The Chimeric Chaoyang-Zika Vaccine Candidate Is Safe and Protective in Mice.

Zika virus (ZIKV) is an emerging flavivirus that causes congenital syndromes including microcephaly and fetal demise in pregnant women. No commercial vaccines against ZIKV are currently available. We previously generated a chimeric ZIKV (ChinZIKV) based on the Chaoyang virus (CYV) by replacing the prME protein of CYV with that of a contemporary ZIKV strain GZ01. Herein, we evaluated this vaccine candidate in a mouse model and showed that ChinZIKV was totally safe in both adult and suckling immunodeficient mice. No viral RNA was detected in the serum of mice inoculated with ChinZIKV. All of the mice inoculated with ChinZIKV survived, while mice inoculated with ZIKV succumbed to infection in 8 days. A single dose of ChinZIKV partially protected mice against lethal ZIKV challenge. In contrast, all the control PBS-immunized mice succumbed to infection after ZIKV challenge. Our results warrant further development of ChinZIKV as a vaccine candidate in clinical trials.

Rapid Generation of Recombinant Flaviviruses Using Circular Polymerase Extension Reaction.

The genus Flavivirus is a group of arthropod-borne single-stranded RNA viruses, which includes important human and animal pathogens such as Japanese encephalitis virus (JEV), Zika virus (ZIKV), Dengue virus (DENV), yellow fever virus (YFV), West Nile virus (WNV), and Tick-borne encephalitis virus (TBEV). Reverse genetics has been a useful tool for understanding biological properties and the pathogenesis of flaviviruses. However, the conventional construction of full-length infectious clones for flavivirus is time-consuming and difficult due to the toxicity of the flavivirus genome to E. coli. Herein, we applied a simple, rapid, and bacterium-free circular polymerase extension reaction (CPER) method to synthesize recombinant flaviviruses in vertebrate cells as well as insect cells. We started with the de novo synthesis of the JEV vaccine strain SA-14-14-2 in Vero cells using CPER, and then modified the CPER method to recover insect-specific flaviviruses (ISFs) in mosquito C6/36 cells. Chimeric Zika virus (ChinZIKV) based on the Chaoyang virus (CYV) backbone and the Culex flavivirus reporter virus expressing green fluorescent protein (CxFV-GFP) were subsequently rescued in C6/36 cells. CPER is a simple method for the rapid generation of flaviviruses and other potential RNA viruses. A CPER-based recovery system for flaviviruses of different host ranges was established, which would facilitate the development of countermeasures against flavivirus outbreaks in the future.

Immunological characterisation and immunoprotective efficacy of functional domain antigens of botulinum neurotoxin serotype A.

Botulinum neurotoxins (BoNTs) are highly toxic proteins that mediate their effects by binding to neuronal receptors and block the neutralizing ability of therapeutic antibodies. Vaccination is currently the most effective strategy to prevent botulism. In this study, a series of recombinant functional domain antigens of BoNT/A were prepared and identified, and their immunoprotective efficacies were explored and compared. Our results showed that all antigens produced strong humoral immune responses, although their protective effects against the toxin were different. Only the Hc and HN-L antigens produced strong protective effects and afforded complete immunoprotection. In addition, the combined vaccine groups showed that there was no synergistic effect on immune responses after antigen combination, suggesting that the integrity of the toxin antigen or domain is crucial to the immune effects. Studies of the dose-dependent immunoprotective effects further confirmed that the Hc domain antigen afforded more effective protective potency than the HN-L antigen, equivalent to the immune effect of the full-length toxin (Hc + HN-L combination group). Overall, our results demonstrated that the Hc domain elicited a strong protective immune response and also provided basic data and theoretical support for the development of Hc-based BoNT/A subunit vaccine. Therefore, the receptor binding domain Hc is implicated as a promising target antigen of the BoNT/A recombinant subunit vaccine as an alternative to the toxoid vaccine.

Production and radioprotective effects of pyrroloquinoline quinone.

