Intracellular localization and DNA-binding properties of human papillomavirus type 18 E6 protein expressed with a baculovirus vector.

The E6 protein of human papillomavirus type 18 (HPV-18) is a putative zinc-finger protein that is expressed in HPV-18-induced genital neoplasias. We have studied the biochemical properties of E6 protein synthesized in large amounts with a baculovirus expression vector. When E6 protein was synthesized in insect cells infected with an E6-expressing baculovirus, the protein was localized to both nuclear and membrane fractions, with half-lives of 4 and 2 h, respectively. Changing the first five amino acids of E6 did not alter the pattern of cellular localization of the protein but dramatically increased the half-life of the nuclear component to longer than 30 h and increased the half-life of the membrane component to 8 h. Although the baculovirus-expressed E6 protein bound to double-stranded DNA with high affinity, no sequence specificity for HPV-18 DNA was detected.     

High-Yield Expression in Escherichia coli and Purification of Mouse Ubiquitin-Activating Enzyme E1

Research in the ubiquitin field requires large amounts of ubiquitin-activating enzyme (E1) for in vitro ubiquitination assays. Typically, the mammalian enzyme is either isolated from natural sources or produced recombinantly using baculovirus/insect cell protein expression systems. Escherichia coli is seldom used to produce mammalian E1 probably due to the instability and insolubility of this high-molecular mass protein. In this report, we show that 5-10 mg of histidine-tagged mouse E1 can be easily obtained from a 1 l E. coli culture. A low temperature during the protein induction step was found to be critical to obtain an active enzyme.     

A novel 40-kDa protein containing six repeats of an epidermal growth factor-like domain functions as a pattern recognition protein for lipopolysaccharide

Determination of structures and functions of pattern recognition proteins are important for understanding pathogen recognition mechanisms in host defense and for elucidating the activation mechanism of innate immune reactions. In this study, a novel 40-kDa protein, named LPS recognition protein (LRP), was purified to homogeneity from the cell-free plasma of larvae of the large beetle, Holotrichia diomphalia. LRP exhibited agglutinating activities on Escherichia coli, but not on Staphylococcus aureus and Candida albicans. This E. coli-agglutinating activity was preferentially inhibited by the rough-type LPS with a complete core oligosaccharide. LRP consists of 317 aa residues and six repeats of an epidermal growth factor-like domain. Recombinant LRP expressed in a baculovirus system also showed E. coli agglutination activity in vitro and was able to neutralize LPS by inhibition of LPS-induced IL-6 production in mouse bone marrow mast cells. Furthermore, E. coli coated with the purified LRP were more rapidly cleared in the Holotrichia larvae than only E. coli, indicating that this protein participates in the clearance of E. coli in vivo. The three amino-terminal epidermal growth factor-like domains of LRP, but not the three carboxyl epidermal growth factor-like domains, are involved in the LPS-binding activity. Taken together, this LRP functions as a pattern recognition protein for LPS and plays a role as an innate immune protein.     

Plasmid RSF1010 DNA replication in vitro promoted by purified RSF1010 RepA, RepB and RepC proteins.

We have constructed and analyzed an in vitro system that will efficiently replicate plasmid RSF1010 and its derivatives. The system contains a partially purified extract from E.coli cells and three purified RSF1010-encoded proteins, the products of genes repA, repB (or mobA/repB), and repC. Replication in this system mimics the in vivo mechanism in that it (i) is initiated at oriV, the origin of vegetative DNA replication, (ii) proceeds in a population of plasmid molecules in both directions from this 396-base-pair origin region, and (iii) is absolutely dependent on the presence of each of the three rep gene products. In addition, we find that E.coli DNA gyrase, DnaZ protein (gamma subunit of poIIII holoenzyme) and SSB are required for in vitro plasmid synthesis. The bacterial RNA polymerase, the initiation protein DnaA, and the primosomal proteins DnaB, DnaC, DnaG and DnaT are not required. Furthermore, the replicative intermediates seen in the electron microscope suggest that replication in vitro begins with the simultaneous or non-simultaneous formation of two displacement loops that expand for a short stretch of DNA toward each other, and form a theta-type structure when the two displacing strands pass each other.     

RGD motifs on the surface of baculovirus enhance transduction of human lung carcinoma cells

Baculovirus vectors have been shown to enter a variety of mammalian cell lines and gene transfer with wild-type baculovirus (WT) has been demonstrated both in vitro and in vivo. Different protein motifs have been displayed on the viral surface to serve as ligands for cell-specific receptor molecules. We have generated recombinant baculovirus vectors displaying an RGD-motif, recognized by alphaV integrin, on the viral surface. The RGD motifs within the C-terminus of coxsackie virus A9 and human parechovirus 1 VP1 proteins were fused to the N-terminus of the major envelope glycoprotein, gp64, of Autographa californica multiple nucleopolyhedrovirus. The recombinant RGD-presenting viruses bound more efficiently to the surface of human lung carcinoma cells (A549), known to contain alphaV integrins, as compared to WT baculovirus. In addition, the binding pattern of the RGD-displaying baculovirus showed extensive clustering. This most likely represents clustering of the integrin molecules on the cell surface, induced by binding of the RGD-displaying baculovirus. Finally, the transduction efficiency of an RGD-representing virus increased by almost three-fold as monitored by light emission measurements. In conclusion, these results suggest that the RGD-motif is functional on the surface of baculovirus and thereby these tropism-modified viruses bind more efficiently as well as enhance the transduction efficiency of human cancer cells expressing alphaV integrins.     

