Mini M13 bacteriophage: circular fragments of M13 DNA are replicated and packaged during normal infections

M13 filaments, 0.2–0.5 of the standard length consitituted 20% of a large stock of phages obtained after 8 passages beyond the initial single-plaque isolation. The mini particles, purified by sucrose velocity sedimentation, contain circular, single-strand DNA of 0.2–0.5 the normal length. The particles are reproduced only upon coinfection with normal M13. Infection with an equal number of mini and full-size M13 particles generated a majority of mini forms among the intracellular DNAs (duplex and single-stranded circles) and the released phage particles. Analysis of mini phage DNA by heteroduplex electron microscopy showed them to be fragments of the M13 circle containing the unique site for a restriction endonuclease and extending for a variable distance (about 0.2–0.5 unit length) in one direction from this site.     

Multivalent display system on filamentous bacteriophage pVII minor coat protein

The systems for display of foreign peptides and polypeptides on filamentous bacteriophage have exploited genetic fusion to all of the five coat proteins. Multivalent display systems allowing selection of low affinity antibody fragments have been devised for fusions to gene III. However, since pIII has to interact with the bacterial receptors during the infection process, reduced infectivity can be observed. Alternative display systems utilizing other coat protein have been examined. These, however, take advantage of phagemid systems, in which a mixture of fusion and non-fusion coat proteins becomes displayed, thus preventing multivalent display. In this paper, we describe genetically stable fusion of scFv fragments to gene VII directly in the phage genome, thus giving rise to a multivalent display system where infectivity is not comprised. A hundred-fold enrichments factor can be obtained in model selection. Our results demonstrate that the small size of pVII (33 amino acids) is not structurally compromised by fusion of scFv antibody fragments at their N-terminus, thus demonstrating the feasibility of utilizing pVII as a fusion partner.     

Monoclonal antibodies against the major coat protein of filamentous phage as a useful analytical tool for bacteriophage peptide/protein display

Four mouse monoclonal antibodies (MAbs) that react with filamentous M13KO7 and R408 phage were obtained. Three of these MAbs (two IgG2a and one IgG3) recognize linear sequences of the p8 main structural coat protein, and one (IgG2a) identifies a putatively conformational epitope, as suggested by Western blot. These MAbs also react with recombinant phage expressing peptide antigens fused to p8, and are though useful reagents for peptide/protein phage display screening based methods. The latter was shown in an enzyme-linked immunoadsorbent assay (ELISA) and a visual immunoassay where one of the anti-p8 MAbs was used to capture recombinant phages displaying a peptide characteristic of the Hepatitis B virus surface antigen or a Dengue virus-related peptide antigen.     

Selection of specific phage from display libraries: monoclonal antibody against VCS M13 helper phage coat protein III (gIIIp).

Screening of specific phage is often hampered by nonspecific binding either of the VCS M13 helper phage to the solid phase absorbent or to the polyclonal antibodies used for selection. The former is improved by increasing the stringency for selection. However, the available polyclonal anti-VCS M13 antibodies often react with immobilized antigen nonspecifically, making it difficult to distinguish between positive and negative clones. To improve this selection process, a monoclonal antibody (MAb) was produced which recognizes ligand-coat protein three (gIIIp) on the helper phage VCS M13. This MAb is highly sensitive and specific, and it is useful for selecting relevant clones. This reagent should find widespread application in identifying interactive clones from a variety of phage display libraries.     

Removal of the coat protein of bacteriophages M13 or fd from the exterior of the host after infection

The protein coat of the filamentous DNA-containing bacteriophages M13 and fd could be removed from the exterior of the host cell after successful infection had been initiated. M13 and fd thus behaved similarily to other known Escherichia coli bacteriophages. If the disassembled coat protein subunits were not removed from the surface of the infected cell, they were eventually ingested and utilized by the host and appeared partially in progeny phage.     

Immunodiagnosis of Citrus leprosis virus C using a polyclonal antibody to an expressed putative coat protein

Citrus leprosis virus C (CiLV-C), a causal agent for citrus leprosis disease, is present in South and Central America and is a threat for introduction into the U.S. citrus industry. A specific, inexpensive and reliable antibody based detection system is needed for the rapid identification of CiLV-C. The CiLV-C is very labile and has not been purified in sufficient amount for antibody production. The p29 gene of CiLV-C genome that codes for the putative coat protein (PCP) was codon optimized for expression in Escherichia coli and synthesized in vitro. The optimized gene was sub-cloned into the bacterial expression vector pDEST17 and transferred into E. coli BL21AI competent cells. The expression of PCP containing N-terminal His-tag was optimized by induction with l-arabinose. Induced cells were disrupted by sonication and expressed PCP was purified by affinity chromatography using Ni-NTA agarose. The purified expressed PCP was then used as an immunogen for injections into rabbits to produce polyclonal antibody (PAb). The PAb specific to the expressed PCP was identified using Western blotting. The antibody was successfully used to detect CiLV-C in the symptomatic CiLV-C infected tissues using double antibody sandwich-enzyme-linked-immunosorbent (DAS-ELISA), indirect ELISA and dot-blot immunoassay (DBIA) formats.     

