Effects of the number of amino acid residues in the signal segment upstream or downstream of the NS2B-3 cleavage site on production and secretion of prM/M-E virus-like particles of West Nile virus.

Expression of genes for precursor M (prM) and envelope (E) proteins of West Nile virus (WNV) leads to the production of small, capsidless, and non-infectious virus-like particles (VLPs) possessing the E antigen which is responsible for viral entry and immune protection. It has been reported that processing of the secretion signal affects viral release. We examined the secretion efficiency of VLPs into the culture medium from RK13 or 293T cells transfected with expression vectors for prM and E proteins of WNV which were constructed to comprise different lengths of signal peptides upstream of the prM-E domain. The number of amino acid residues present in the segment markedly affected the production, processing, and secretion of VLPs. Secreted VLPs possessed both the processed M protein and the glycosylated E protein. In addition, immunization with VLPs induced neutralizing antibodies in C3H/HeN mice. These results indicate that the number of amino acid residues comprising the N-terminus of the signal segment controls the efficiency of assembly, maturation, and release of VLPs in the absence of viral protease, which in turn indicates the potential of VLPs as a candidate for an effective WNV subunit vaccine.

DNA sequence analysis of varicella-zoster virus gene 62 from subclinical infections in healthy children immunized with the Oka varicella vaccine.

A live attenuated varicella vaccine, the Oka vaccine strain (vOka), is routinely administered to children in Japan and other countries, including the United States. vOka consists of a mixture of genotypically distinct variants, but little is known about the growth potential of each variants in vivo. We isolated varicella-zoster virus (VZV) DNA sequences from the peripheral blood mononuclear cells (PBMCs) of asymptomatic healthy children immunized with the Oka varicella vaccine. VZV gene 62 DNA fragments were detected in 5 of 166 (3.0%) PBMC samples by nested PCR within 5 weeks of the vaccination. Sequence analysis of VZV DNA from these five PBMC samples indicated that multiple viral clones in the vaccine could infect vaccinees and replicate in vivo. We also provide evidence that a nonsynonymous substitution at position 105356 may affect viral replication in vivo.

Crystal structure of the catalytic domain of Japanese encephalitis virus NS3 helicase/nucleoside triphosphatase at a resolution of 1.8 A.

The NS3 protein of Japanese encephalitis virus (JEV) is a large multifunctional protein possessing protease, helicase, and nucleoside 5'-triphosphatase (NTPase) activities, and plays important roles in the processing of a viral polyprotein and replication. To clarify the enzymatic properties of NS3 protein from a structural point of view, an enzymatically active fragment of the JEV NTPase/helicase catalytic domain was expressed in bacteria and the crystal structure was determined at 1.8 A resolution. JEV helicase is composed of three domains, displays an asymmetric distribution of charges on its surface, and contains a tunnel large enough to accommodate single-stranded RNA. Each of the motifs I (Walker A motif), II (Walker B motif) and VI was composed of an NTP-binding pocket. Mutation analyses revealed that all of the residues in the Walker A motif (Gly(199), Lys(200) and Thr(201)), in addition to the polar residues within the NTP-binding pocket (Gln(457), Arg(461) and Arg(464)), and also Arg(458) in the outside of the pocket in the motif IV were crucial for ATPase and helicase activities and virus replication. Lys(200) was particularly indispensable, and could not be exchanged for other amino acid residues without sacrificing these activities. The structure of the NTP-binding pocket of JEV is well conserved in dengue virus and yellow fever virus, while different from that of hepatitis C virus. The detailed structural comparison among the viruses of the family Flaviviridae should help in clarifying the molecular mechanism of viral replication and in providing rationale for the development of appropriate therapeutics.

Japanese encephalitis subunit vaccine composed of virus-like envelope antigen particles purified from serum-free medium of a high-producer J12#26 cell clone.

A stable cell clone, J12#26, which continuously secretes large amounts of the envelope (E) antigen of Japanese encephalitis (JE) virus (J. Virol. 77 (2003) 8745) was adapted to serum-free medium. The J12#26 antigen possessed hemagglutinating activity, as well as the viral E and M proteins. More than 10 and 1mg of the antigen quantified with the licensed JE vaccine (JE-VAX) as a standard by E-ELISA and protein determination, respectively, were recovered from 500 ml of serum-free medium by membrane ultrafiltration, Sephacryl S-300 chromatography, sucrose gradient centrifugation and Sephadex G-25 chromatography. SDS-PAGE and Western blot analyses confirmed the high yield and purity of the J12#26 E antigen, which was comprised of small spherical virus-like particles (VLP) of approximately 25 nm in diameter. This antigen induced in mice without adjuvant neutralizing antibody (NT Ab) titers, as high as or higher than the licensed JE vaccine, and complete protection against challenge with wild-type virus. These results suggest that the J12#26 antigen is a promising second-generation JE subunit vaccine.

High-level expression of clostridial sialidase using a ferredoxin gene promoter-based plasmid.

