Cell surface-binding motifs of L2 that facilitate papillomavirus infection

Human papillomavirus type 16 (HPV16) is the primary etiologic agent of cervical carcinoma, whereas bovine papillomavirus type 1 (BPV1) causes benign fibropapillomas. However, the capsid proteins, L1 and L2, of these divergent papillomaviruses exhibit functional conservation. A peptide comprising residues 1 to 88 of BPV1 L2 binds to a variety of cell lines, but not to the monocyte-derived cell line D32, and blocks BPV1 infection of mouse C127 cells. Residues 13 to 31 of HPV16 L2 and BPV1 L2 residues 1 to 88 compete for binding to the cell surface, and their binding, unlike that of HPV16 L1/L2 virus-like particles, is unaffected by heparinase or trypsin pretreatment of HeLa cells. A fusion of HPV16 L2 peptide 13-31 and GFP binds (K(d), approximately 1 nM) to approximately 45,000 receptors per HeLa cell. Furthermore, mutation of L2 residues 18 and 19 or 21 and 22 significantly reduces both the ability of the HPV16 L2 13-31-GFP fusion protein to bind to SiHa cells and the infectivity of HPV16 pseudovirions. Antibody to BPV1 L2 peptides comprising residues 115 to 135 binds to intact BPV1 virions, but fails to neutralize at a 1:10 dilution. However, deletion of residues 91 to 129 from L2 abolishes the infectivity of BPV1, but not their binding to the cell surface. In summary, L2 residues 91 to 129 contain epitopes displayed on the virion surface and are required for infection, but not virion binding to the cell surface. Upon the binding of papillomavirus to the cell surface, residues 13 to 31 of L2 interact with a widely expressed, trypsin- and heparinase-resistant cell surface molecule and facilitate infection.     

Human papillomavirus type 16 minor capsid protein l2 N-terminal region containing a common neutralization epitope binds to the cell surface and enters the cytoplasm

The first step of papillomavirus infection is believed to be binding of major capsid protein L1 to the cell surface without involvement of minor capsid protein L2, but the viral infectivity can be neutralized either by anti-L1 or anti-L2 antibody. To understand the role of L2 in human papillomavirus (HPV) infection, we examined a segment of HPV type 16 (HPV16) L2, which contains a neutralization epitope common to HPV6, for its involvement in adsorption and penetration of the capsids. Preincubation of monkey COS-1 cells with a synthetic peptide having amino acids (aa) 108 to 120 of HPV16 L2 reduced the susceptibility of COS-1 cells to infection with HPV16 pseudovirions. Confocal microscopy showed that the green fluorescence protein (GFP) fused with the L2 peptide was found to bind to the surface of a HeLa cell, an HPV18-positive human cancer cell line, at 4 degrees C and to enter the cytoplasm after subsequent incubation at 37 degrees C. Flow cytometry showed that fused GFP did not bind to HeLa cells that had been treated with trypsin. Besides COS-1 and HeLa cells, some human and rodent cell lines were detected by flow cytometry to be susceptible to binding with fused GFP, showing a tendency of epithelial cells toward higher susceptibility. Substitutions at aa 108 to 111 inhibited fused GFP from binding to HeLa cells and reduced the infectivity in COS-1 cells of the in vitro-constructed pseudovirions. The results suggest that L2 plays an important role in enhancing HPV infection through interaction between the N-terminal region and a cellular surface protein, facilitating penetration of the virions and determining part of the tropism of HPVs.     

A pan-HPV vaccine based on bacteriophage PP7 VLPs displaying broadly cross-neutralizing epitopes from the HPV minor capsid protein, L2

Background

Current human papillomavirus (HPV) vaccines that are based on virus-like particles (VLPs) of the major capsid protein L1 largely elicit HPV type-specific antibody responses. In contrast, immunization with the HPV minor capsid protein L2 elicits antibodies that are broadly cross-neutralizing, suggesting that a vaccine targeting L2 could provide more comprehensive protection against infection by diverse HPV types. However, L2-based immunogens typically elicit much lower neutralizing antibody titers than L1 VLPs. We previously showed that a conserved broadly neutralizing epitope near the N-terminus of L2 is highly immunogenic when displayed on the surface of VLPs derived from the bacteriophage PP7. Here, we report the development of a panel of PP7 VLP-based vaccines targeting L2 that protect mice from infection with carcinogenic and non-carcinogenic HPV types that infect the genital tract and skin.