Detection of infectious myonecrosis virus using monoclonal antibody specific to N and C fragments of the capsid protein expressed heterologously

The gene encoding the capsid protein in ORF1 of the genome of infectious myonecrosis virus (IMNV) (GenBank AY570982) was amplified into three parts named CP-N (nucleotides 2248-3045), CP-I (nucleotides 3046-3954) and CP-C (nucleotides 3955-4953). The CP-N fragment was inserted into expression vector pTYB1 while CP-I and CP-C were each inserted into expression vector pGEX-6P-1 for transformation of BL21 E. coli strain. After induction, intein-CP-N (84 kDa), glutathione-S-transferase (GST)-CP-I (60 kDa) and GST-CP-C (62 kDa) fusion proteins were produced. They were separated by SDS-PAGE and electroeluted before immunization of Swiss mice for monoclonal antibody (MAb) production. Two MAbs specific to CP-N and one MAb specific to CP-C were selected for use for detection of natural IMNV infections in Penaeus vannamei by dot blotting, Western blotting and immunohistochemistry. There was no cross-reaction with shrimp tissues or common shrimp viruses including white spot syndrome virus (WSSV), yellow head virus (YHV), Taura syndrome virus (TSV), Penaeus monodon nucleopolyhedrovirus (PemoNPV), Penaeus stylirostris densovirus (PstDNV) and Penaeus monodon densovirus (PmDNV). The detection sensitivities of the MAbs were approximately 6 fmol/spot of purified recombinant intein-CP-N protein and 8 fmol/spot of GST-CP-C as determined by dot blotting. A combination of all three MAbs resulted in a twofold increase in sensitivity over use of any single MAb. However, this sensitivity was approximately 10 times lower than that of one-step RT-PCR using the same sample. Immunohistochemical analysis using MAbs specific to CP-N and CP-C in IMNV-infected shrimp revealed intense staining patterns in muscles, the lymphoid organ, gills, the heart, hemocytes and connective tissue.     

Down-regulation of class II major histocompatibility complex molecules on antigen-presenting cells by antibody fragments

Certain HLA class II-specific monoclonal antibodies (mAb) cause up to 90% decrease in the cell surface expression of class II molecules. This down-regulation is isotype-specific, i.e. DR-specific mAb do not affect the expression of DP and DQ molecules. However, antibodies binding to one DR allotype down-regulate both allotypes in heterozygous antigen-presenting cells (APC), indicating that the phenomenon is not a direct consequence of ligation. All down-regulating mAb identified recognize the first (peptide binding) domains of class II heterodimers, and strongly inhibit the activation of class II-restricted human T cells in vitro. Conversely, non-down-regulating mAb fail to inhibit T cell activation, and most of them (four out of five) recognize class II second domains. Down-regulating antibodies are cytotoxic for B lymphoblastoid cell lines and for a small proportion of normal activated B cells. Their F(ab′)₂ fragments mediate both down-regulation and cytotoxicity, whereas the monovalent Fab fragments are not cytotoxic, but retain the down-regulatory and T cell inhibitory properties. These findings raise the possibility of a class II major histocompatibility complex-specific, antibody-based immunosuppressive therapy without cytotoxic side effects.     

Molecular basis of the am8H1 lesion in bacteriophage M13.

The nucleotide sequence of the mutant region of am8H1, the only conditional lethal mutant in gene VIII of the filamentous phages, has been determined and compared to the wild-type sequence. The amber mutation lies adjacent to the codons specifying the cleavage site for the procaryotic signal peptidase (1). The precoat protein of this mutant appears to be processed normally in the amber-suppressing strain K37, which inserts a serine residue in place of a glutamic acid residue present in the wild-type precoat protein. The amino acid compositions of wild-type and mutant phage are in agreement with the sequence data.     

睾丸高表达蛋白质HSD13调节CHO细胞系周期进程

 目的 研究HSD13蛋白的组织表达定位及其对细胞周期的影响。方法 利用王琳芳教授实验室构建的人睾丸特异ESTs文库,通过电子克隆方法获得一新基因命名为HSD13。通过Northern和Western印迹方法检测HSD13蛋白在不同组织中的表达,并用免疫组化观察其在小鼠睾丸组织中的表达定位。通过构建HSD13过表达的CHO稳定细胞系,用双胸苷阻断法并结合流式细胞术检测对细胞周期的影响。结果 电子克隆获得HSD13基因。HSD13蛋白在睾丸组织中高表达,主要定位于生精细胞中的精原细胞和初级精母细胞。成功构建HSD13过表达和对照的CHO稳定细胞株,过表达HSD13蛋白可以显著加快细胞G2/M期进程。结论 HSD13蛋白于睾丸中精子发生早期表达,其过表达能够加速细胞周期进程。     

人磷脂转移蛋白的原核表达及其抗体的制备与鉴定

目的利用大肠杆菌表达人磷脂转移蛋白(PLTP),制备兔抗人PLTP的多克隆抗血清。方法采用RT-PCR技术,将人PLTP蛋白编码序列克隆入pET-30b(+)原核表达载体,转化大肠杆菌,IPTG诱导表达,切胶纯化蛋白后免疫家兔,制备PLTP抗血清。用间接ELISA法、Western blot、细胞免疫荧光检测对抗血清效价及特异性进行鉴定。结果SDS-PAGE分析表明,PLTP基因在大肠杆菌BL21(DE3)菌株的包涵体中高效表达,最佳诱导表达时间为3h;将纯化的蛋白免疫家兔,ELISA法测定的抗血清效价为1∶256000;Western blot及细胞免疫荧光检测显示,抗血清可以与PLTP原核及真核表达蛋白特异结合。结论成功地将PLTP进行了原核表达,制备了高效价、高特异性的兔抗人PLTP抗血清,为PLTP的临床检测及其结构与功能的进一步研究提供了有力工具。