A "large" sialidase isozyme (NanI) from Clostridium perfringens is a representative microbial sialidase with broad substrate specificity, being used for the analysis of sialoglycoconjugates. It is also a possible virulence factor. However, purification of the native enzyme in a large quantity is not practical due to its low productivity. To obtain the enzyme in a satisfactory yield, a gene encoding the NanI was transcriptionally fused to the fdx gene promoter (P(fdx)) in a shuttle-vector, pFF, and transformed into C. perfringens 13. The resultant strain released the enzyme into the culture medium, as the original strain does. The enzyme activity increased during the first 6 h of culture and thereafter remained at maximal levels. The maximal activity was approximately 3000-fold compared with that of the original strain, and 15-fold compared with that of recombinant Escherichia coli, which possesses extra copies of the tRNA gene for selected rare codons. This suggests the usefulness of a P(fdx)-based plasmid for expressing AT-rich genes in C. perfringens. The enzyme was successfully purified by two-step procedure with a specific activity of 2860 U/mg using 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid and a yield of 1.69 mg of NanI per 100 ml of culture. The method described here can facilitate purification of NanI in enough quality and quantity to analyze the role of sialoglycoconjugates in cells and the pathogenic importance of NanI sialidase.

Enhancement of immunity against VZV by giving live varicella vaccine to the elderly assessed by VZV skin test and IAHA, gpELISA antibody assay.

The enhancement of immunity against varicella-zoster vaccine (VZV) by subcutaneous injection of a live varicella vaccine was assessed by the VZV skin test for cell-mediated immunity (CMI), and immunoadherence hemagglutination assay (IAHA) and gpELISA antibody assays in the elderly people of 50-79 years of age. A total of 127 subjects were examined: 79 aged 50-59, 25 aged 60-69, and 25 aged 70-79. All were seropositive by the gpELISA assay (one was seronegative in the IAHA antibody assay). In contrast, a notable decline was observed in the VZV skin test with increasing age. Negative reaction was observed in 16/79 (20.2%) of the subjects in their 50s, 12/25 (48.0%) in their 60s and 14/25 (56.0%) in the 70s. After the vaccination, the results of the VZV skin test changed from negative to positive in 15/16 (91.8%) of subjects in their 50s, 11/12 (91.7%) in their 60s and 12/14 (85.7%) in their 70s. The mean antibody titer in the IAHA and the gpELISA increased approximately two-fold after the vaccination in each group. Immunity to VZV in 35 elderly subjects who were vaccinated previously was followed up for 4 years. All were positive by the VZV skin test after the previous vaccination. After 4 years, 31 (88.6%) were positive by the skin test, 4 were negative and became positive after revaccination. Although this study was uncontrolled open study, the results suggest that administering live varicella vaccine to the elderly is effective for enhancing immunity, particularly CMI to VZV.

Stable high-producer cell clone expressing virus-like particles of the Japanese encephalitis virus e protein for a second-generation subunit vaccine.

We produced and characterized a cell clone (J12#26 cells) that stably expresses Japanese encephalitis virus (JEV) cDNA, J12, which encodes the viral signal peptide, premembrane (prM), and envelope (E) proteins (amino acid positions 105 to 794). Rabbit kidney-derived RK13 cells were transfected with a J12 expression plasmid, selected by resistance to marker antibiotics, and cloned by two cycles of a limiting-dilution method in the presence of antibiotics, a procedure that prevents the successful generation of E-producing cell clones. J12#26 cells secreted virus-like particles containing the authentic E antigen (E-VLP) into the culture medium in a huge enzyme-linked immunosorbent assay-equivalent amount (2.5 micro g per 10(4) cells) to the internationally licensed JE vaccine JE-VAX. E-VLP production was stable after multiple cell passages and persisted over 1 year with 100% expressing cells without detectable cell fusion, apoptosis, or cell death, but was suspended when the cells grew to 100% confluency and contact inhibition occurred. Mice immunized with the purified J12#26 E-antigen without adjuvant developed high titers of neutralizing antibodies for at least 7 months and 100% protection against intraperitoneal challenge with 5 x 10(6) PFU of JEV when examined according to the JE vaccine standardization protocol. These results suggest that the recombinant E-VLP antigen produced by the J12#26 cell clone is an effective, safe, and low-cost second-generation subunit JE vaccine.

Measurement of HCV RdRp activity with C-terminal 21 aa truncated NS5b protein: optimization of assay conditions.

The non-structural protein 5b (NS5b) of hepatitis C virus (HCV), bearing an RNA-dependent RNA polymerase (RdRp) activity, is considered as a new target of antiviral therapy. We expressed and purified the C-terminal 21 amino acid truncated NS5b protein fused with glutathione S-transferase (GST-5bC21) using Escherichia coli. With the highly purified GST-5bC21 protein, we established an in vitro assay system for RdRp activity by using poly(C) as the template and a 12 mer oligo(rG) as the primer. The optimal conditions for testing various concentrations of template, primer and proteins were determined to 22 degrees C and a pH of 7.5. The addition of 2.5 mM Mn(2+) increased the activity profoundly, to a level fivefold higher than that in the presence of 10 mM Mg(2+). At higher concentrations of Mn(2+), GST-5bC21 is stable as compared with previously reported full-length NS5b expressed using insect cells or NS5b protein with the C-terminal 18 amino acids deleted. This sensitive and easy to use quantitative assay system will provide a stable system for the screening of inhibitors for HCV RdRp.