transformed lymphoblastoid cell line (LCL-721) by electroporation, approximately equal to 2% of the transfected cells expressed the vector-encoded gene for hygromycin resistance. Plasmid DNA isolated from cells immediately after selection for hygromycin resistance (10 population doublings posttransfection) contained mutations in the HSV tk gene at a frequency of 6 X 10(-5). Treatment of plasmid-bearing LCL-721 cells with N-ethyl-N-nitrosourea resulted in a dose-dependent increase of up to 15-fold in the frequency of mutations in the HSV tk gene. The dose-response for the induction of mutations in the plasmid-encoded gene closely paralleled that for the induction of mutations in the cellular gene for hypoxanthine (guanine) phosphoribosyltransferase.     

Cell fusion induced by herpes simplex virus is promoted and suppressed by different viral glycoproteins.

Some of the factors that regulate membrane fusion resulting in polykaryocyte formationhave been investigated, using the model system of human cells infected with mutants of herpes simplex virus (HSV). One of the mutant viruses used in this study (MP) failed to produce the viral glycoprotein designated C2--a nonlethal defect that has previously been correlated with the polykaryocyte-inducing phenotype of this and other mutant strains (wild-type strains of HSV usually induce the aggregation of infected cells rather than their fusion). The other mutant virus (tsB5), a temperature-sensitive conditional-lethal mutant, failed to produce glycoprotein B2 at non-permissive temperature, whereas the synthesis of all other viral products appeared to be normal. We produced and isolated seven recombinants of MP and tsB5 that expressed both of the parental alterations in glycoprotein synthesis. All of the re-combinant viruses induced the fusion of infected cells at 34 degrees (correlated with the absence of C2 expression) but were unable to cause cell fusion at 39 degrees (correlated with the absence of C2 and of B2 expression), even after infection at multiplicities high enough to ensure that all cells in the cultures synthesized viral macromolecules. These results and studies on the dominance or recessiveness of the fusion-inducing phenotype in mixed infections provide evidence that glycoprotein B2 plays a critical role in the promotion of cell fusion and that glycoprotein C2 can act to suppress fusion.     

4种血清型登革病毒多表位重组抗原的表达及血清学初步评价

目的在原核表达系统中对登革病毒包膜蛋白(E蛋白)和非结构蛋白1(NS1)融合的B细胞抗原表位进行表达、纯化及血清学评价。方法将B细胞抗原表位用形成α螺旋的连接肽(EAAAK)2作为接头,串联合成1条全新的多表位融合重组基因rE,将其克隆到原核表达载体pET-28a(+)中,转化大肠杆菌BL21(DE3)后经IPTG诱导表达融合蛋白,用镍柱对重组蛋白纯化,并用SDS-PAGE和Western blot方法鉴定表达产物。以融合蛋白为抗原,用间接ELISA检测登革热病人血清IgM抗体。结果重组表达载体pET28a-rE构建成功,并在大肠杆菌BL21(DE3)中成功表达。融合蛋白主要以包涵体形式存在,用镍柱纯化获得高纯度的目的蛋白,SDS-PAGE和Western blot检测结果显示蛋白分子量大小与预期结果相符,建立的间接ELISA具有较高的准确性。结论原核表达的登革病毒多表位融合蛋白具有良好的血清学检测价值。     

人TAT-PDX-1融合蛋白在大肠杆菌中的表达与纯化

目的构建人TAT-PDX-1表达载体,并对其融合蛋白进行纯化。方法采用RT-PCR技术从人胰腺组织中获得目的基因hPDX-1,将TAT序列与PDX-1克隆到原核表达载体pET-28a;用IPTG诱导、表达融合蛋白;NiNTAagaros纯化融合蛋白,Western blot鉴定。结果目的片段PDX-1被有效扩增,DNA序列测定表明所构建重组质粒pET28a-TAT-h PDX-1与设计相同;TAT-PDX-1融合蛋白在大肠杆菌中获得高效表达并成功纯化。结论成功地获得了TAT-hPDX-1融合基因的表达产物,为进一步研究及临床应用奠定了基础。     

狂犬病病毒G基因的克隆表达及间接ELISA检测方法的初步建立与应用

目的以重组G蛋白为检测抗原,应用间接ELISA方法检测狂犬病病毒抗体。方法根据GenBank 公布的狂犬病病毒LEP Flury株基因序列设计引物,PCR扩增出目的基因,连接pGM T载体,重组质粒经BamH I和XhoⅠ双酶切,连接到表达载体pGEX 6P 1,构建重组表达载体pGEX G。将重组表达载体转化大肠杆菌BL21(DE3)感受态细胞中,在IPTG诱导下表达目的蛋白,表达蛋白纯化后SDS PAGE电泳分析并经Western blotting鉴定。纯化的G蛋白作为包被抗原,建立间接ELISA方法检测93份犬血清抗体。结果成功构建了克隆载体pGM G和表达载体pGEX G,高效表达了狂犬病病毒G蛋白,融合蛋白分子量大小为79kDa,表达蛋白可与狂犬病病毒抗血清发生特异性反应。建立的检测方法灵敏度达到1∶1 600,与商品化的试剂盒相比符合率为96.8%。结论成功表达狂犬病病毒G蛋白,表达产物可作为检测抗原用于间接ELISA方法中狂犬病病毒抗体的检测。     

Coexpression of human immunodeficiency virus envelope proteins and tat from a single simian virus 40 late replacement vector.

A Sal I-Xho I fragment containing the genes encoding tat, art, and the envelope proteins from the BH10 clone of human immunodeficiency virus (HIV) was inserted into a simian virus 40 (SV40)-based eukaryotic expression vector. The vector is a shuttle vector that replicates to high copy numbers in both Escherichia coli and eukaryotic cells permissive for SV40 replication. Transfection of the HIV DNA-containing vector (pSVSX1) into the CV-1 monkey cell line gave high levels of expression of the envelope glycoproteins gp160 and gp120 in 20-30% of the transfected cells. By several criteria, the proteins were indistinguishable from those produced during infection. The proteins were localized to the cytoplasm and plasma membrane, and some of the gp120 was shed into the culture medium. Approximately 0.5 microgram of envelope protein could be extracted from 10(6) cells. This is at least 100 times higher than the levels found in HIV-infected H9 cells. In addition, a trans-activation assay performed with pSVSX1 and a plasmid containing the gene for chloramphenicol acetyltransferase under the control of the HIV long terminal repeat demonstrated that a functional tat gene product also was expressed. Thus, this transient vector system provides an abundant source of native envelope protein for purification and characterization and also will be useful for studies dealing with the regulation of HIV gene expression.     

Isolation and Identification of Feline Herpesvirus Type 1 from a South China Tiger in China

In 2012, an FHV-1-like virus was isolated from a tiger that presented with clinical signs of sialorrhea, sneezing and purulent rhinorrhea. Isolation was performed with the FK81 cell line, and the virus was identified by PCR, transmission electron microscopy (TEM), and the phylogenetic analysis of the partial thymidine kinase (TK) and glycoprotein B (gB) genes. A total of 253 bp of the TK gene and 566 bp of the gB gene were amplified from the trachea of the tiger by PCR/RT-PCR method. Phylogenetic analysis showed that the isolate belonged to the same cluster with other FHV-1 strains obtained from GenBank. Herpes-like viruses with an envelope and diameters of approximately 200 nm were observed in the culture supernatants of FK81 cells inoculated with samples from the tiger. The FHV-1 infection was confirmed by an animal challenge experiment in a cat model. Our finding extends the host range of FHV-1 and has implications for FHV-1 infection and South China tiger conservation.