Expression of poliovirus capsid polypeptide VP1 in Escherichia coli

Protection against lethal enterovirus 71 infection in newborn mice by passive immunization with subunit VP1 vaccines and inactivated virus

Enterovirus 71 (EV71), the newest member of Enteroviridae, is notable for its etiological role in epidemics of severe neurological diseases in children. Developing effective vaccines is considered a top choice among all control measures. We compared the inactivated virus vaccine (10 microg protein/mouse) with subunit vaccines--VP1 DNA vaccine (100 microg/mouse) or recombinant VP1 protein (10 microg/mouse)--in its ability to elicit maternal antibody and to provide protection against lethal infection of EV71 in suckling mice. Prior to gestation, all three groups of vaccinated dams possessed similar levels of neutralizing antibody. With a challenge dose of 2300 LD(50) virus/mouse, suckling mice born to dams immunized with inactivated virus showed 80% survival. The subunit vaccines provided protection only at a lower challenge dosage of 230 LD(50) per mouse, with 40% survival for DNA vaccine and 80% survival for VP1 protein. The cytokine profile produced by splenocytes showed a high level of IL-4 in the inactivated virus group, high levels of IFN-gamma and IL-12 in the DNA vaccine group, and high levels of IL-10 and IFN-gamma in the VP1 protein group. Overall, the inactivated virus elicited a much greater magnitude of immune response than the subunit vaccines, including total IgG, all four IgG subtypes, and T-helper-cell responses; these antibodies were shown to be protective against lethal infection when passively transferred to susceptible newborn mice. Our data indicated that inactivated virus is the choice of vaccine preparation capable of fulfilling the demand for effective control, and that VP1 subunit vaccines remain promising vaccine strategies that require further refinement.

TGATG vector: a new expression system for cloned foreign genes in Escherichia coli cells

A TGATG vector system was developed that allows for the construction of hybrid operons with partially overlapping genes, employing the effects of translational coupling to optimize expression of cloned cistrons in Escherichia coli. In this vector system (plasmid pPR-TGATG-1), the coding region of a foreign gene is attached to the ATG codon situated on the vector, to form the hybrid operon transcribed from the phage lambda PR promoter. The cloned gene is the distal cistron of this hybrid operon ('overlappon'). The efficiently translated cro'-cat'-'trpE hybrid cistron is proximal to the promoter. The coding region of this artificial fused cistron [the length of the corresponding open reading frame is about 120 amino acids (aa)] includes the following: the N-terminal portions of phage lambda Cro protein (20 aa), the CAT protein of E. coli (72 aa) and 3' C-terminal codons of the E. coli trpE gene product. At the 3'-end of the cro'-cat'-'trpE fused cistron there is a region for efficient translation reinitiation: a Shine-Dalgarno sequence of the E. coli trpD gene and the overlapping stop and start codons (TGATG). In this sequence, the last G is the first nucleotide of the unique SacI-recognition site (GAGCT decreases C) and so integration of the structural part of the foreign gene into the vector plasmid may be performed using blunt-end DNA linking after the treatment of pPR-TGATG-1 with SacI and E. coli DNA polymerase I or its Klenow fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of a poliovirus type 1 neutralization epitope on a diphtheria toxin fusion protein

The diphtheria toxin (DT) secreted by Corynebacterium diphtheriae is used after formolization as an efficient vaccine against diphtheria. In an attempt to evaluate its capacity to present heterologous peptide sequence in a recognized form, we created in-phase insertion in the gene encoding the non-toxic mutant protein CRM228 of DT. The sequence chosen for insertion was the synthetic DNA fragment encoding a poliovirus neutralization epitope. Tripartite fusion proteins comprising the mutant DT, the poliovirus peptide and beta-galactosidase were obtained in E. coli and purified by affinity chromatography. These fusion proteins reacted both with antibodies directed against the DT and a poliovirus specific monoclonal antibody. Moreover, these hybrid toxins induced protective antibodies against the lethal effect of DT and neutralizing antibodies against poliovirus. We conclude that the modification of highly immunogenic DT may provide a means for the presentation of foreign peptide sequences to the immune system.