人乳头瘤病毒16型E6基因的T—A克隆及在真核细胞中的表达

由于ＨＰＶ１６Ｅ６蛋白能诱导机体保护性免疫反应,可作为基因治疗的靶抗原。用杆状病毒昆虫细胞表达系统制备了ＨＰＶ１６Ｅ６基因工程蛋白,拟用于宫颈癌细胞系小鼠模型抗癌的免疫治疗。用ＰＣＲ技术从ＨＰＶ１６基因组中扩增获得转化基因Ｅ６的完整ＯＲＦ,按ＴＡ策略将其克隆到自行制备的杆状病毒转移载体ｐＶＬ１３９３Ｔ尾载体中,置于杆状病毒ＡｃＭＮＰＶＰｏｌｈ晚期启动子控制之下,用此重组转移质粒ｐＶＬ１３９３Ｅ６与杆状病毒ＤＮＡ共转染昆虫细胞Ｓｆ９,经噬斑筛选获得带有编码Ｅ６蛋白基因的重组杆状病毒株,并在昆虫细胞Ｓｆ９中表达为非融合性Ｅ６蛋白。ＳＤＳＰＡＧＥ电泳分析其分子量约为１８ｋＤ,免疫印迹实验表明,此重组蛋白能被兔抗ＨＰＶ１６Ｅ６抗体所识别。     

丙型肝炎病毒结构蛋白E1在昆虫细胞中的表达及定位

本文在大肠杆菌中表达了与GST融合无跨膜区的丙型肝炎病毒(Hepatitis C Virus,HCV)E1蛋白,并通过免疫兔制备了兔抗E1的抗血清。然后利用Bac-to-Bac杆状病毒表达系统构建了含有HCV结构蛋白E1基因的重组杆状病毒vAcHCVE1。通过Western blot分析,E1蛋白在Sf9细胞中表达分子量大小为30kDa大于预测的20kDa,表明存在翻译后修饰如糖基化等。通过Confocal显微镜观察当感染48h后E1蛋白定位在细胞质和细胞膜上。     

人视黄醇结合蛋白4在杆状病毒系统中的表达及其多克隆抗体制备

旨在利用杆状病毒系统表达、制备人视黄醇结合蛋白(RBP4)并检测其免疫原性。将人RBP4基因片段及信号肽SS64片段亚克隆到杆状病毒转移载体pFastBac-dual(pFBd)中,获得相应的重组转移质粒;转化大肠杆菌菌株DH10bac,转座后经筛选获得重组穿梭质粒rbacmid,将重组穿梭质粒转染孔板培养的Sf9细胞,获得含人RBP4表达框的重组杆状病毒,经过扩增获得毒种。毒种感染对数生长期的Sf9细胞并表达人RBP4蛋白(I-RBP4),通过SDS-PAGE和Western blotting对表达蛋白进行检测和鉴定。用毒种感染悬浮培养的Sf9细胞制备一批RBP4蛋白,完成SDS、Western blotting的检测及少量的多抗制备。纯化重组蛋白并与E.coli重组人RBP4(E-RBP4)分别免疫家兔。实验结果,酶切鉴定及测序证实重组转移质粒构建正确;成功构建重组RBP4-bacmid;人RBP4蛋白在昆虫细胞获得高效表达。表达的RBP4蛋白可以分泌到培养基中,分子量约为23 kDa,经过计算表达量为100 mg/L;纯化蛋白免疫兔子制备了多抗血清,血清滴度为1∶100 000,高于原核表达的抗体滴度(1∶10 000),与人体提纯蛋白制备的抗体滴度相近。杆状病毒系统高效表达了人的RBP4蛋白,具有较好的抗原性,并获得高亲和力的抗血清,为下一步的人血RBP4检测试剂盒的制备打下了坚实的基础。     

The human coronavirus 229E superfamily 1 helicase has RNA and DNA duplex-unwinding activities with 5'-to-3' polarity

The human coronavirus 229E replicase gene encodes a protein, p66HEL, that contains a putative zinc finger structure linked to a putative superfamily (SF) 1 helicase. A histidine-tagged form of this protein, HEL, was expressed using baculovirus vectors in insect cells. The purified recombinant protein had in vitro ATPase activity that was strongly stimulated by poly(U), poly(dT), poly(C), and poly(dA), but not by poly(G). The recombinant protein also had both RNA and DNA duplex-unwinding activities with 5'-to-3' polarity. The DNA helicase activity of the enzyme preferentially unwound 5'-oligopyrimidine-tailed, partial-duplex substrates and required a tail length of at least 10 nucleotides for effective unwinding. The combined data suggest that the coronaviral SF1 helicase functionally differs from the previously characterized RNA virus SF2 helicases.     

In vitro and in vivo gene delivery by recombinant baculoviruses

Although recombinant baculovirus vectors can be an efficient tool for gene transfer into mammalian cells in vitro, gene transduction in vivo has been hampered by the inactivation of baculoviruses by serum complement. Recombinant baculoviruses possessing excess envelope protein gp64 or other viral envelope proteins on the virion surface deliver foreign genes into a variety of mammalian cell lines more efficiently than the unmodified baculovirus. In this study, we examined the efficiency of gene transfer both in vitro and in vivo by recombinant baculoviruses possessing envelope proteins derived from either vesicular stomatitis virus (VSVG) or rabies virus. These recombinant viruses efficiently transferred reporter genes into neural cell lines, primary rat neural cells, and primary mouse osteal cells in vitro. The VSVG-modified baculovirus exhibited greater resistance to inactivation by animal sera than the unmodified baculovirus. A synthetic inhibitor of the complement activation pathway circumvented the serum inactivation of the unmodified baculovirus. Furthermore, the VSVG-modified baculovirus could transduce a reporter gene into the cerebral cortex and testis of mice by direct inoculation in vivo. These results suggest the possible use of the recombinant baculovirus vectors in combination with the administration of complement inhibitors for in vivo gene therapy.