Methodology/Principal Findings

L2 peptides from eight different HPV types were displayed on the surface of PP7 bacteriophage VLPs. These recombinant L2 VLPs, both individually and in combination, elicited high-titer anti-L2 IgG serum antibodies. Immunized mice were protected from high dose infection with HPV pseudovirus (PsV) encapsidating a luciferase reporter. Mice immunized with 16L2 PP7 VLPs or 18L2 PP7 VLPs were nearly completely protected from both PsV16 and PsV18 challenge. Mice immunized with the mixture of eight L2 VLPs were strongly protected from genital challenge with PsVs representing eight diverse HPV types and cutaneous challenge with HPV5 PsV.

Conclusion/Significance

VLP-display of a cross-neutralizing HPV L2 epitope is an effective approach for inducing high-titer protective neutralizing antibodies and is capable of offering protection from a spectrum of HPVs associated with cervical cancer as well as genital and cutaneous warts.     

In vitro generation and type-specific neutralization of a human papillomavirus type 16 virion pseudotype.

We report a system for generating infectious papillomaviruses in vitro that facilitates the analysis of papillomavirus assembly, infectivity, and serologic relatedness. Cultured hamster BPHE-1 cells harboring autonomously replicating bovine papillomavirus type 1 (BPV1) genomes were infected with recombinant Semliki Forest viruses that express the structural proteins of BPV1. When plated on C127 cells, extracts from cells expressing L1 and L2 together induced numerous transformed foci that could be specifically prevented by BPV neutralizing antibodies, demonstrating that BPV infection was responsible for the focal transformation. Extracts from BPHE-1 cells expressing L1 or L2 separately were not infectious. Although Semliki Forest virus-expressed L1 self-assembled into virus-like particles (VLPs), viral DNA was detected in particles only when L2 was coexpressed with L1, indicating that genome encapsidation requires L2. Expression of human papillomavirus type 16 (HPV16) L1 and L2 together in BPHE-1 cells also yielded infectious virus. These pseudotyped virions were neutralized by antiserum to HPV16 VLPs derived from European (114/K) or African (Z-1194) HPV16 variants but not by antisera to BPV VLPs, to a poorly assembling mutant HPV16 L1 protein, or to VLPs of closely related genital HPV types. Extracts from BPHE-1 cells coexpressing BPV L1 and HPV16 L2 or HPV16 L1 and BPV L2 were not infectious. We conclude that (i) mouse C127 cells express the cell surface receptor for HPV16 and are able to uncoat HPV16 capsids; (ii) if a papillomavirus DNA packaging signal exists, then it is conserved between the BPV and HPV16 genomes; (iii) functional L1-L2 interaction exhibits type specificity; and (iv) protection by HPV virus-like particle vaccines is likely to be type specific.     

Increasing the expression levels of papillomavirus major capsid protein in Escherichia coli by N-terminal deletion

The major capsid protein L1 of human papillomavirus (HPV) contains the immunodominant neutralization epitopes of the virus and can auto-assembles to form virus-like particles (VLPs). Therefore, HPV L1 capsid proteins have been well investigated as potential vaccine candidates. To express large quantities of human papillomavirus type 16 (HPV-16) L1 in Escherichia coli (E. coli), The HPV-16 L1 gene was cloned into pGEX-4T-1, resulting in only low expression levels of HPV-16 L1 in E. coli. The first 129 nucleotides of the 5' end of the L1 gene, which contains the major inhibitory RNA element, were then deleted. The deletion RNA was efficiently translated, resulting in about 2-fold higher L1 accumulation in E. coli. The N-terminal amino-acid deletion did not affect the ability of L1 to auto-assemble in E. coli and form small VLPs.     