Pyrroloquinoline quinone (PQQ) was produced by fermentation of the Methylovorus sp. MP688 strain and purified by ion-exchange chromatography, crystallization and recrystallization. The yield of PQQ reached approximately 125 mg/L and highly pure PQQ was obtained. To determine the optimum dose of PQQ for radioprotection, three doses (2 mg/kg, 4 mg/kg, 8 mg/kg) of PQQ were orally administrated to the experimental animals subjected to a lethal dose of 8.0 Gy in survival test. Survival of mice in the irradiation + PQQ (4 mg/kg) group was found to be significantly higher in comparison with the irradiation and irradiation + nilestriol (10 mg/kg) groups. The numbers of hematocytes and bone marrow cells were measured for 21 days after sublethal 4 Gy gamma-ray irradiation with per os of 4 mg/kg of PQQ. The recovery of white blood cells, reticulocytes and bone marrow cells in the irradiation + PQQ group was faster than that in the irradiation group. Furthermore, the recovery of bone marrow cell in the irradiation + PQQ group was superior to that in irradiation + nilestriol group. Our results clearly indicate favourable effects on survival under higher lethal radiation doses and the ability of pyrroloquinoline quinine to enhance haemopoietic recovery after sublethal radiation exposure.

Complete genome sequence of the bacterium Methylovorus sp. strain MP688, a high-level producer of pyrroloquinolone quinone.

Methylotrophic bacteria are widespread microbes which can use one carbon compound as their only carbon and energy sources. Here we report the finished, annotated genome sequence of the methylotrophic bacterium Methylovorus sp. strain MP688, which was isolated from soil for high-level production of pyrroloquinolone quinone (PQQ) in our lab.

Complete genome sequence of the bacterium Ketogulonicigenium vulgare Y25.

Ketogulonicigenium vulgare is characterized by the efficient production of 2KGA from L-sorbose. Ketogulonicigenium vulgare Y25 is known as a 2-keto-L-gulonic acid-producing strain in the vitamin C industry. Here we report the finished, annotated genome sequence of Ketogulonicigenium vulgare Y25.

Degradation of HSA-AX15(R13K) when expressed in Pichia pastoris can be reduced via the disruption of YPS1 gene in this yeast.

Expression of recombinant protein HSA-AX15(R13K) in Pichia pastoris GS115 strain produced both the intact protein and its two degradation products with molecular weights of around 43kDa and 66.2kDa, respectively. To reduce or avoid the degradation, a modified P. pastoris GS115 stain, in which YPS1 gene was disrupted, was constructed via homologous recombination and used as a host strain for the HSA-AX15(R13K) expression. After 60h of induction during culture, it was found that the degradation product of around 66.2kDa was reduced significantly in the supernatant of yps1-disrupted strain compared with that in the supernatant of wild-type strain. By the Western blot analysis of culture supernatants from wild-type and yps1-disrupted strains expressing HSA-AX15(R13K), the significant improvement was also seen in the degradation product of around 43kDa. Comparison of cell growth between the two strains demonstrated a similar growth tendency, thereby indicating that the disruption of YPS1 gene has no effect on the normal physiology of GS115 strain. Following induction for 60h, the yield of intact HSA-AX15(R13K) in the yps1 disruptant was three-fold higher than that in the wild-type strain. Therefore, such a P. pastoris mutant deficient in YPS1 activity is suitable for the high-level expression of recombinant protein HSA-AX15(R13K).

Increasing the homogeneity, stability and activity of human serum albumin and interferon-alpha2b fusion protein by linker engineering.

Previous studies in our laboratory have shown that when the N-terminus of interferon-alpha2b (IFN-alpha2b) was directly fused of to the C-terminus of human serum albumin (HSA), the resultant fusion protein (HSA-IFN-alpha2b) was heterogeneous (migrated as doublets on non-reducing SDS-PAGE) and unstable (prone to form covalent aggregates). The heterogeneity and instability of HSA-IFN-alpha2b was ascribed to the structural disturbance between HSA and IFN-alpha2b. To alleviate such structural disturbance, linkers with different lengths (1, 2, 5, 10 amino acid residues) or different conformation (flexible linker (FL, GGGGS), rigid linker (RL, PAPAP) or helix-forming linker (HL, AEAAAKEAAAKA)) were inserted between HSA and IFN-alpha2b. It was demonstrated that linker with 5 amino acid residues was sufficient to separated HSA and IFN-alpha2b effectively, as fusion protein with this linker migrated as single band on non-reducing SDS-PAGE. The fusion proteins with FL, RL and HL linkers were purified to homogeneity with yields of 20%, while the recovery rate of HSA-IFN-alpha2b was only 10%. Accelerated thermal stress tests showed that in contrast to HSA-IFN-alpha2b, fusion proteins with FL, RL and HL linkers were free of aggregates after stored at 37 degrees C for 10 days. Stability tests also revealed that fusion proteins with FL, RL and HL linkers had different susceptibility to hydrolysis, with HSA-RL-IFN-alpha2b being the least susceptible to hydrolysis at pH 6 and 7. Activity assay revealed that the insertion of FL, RL and HL linkers increased the anti-viral activity of fusion protein by 39%, 68% and 115%, respectively.