Construction and characterization of hybrid hepatitis B antigen particles carrying a poliovirus immunogen

The hepatitis B surface antigen (HBsAg) has the unique property of assembling with cellular lipids into spherical or elongated particles of 22 nm diameter which are secreted by mammalian cells expressing HBsAg. We have studied the structural requirements for particle formation and secretion by creating in-phase insertions into different regions of the S gene of the hepatitis B virus, coding for HBsAg. Modified genes were integrated into an appropriate vector and expressed in mouse L cells. Various single and double inserts in the two major hydrophilic domains of HBsAg were compatible with particle synthesis and secretion. The level of secretion was influenced by the length of the insert, its primary structure, and the site of insertion into the HBsAg molecule. One of the inserted sequences was a synthetic DNA fragment encoding a continuous type 1 poliovirus neutralization epitope (the C3 epitope). Mammalian cells expressing the modified hepatitis B virus S gene secreted hybrid particles carrying the poliovirus antigen. The hybrid polio-HBsAg particles reacted with a monoclonal antibody specific for the C3 epitope and induced poliovirus neutralizing antibodies at low, but significant, titers in mice and at high titers in rabbits. However, the immune response to HBsAg was weaker to hybrid particles than to unmodified HBsAg particles. By cotransfection with two different plasmids carrying either modified or unmodified genes, we obtained phenotypically mixed particles containing both polio-HBsAg and HBsAg molecules. Inoculated into rabbits, the mixed particles induced high antibody titers against both poliovirus and HBsAg.

A general method for retrieving the components of a genetically engineered fusion protein

Escherichia coli expression vectors encoding an acid-labile aspartyl-proline (Asp-Pro) dipeptide bridging two protein sequences were constructed and used to synthesize two different bovine growth hormone (bGH) fusion proteins. The codons GAT-CCX coding for Asp-Pro are provided by the recognition site for Bam HI (GGATCC). Treatment of the bGH fusion proteins at low pH in the presence of guanidine hydrochloride releases the bGH moiety from the fusion protein. The release of the bGH from the fusion protein specifically requires the Asp-Pro dipeptide linking the bGH sequence to the fusion protein. The bGH released from the fusion protein retains anti-bGH immunoreactivity as well as the ability to bind to growth hormone receptor in vitro.

Induction by synthetic peptides of broadly reactive, type-specific neutralizing antibody to poliovirus type 3

A region of virus capsid protein VP1 located 89-100 amino acids from the N-terminus has been proposed to comprise a major antigenic site involved in the neutralization of poliovirus type 3. Synthetic peptides 10-18 amino acids in length, containing all or part of this sequence, were tested for their ability to induce antiviral antibodies. Rabbits, but not guinea pigs or mice, immunized with the most active peptide, developed hightitered, type-specific, neutralizing antibodies for a wide range of poliovirus type 3 strains. Consistent with the broad type specificity of the antibody response was the observation that amino acids 89-100 of VP1 are highly conserved among different poliovirus type 3 strains. This sequence thus appears to provide, at least in part, a molecular basis for serotype antigenic specificity. Individual amino acids from 93 to 98 within this sequence were shown to be important for the neutralization of virus by antipeptide sera by examination of the ability of the sera to neutralize laboratory-derived poliovirus type 3 mutants with known single amino acid substitutions in the proposed antigenic site.

Nuclear localization of poliovirus capsid polypeptide VP1 expressed as a fusion protein with SV40-VP1

The poliovirus cDNA fragment coding for capsid polypeptide VP1 was inserted between the EcoRI and BamHI sites of SV40 DNA, generating a chimaeric gene in which the sequence of the 302 amino acids (aa) of poliovirus capsid polypeptide VP1 was placed downstream from that of the 94 N-terminal aa of SV40 capsid polypeptide VP1. The resulting defective, hybrid virus, SV40-delta 1 polio, was propagated in CV1 cells using an early SV40 mutant, am404, as a helper. Cells doubly infected by SV40-delta 1 polio and am404 expressed a 50-kDal fusion protein which was specifically immunoprecipitated by polyclonal and/or monoclonal antibodies raised against poliovirus capsids or against poliovirus polypeptide VP1. Examination of the infected cells by immunofluorescence after staining with anti-poliovirus VP1 immune sera revealed that the fusion protein was mostly located in the intra- and perinuclear space of the cells, in contrast to the exclusively intracytoplasmic location of genuine poliovirus VP1 polypeptide that was observed in poliovirus-infected cells. This suggests that the N-terminal part of the SV40-VP1 polypeptide could contain an important sequence element acting as a migration signal for the transport of proteins from the cytoplasm to the nucleus.

Localization of a poliovirus type 1 neutralization epitope in viral capsid polypeptide VP1

Poliovirus type 1 cDNA sequences coding for viral capsid polypeptide VP1 were inserted into the beta-lactamase sequence of Escherichia coli plasmid pBR322. Resulting recombinant plasmid pSW119 expressed in Escherichia coli a VP1-beta-lactamase fusion protein that reacted with antibodies raised against poliovirus capsid polypeptide VP1 and with a monoclonal poliovirus type 1 neutralizing antibody, C3. Deletions of various lengths were generated within the VP1 sequence. The hybrid proteins expressed by the deleted plasmids did not react any more with C3 when the region of VP1 amino acids 95-110 (poliovirus nucleotides 2,754-2,806) was deleted. Therefore, the C3 epitope responsible for virus neutralization is most probably located in this region of the capsid polypeptide.