A protective and broadly cross-neutralizing epitope of human papillomavirus L2

We generated a monoclonal antibody, RG-1, that binds to highly conserved L2 residues 17 to 36 and neutralizes human papillomavirus 16 (HPV16) and HPV18. Passive immunotherapy with RG-1 was protective in mice. Antiserum to the HPV16 L2 peptide comprising residues 17 to 36 (peptide 17-36) neutralized pseudoviruses HPV5, HPV6, HPV16, HPV 18, HPV31, HPV 45, HPV 52, HPV 58, bovine papillomavirus 1, and HPV11 native virions. Depletion of HPV16 L2 peptide 17-36-reactive antibodies from cross-neutralizing rabbit and human L2-specific sera abolished cross-neutralization and drastically reduced neutralization of the cognate type. This cross-neutralization of diverse HPVs associated with cervical cancer, genital warts, and epidermodysplasia verruciformis suggests the possibility of a broadly protective, peptide-based vaccine.     

VLPs Displaying a Single L2 Epitope Induce Broadly Cross-Neutralizing Antibodies against Human Papillomavirus

Background

Virus-like Particles (VLPs) display can be used to increase the immunogenicity of heterologous antigens. Here, we report the use of a bacteriophage MS2-based VLP display platform to develop a monovalent vaccine targeting a broadly neutralizing epitope in the minor capsid protein human papillomavirus (HPV) that provides broad protection from diverse HPV types in a mouse pseudovirus infection model.

Methodology/Principal Findings

Peptides spanning a previously described cross-neutralizing epitope from HPV type 16 were genetically inserted at the N-terminus of MS2 bacteriophage coat protein. Three of the four recombinant L2-coat proteins assembled into VLPs. L2-VLPs elicited high-titer anti-L2 antibodies in mice, similar to recombinant VLPs that we had previously made in which the L2 peptide was displayed on a surface-exposed loop on VLPs of a related bacteriophage, PP7. Somewhat surprisingly, L2-MS2 VLPs elicited antibodies that were much more broadly cross-reactive with L2 peptides from diverse HPV isolates than L2-PP7 VLPs. Similarly, mice immunized with L2-MS2 VLPs were protected from genital and cutaneous infection by highly diverse HPV pseudovirus types.

Conclusion/Significance

We show that peptides can be displayed in a highly immunogenic fashion at the N-terminus of MS2 coat protein VLPs. A VLP-based vaccine targeting HPV L2 elicits broadly cross-reactive and cross-protective antibodies to heterologous HPV types. L2-VLPs could serve as the basis of a broadly protective second generation HPV vaccine.     

Nuclear import strategies of high risk HPV16 L1 major capsid protein

During the late phase of human papillomavirus (HPV) infection, the L1 major capsid proteins enter the nuclei of host epithelial cells and, together with the L2 minor capsid proteins, assemble the replicated viral DNA into virions. We investigated the nuclear import of the L1 major capsid protein of high risk HPV16. When digitonin-permeabilized HeLa cells were incubated with HPV16 L1 capsomeres, the L1 protein was imported into the nucleus in a receptor-mediated manner. HPV16 L1 capsomeres formed complexes with Kap alpha2beta1 heterodimers via interaction with Kap alpha2. Accordingly, nuclear import of HPV16 L1 capsomeres was mediated by Kap alpha2beta1 heterodimers, required RanGDP and free GTP, and was independent of GTP hydrolysis. Remarkably, HPV16 L1 capsomeres also interacted with Kap beta2 and binding of RanGTP to Kap beta2 did not dissociate the HPV16 L1.Kap beta2 complex. Significantly, HPV16 L1 capsomeres inhibited the nuclear import of Kap beta2 and of a Kap beta2-specific M9-containing cargo. These data suggest that, during the productive stage of infection, while the HPV16 L1 major capsid protein enters the nucleus via the Kap alpha2beta1-mediated pathway to assemble the virions, it also inhibits the Kap beta2-mediated nuclear import of host hnRNP A1 protein and, in this way, favors virion formation.     