Disruption of Pichia pastoris PMR1 gene decreases its folding capacity on human serum albumin and interferon-alpha2b fusion protein.

In an attempt to increase the secretion capacity of Pichia pastoris (Pp), PpPMR1 gene was disrupted with GS115 as parent strain, and the resultant mutant was designated as Pppmr1. Pppmr1 displayed a Ca2+-dependent growth defect, which was consistent with the PMR1 mutation in other yeasts. HSA-L5-IFNalpha2b, a human serum albumin (HSA) and inferferon-alpha2b (IFNalpha2b) fusion protein with a flexible linker of 5 amino acid residues, was employed as a reporter to study the effects of PpPMR1 disruption on the secretion of heterologous protein. Because of its decreased viability after induction, Pppmr1 secreted more HSA-L5-IFNalpha2b only during the early phase (the first 15 hours) of induction. Although HSA-L5-IFNalpha2b secreted from GS115 and Pppmr1 had similar antiviral activity, the latter was heterogeneous (migrated as doublets on non-reducing SDS-PAGE) and unstable (prone to aggregation at neutral to mild alkaline pH). Site-directed mutagenesis revealed that the heterogeneity of HSA-L5-IFNalpha2b secreted from Pppmr1 was originated from the incomplete disulphide bridge pairing between Cys1 and Cys98 of IFNalpha2b. To be secreted homogeneously from Pppmr1 and to be stable in aqueous solution, the linker of the fusion protein should be extended to 10 amino acid residues.

Circumventing the heterogeneity and instability of human serum albumin-interferon-alpha2b fusion protein by altering its orientation.

Albuferon is a novel long-acting interferon resulted from the direct genetic fusion of human albumin and interferon-alpha2b (HSA-IFN-alpha2b). Albuferon, co-developed by Human Genome Sciences Inc. and Novartis, is currently in late stage development for the treatment of hepatitis C. It was unexpected that HSA-IFN-alpha2b secreted from Pichia pastoris migrated as doublets on non-reducing SDS-PAGE and was prone to form covalent aggregates in aqueous solution. The heterogeneity and instability of HSA-IFN-alpha2b lowered its recovery rate to about 10% and necessitated lyophilized formulation. Site-directed mutagenesis revealed that the heterogeneity and instability of HSA-IFN-alpha2b was caused by the incomplete disulfide bridge formation between Cys1 and Cys98 of IFN-alpha2b. To alleviate the structural perturbation of IFN-alpha2b by HSA, IFN-alpha2b-HSA fusion protein, in which IFN-alpha2b was located at the N-terminus, was created. IFN-alpha2b-HSA was shown to be homogeneous and stable at 37 degrees C for at least 10 days. The improved homogeneity and stability of IFN-alpha2b-HSA increased the recovery rate by 2.5-fold and made the development of stable solution formulation possible. In vitro antiviral assays showed that both fusion proteins retained the activity of IFN-alpha2b, and the EC(50) of HSA-IFN-alpha2b, and IFN-alpha2b-HSA was calculated to be 120+/-12.5, and 160+/-1 1.3ng/ml, respectively. The increased recovery rate and the possibility of solution formulation of IFN-alpha2b-HSA may compensate for its slightly decreased in vitro activity, and makes it to be a promising therapeutic agent that deserves further evaluation.

Recombinant heat shock protein 65 carrying hepatitis B core antigen induces HBcAg-specific CTL response.