Polyglutamine aggregation behavior in vitro supports a recruitment mechanism of cytotoxicity

The L1 major capsid proteins of human papillomavirus (HPV) types 11 and 16 were purified and analyzed for structural integrity and in vitro self-assembly. Proteins were expressed in Escherichia coli as glutathione-S-transferase-L1 (GST-L1) fusions and purified to near homogeneity as pentamers (equivalent to viral capsomeres), after thrombin cleavage from the GST moiety and removal of tightly associated GroEL protein. Sequences at the amino and carboxy termini contributing to formation of L1 pentamers and to in vitro capsid assembly were identified by deletion analysis. For both HPV11 and HPV16 L1, up to at least ten residues could be deleted from the amino terminus (Delta N10) and 30 residues from the carboxy terminus (Delta C30) without affecting pentamer formation. The HPV16 pentamers assembled into relatively regular, 72-pentamer shells ("virus-like particles" or VLPs) at low pH, with the exception of HPV16 L1 Delta N10, which assembled into a 12-pentamer, T=1 capsid (small VLP) under all conditions tested. The production of large quantities of assembly-competent L1, using the expression and purification protocol described here, has been useful for crystallographic analysis, and will be valuable for studies of virus-receptor interactions and potentially for vaccine design.     

Characterization of HPV16 L1 loop domains in the formation of a type-specific,conformational epitope

Background  

Virus-like particles (VLPs) formed by the human papillomavirus (HPV) L1 capsid protein are currently being tested in clinical trials as prophylactic vaccines against genital warts and cervical cancer. The efficacy of these vaccines is critically dependent upon L1 type-specific conformational epitopes. To investigate the molecular determinants of the HPV16 L1 conformational epitope recognized by monoclonal antibody 16A, we utilized a domain-swapping approach to generate a series of L1 proteins composed of a canine oral papillomavirus (COPV) L1 backbone containing different regions of HPV16 L1.     

Enhancement of vaccine potency by fusing modified LTK63 into human papillomavirus type 16 chimeric virus-like particles

To enhance the immunogenicity of human papillomavirus 16 (HPV 16) virus-like particles (VLPs), the modified adjuvant, mLTK63, was fused to the C-terminus of HPV 16 L2 protein. Coexpression of HPV 16 L1 and L2-mLTK63 proteins in insect cells led to the efficient assembly of HPV 16 L1/L2-mLTK63 chimeric VLPs (cVLPs), which combined the antigen and adjuvant as a unit. Compared with HPV 16 L1/L2 VLPs, the HPV 16 L1/L2-mLTK63 cVLPs had similar structural biology characteristics and binding activities with the cell surface receptors and HPV 16-specific neutralizing monoclonal antibodies. Intramuscular immunization of BALB/c mice with the HPV 16 L1/L2-mLTK63 cVLPs could induce higher titers of HPV 16-specific long-lasting neutralizing serum antibodies and stronger splenocyte proliferation, Th1- and Th2-type cytokines and CD4(+) Th responses than HPV 16 L1/L2 VLPs. The results suggested that it is possible to enhance the immunogenicity of HPV VLP vaccines via a strategy of fusing effective adjuvant protein into cVLPs.     

Interaction of human papillomavirus (HPV) type 16 capsid proteins with HPV DNA requires an intact L2 N-terminal sequence.

Encapsidation of papillomavirus DNA involves DNA-protein and protein-protein interactions. We sought to define the role of each human papillomavirus (HPV) capsid protein in HPV DNA encapsidation. HPV16 major (L1) and minor (L2) capsid proteins purified from recombinant vaccinia virus-infected cells were compared for their ability to bind nucleic acids. L2 protein, but not L1 protein, could bind HPV DNA. To map the DNA-binding region of L2, a series of truncated or point-mutated L2 protein open reading frames were used to show that only the N terminal of L2 was required for L2-DNA binding. This interaction depends critically on charged amino acids (Lys or Arg) in the first 12 amino acids of the N terminal of the protein. Several techniques were used to show that L2 interaction with DNA did not require specific DNA sequences. We propose that HPV L2 protein may play a major role in papillomavirus capsid assembly by introducing HPV DNA to the virus particles formed by the self assembly of the L1 major structural protein.     

Construction of prophylactic human papillomavirus type 16 L1 capsid protein vaccine delivered by live attenuated Shigella flexneri strain sh42

To express human papillomavirus （HPV） L 1 capsid protein in the recombinant strain of Shigella and study the potential of a live attenuated Shigella-based HPV prophylactic vaccine in preventing HPV infection, the icsA/virG fragment of Shigella-based prokaryotic expression plasmid pHS3199 was constructed. HPV type 16 L1 （HPV16L1） gene was inserted into plasmid pHS3199 to form the pHS3199-HPV16L1 construct, and pHS3199-HPV 16L1 was electroporated into a live attenuated Shigella strain sh42. Western blotting analysis showed that HPV 16L 1 could be expressed stably in the recombinant strain sh42-HPV 16L 1. Sereny test results were negative, which showed that the sh42-HPV16L1 lost virulence. However, the attenuated recombinant strain partially maintained the invasive property as indicated by the HeLa cell infection assay. Specific IgG, IgA antibody against HPV16L1 virus-like particles （VLPs） were detected in the sera, intestinal lavage and vaginal lavage from animals immunized by sh42-HPV 16L1. The number of antibodysecreting cells in the spleen and draining lymph nodes were increased significantly compared with the control group. Sera from immunized animals inhibited mufine hemagglutination induced by HPV 16L1 VLPs, which indicated that the candidate vaccine could stimulate an efficient immune response in guinea pig＇s mucosal sites. This may be an effective strategy for the development of an HPV prophylactic oral vaccine.     

Production of human papillomavirus 6b L1 virus-like particles incorporated with enhanced green fluorescent whole protein in silkworm larvae

Using human papillomavirus (HPV) as a subunit vaccine and its manipulation of surface loops is current trending research. Since the atomic model of L1 protein conformations were deciphered, their manipulations of epitopes bring multivalent vaccines. Here, in the present study, we have manipulated antigenic loops of HPV 6b L1 capsid proteins in the amino acid regions 174 ～ 175 (L1:174EGFP) and 348 ～ 349 (L1:348EGFP) with whole enhanced green fluorescent protein(EGFP), expressed in the silkworm larva using Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid technology. The expressed proteins were partially purified using sucrose density-gradient centrifugation and size-exclusion chromatography (SEC). The display of EGFP in virus-like particles (VLPs) was confirmed by immuno-fluorescence microscopy, Western blots and immune-transmission electron microscopy (immuno-TEM). There was higher expression of EGFP incorporated L1:174EGFP than L1:348EGFP. Hydrodynamic diameter of VLPs was corroborated by dynamic light scattering, confirming the size of expected range of around 160 nm and substantiating the incorporation of EGFP. From immuno-TEM, each L1:EGFP VLP formed small particles, suggesting that small particles of L1:EGFP fusion protein were aggregated. Our study illustrates that incorporation of whole protein can efficiently form chimeric VLPs, without hindering the conformation. HPV L1 protein accommodated a whole protein on its antigenic loop as a small particle, but an inserted whole protein was unstable.     