Many studies have provided evidence that heat shock protein 65 (Hsp65) can elicit potent specific cellular adaptive immune responses (e.g. CD8(+) cytotoxic T-cell effectors or classic CTLs) based on their ability to chaperone antigenic peptides. Hsp65 is thus an effective carrier for heterologous peptide epitopes for therapeutic vaccines against cancer or chronic infectious diseases. The core antigen of hepatitis B virus (HBcAg) is extremely immunogenic, and functions as both a T-cell-dependent and a T-cell-independent antigen. Therefore, HBcAg may be a promising candidate target for therapeutic vaccine control of chronic HBV infection. Here, a chimeric protein, Hsp65Bc, was created by fusing the HBcAg sequence to the carboxyl terminus of the Hsp65 sequence in E. coli. Analysis of its antigenicity and immunogenicity revealed that HBc epitopes are surface accessible. Hsp65Bc induced moderate anti-HBc immune responses as well as a strong specific T-cell response in BALB/c mice. These results indicate that Hsp65Bc may have potential as a vaccine for treatment of HBV chronic infection.

Enhanced secretion of heterologous proteins in Pichia pastoris following overexpression of Saccharomyces cerevisiae chaperone proteins.

In Pichia pastoris, secretory proteins are folded and assembled in the endoplasmic reticulum (ER). However, upon introduction of foreign proteins, heterologous proteins are often retained in the cytoplasm or in the ER as a result of suboptimal folding conditions, leading to protein aggregation. The Hsp70 and Hsp40 chaperone families in the cytoplasm or in ER importantly regulate the folding and secretion of heterologous proteins. However, it is not clear which single chaperone is most important or which combination optimally cooperates in this process. In the present study we evaluated the role of the chaperones Kar2p, Sec63, YDJ1p, Ssa1p, and PDI from Saccharomyces cerevisiae. We found that the introduction of Kar2p, Ssa1p, or PDI improves protein secretion 4-7 times. In addition, we found that the combination chaperones of YDJ1p/PDI, YDJ1p/Sec63, and Kar2p/PDI synergistically increase secretion levels 8.7, 7.6, and 6.5 times, respectively. Therefore, additional integration of chaperone genes can improve the secretory expression of the heterologous protein. Western blot experiments revealed that the chaperones partly relieved the secretion bottleneck resulting from foreign protein introduction in P. pastoris. Therefore, the findings from the present study demonstrate the presence of a network of chaperones in vivo, which may act synergistically to increase recombinant protein yields.

Construction and evaluation of anti-gastrin immunogen based on P64K protein.

AIM: To construct two kinds of anti-gastrin immunogen based on P64K protein from Neisseria meningitids and to compare their immunogenic effect. METHODS: G17P64K gene was cloned and ligated into pET28a plasmid, then transformed into BL21(DE3). After inoculation of LB medium and IPTG induction, the recombinant protein was solubly expressed at a high level. The purification of G17P64K fusion protein was similar to that of P64K. An initial step of purification consisting of 30% saturated ammonium sulfate precipitation was done. Additional fine optimizations included phenyl-sepharose, G200 Sephadex gel filtration and Q-sepharose anion exchanger chromatography. Highly purified protein was obtained and sequenced at the N-terminal amino acid residues. Polypeptide was synthesized by Fmoc solid phase chemical method and cross-linked to carrier protein P64K and DT mutant by MBS method and then the rabbit anti-gastrin 17 antibody was prepared by immunizing rabbit with cross-linked and fused protein. The titer and the activity in vitro of antibody were assessed. RESULTS: G17P64K gene and the recombinant bacteria were obtained. After four steps purification, protein sample that has the purity above 90% was achieved. At the 84(th) day after the first immunization, the titer of antibody against cross-linked protein reached 51,200. Evaluation of the antibody in vitro manifested that it had a high inhibitory activity on the growth of tumor cell SW480. CONCLUSION: The P64K-polypeptide cross-linked immunogen immunized rabbit and achieved a higher titer antibody against gastrin 17 than the G17P64K fusion protein immunogen, which could inhibit the growth of the tumor cell SW480.

[Purification and activity assay of HSA-AX15 (R13K) fusion protein expressed in Pichia pastoris].

To increase the in vivo half-life of human CNTF mutein AX15 (R13K), HSA-AX15 (R13K) fusion protein was constructed by the fusion of the C-terminus of HSA to the N-terminus of AX15 (R13K) via an 11 amino acids linker. HSA-AX15 (R13K) fusion protein was purified to homogeneity by cation exchange chromatography, reverse phase chromatography and gel filtration after expressed in pichia pastoris. TF-1 cell survival bioassay showed the biological activity of AX15 (R13K) was not affected by the fusion to HSA. It was demonstrated that tertian injection of 4.8 mg/kg HSA-AX15 (R13K) fusion protein could produce more potent anti-obesity effects on KM mice than daily injection of 1.6 mg/kg AX15 (R13K). The long-acting form of hCNTF variant has the potential to reduce discomfort by requiring fewer injections and to minimize the side-effects by decreasing the dosage and fluctuation of plasma concentration, and thus has superior clinical application.

[Construction of superagonist mutein of human CNTF and its expression in Pichia pastoris].

Human ciliary neurotrophic factor (hCNTF) and its derivatives are promising therapeutics for obesity associated with diabetes. To reduce its side effects and increase its efficacy, superagonist mutein of human CNTF was constructed by the introduction of S165D/Q166H mutation into AX15(R13K), which is a mutein of naturally occurring hCNTF, with improved biological activity, stability, solubility and KEX2 resistance. In vitro TF-1 cell survival assay and in vivo antiobesity tests showed DH-AX(R13K) was about 5 fold more potent than AX15(R13K). It was further demonstrated that the antiobesity effect of DH-AX15(R13K) was more durable than that of AX15(R13K). The more durable effects of DH-AX15(R13K) is ascribed to its higher specific activity, but not to its prolonged half-life. The superagonist mutein of human CNTF would have an improved side effect profile and thus have superior therapeutic potential.

Secretory expression and characterization of a recombinant-deleted variant of human hepatocyte growth factor in Pichia pastoris.

AIM: To study the secretory expression of human hepatocyte growth factor (hdHGF) gene in Pichia pastoris. METHODS: The full-length gene of human cDNA encoding the deleted variant of hdHGF was cloned by RT-PCR and overlapping-fragment PCR technique using mRNA of human placenta as a template. The cloned hdHGF cDNA was inserted into the Escherichia coli-yeast shuttle vector of pPIC9. The constructed plasmid, pPIC9-hdHGF, was transformed into the GS115 cells of the methylotrophic yeast, P pastoris, using a chemical method. The Mut(+ ) transformants were screened to obtain high-expression strains by the test and analysis of expressed products of shake-flask culture. A secretory form of rhdHGF was made with the aid of the leader peptide sequence of Saccharomyces cerevisiae alpha-factor. RESULTS: The expressed products, which showed a band of molecular mass of about 80 ku, were observed on 15% SDS-PAGE and identified by Western blotting and N-terminal amino acid sequencing. In the high cell density culture of 5 L fermentor by fed-batch culture protocol, the cell biomass was reached at approximately 135 g (DCW)/L. The productivity of secreted total supernant protein concentration attained a high-level expression of more than 8.0 g/L and the ratio of rhdHGF band area was about 12.3% of the total band area scanned by SDS-PAGE analysis, which estimated that the product of rhdHGF was 500-900 mg/L. CONCLUSION: The P pastoris system represents an attractive tool of generating large quantities of hdHGF for both research and industrial purposes.

[Construction of protease resistant mutein of human CNTF and its expression in Pichia pastoris].

AX15 is a mutein of naturally occurring human ciliary neurophic factor (hCNTF), with improved biological activity, stability and solubility. AX15 is susceptible to protease degradation when expressed in Pichia pastoris. Amino acid sequencing revealed the degradation was occurred behind position 12 and 13 amino acid residues, which constitute a dibasic site, RR. Based on the substrate specificity of KEX2, a KEX2 resistant mutein of AX15-AX15 (R13K) was constructed, in which RR was replaced by RK. It was demonstrated that the stability of AX15 (R13K) improved significantly, as no degradation was detected even after 120 hours of induction. AX15 (R13K) was purified to homogeneity by ultrafiltration and gel filtration. TF-1 cell survival bioassay showed AX15 (R13K) had equivalent specific activity to AX15. The protease resistant mutein of AX15 may have greater in vivo stability and thus have superior therapeutic potential.