L1 interaction domains of papillomavirus l2 necessary for viral genome encapsidation

BPHE-1 cells, which harbor 50 to 200 viral episomes, encapsidate viral genome and generate infectious bovine papillomavirus type 1 (BPV1) upon coexpression of capsid proteins L1 and L2 of BPV1, but not coexpression of BPV1 L1 and human papillomavirus type 16 (HPV16) L2. BPV1 L2 bound in vitro via its C-terminal 85 residues to purified L1 capsomers, but not with intact L1 virus-like particles in vitro. However, when the efficiency of BPV1 L1 coimmunoprecipitation with a series of BPV1 L2 deletion mutants was examined in vivo, the results suggested that residues 129 to 246 and 384 to 460 contain independent L1 interaction domains. An L2 mutant lacking the C-terminal L1 interaction domain was impaired for encapsidation of the viral genome. Coexpression of BPV1 L1 and a chimeric L2 protein composed of HPV16 L2 residues 1 to 98 fused to BPV1 L2 residues 99 to 469 generated infectious virions. However, inefficient encapsidation was seen when L1 was coexpressed with either BPV1 L2 with residues 91 to 246 deleted or with BPV1 L2 with residues 1 to 225 replaced with HPV16 L2. Impaired genome encapsidation did not correlate closely with impairment of the L2 proteins either to localize to promyelocytic leukemia oncogenic domains (PODs) or to induce localization of L1 or E2 to PODs. We conclude that the L1-binding domain located near the C terminus of L2 may bind L1 prior to completion of capsid assembly, and that both L1-binding domains of L2 are required for efficient encapsidation of the viral genome.     

大肠杆菌来源的人乳头瘤病毒11型病毒样颗粒的制备及其免疫原性

摘要：【目的】 利用大肠杆菌表达系统制备人乳头瘤病毒11型病毒样颗粒（HPV11 VLPs）,并对其免疫原性和所诱导中和抗体的型交叉反应性进行研究。 【方法】 在大肠杆菌ER2566中非融合表达HPV11-L1蛋白,并通过离子交换层析,疏水相互作用层析其进行纯化。纯化后的HPV11-L1经体外组装形成病毒样颗粒,通过动态光散射,透射电镜检测其形态,并通过多种HPV型别假病毒中和实验评价HPV11 VLPs的免疫原性及型交叉反应性。 【结果】 HPV11-L1蛋白在大肠杆菌中可以以可溶形式表达。经过硫酸铵沉     

A Vaccine of L2 Epitope Repeats Fused with a Modified IgG1 Fc Induced Cross-Neutralizing Antibodies and Protective Immunity against Divergent Human Papillomavirus Types

Current human papillomavirus (HPV) major capsid protein L1 virus-like particles (VLPs)-based vaccines in clinic induce strong HPV type-specific neutralizing antibody responses. To develop pan-HPV vaccines, here, we show that the fusion protein E3R4 consisting of three repeats of HPV16 L2 aa 17–36 epitope (E3) and a modified human IgG1 Fc scaffold (R4) induces cross-neutralizing antibodies and protective immunity against divergent HPV types. E3R4 was expressed as a secreted protein in baculovirus expression system and could be simply purified by one step Protein A affinity chromatography with the purity above 90%. Vaccination of E3R4 formulated with Freunds adjuvant not only induced cross-neutralizing antibodies against HPV pseudovirus types 16, 18, 45, 52, 58, 6, 11 and 5 in mice, but also protected mice against vaginal challenges with HPV pseudovirus types 16, 45, 52, 58, 11 and 5 for at least eleven months after the first immunization. Moreover, vaccination of E3R4 formulated with FDA approved adjuvant alum plus monophosphoryl lipid A also induced cross-neutralizing antibodies against HPV types 16, 18 and 6 in rabbits. Thus, our results demonstrate that delivery of L2 antigen as a modified Fc-fusion protein may facilitate pan-HPV vaccine development.     

Expression of human papillomavirus type 11 L1 protein in insect cells: in vivo and in vitro assembly of viruslike particles.

The L1 coat protein of human papillomavirus type 11 (HPV-11) was expressed in Sf-9 insect cells with the recombinant baculovirus vector Ac11L1. Viruslike particles (VLPs) were identified by electron microscopy in the nucleus and cytoplasm of Sf-9 cells infected with Ac11L1. The L1 protein was purified from Ac11L1-infected insect cells. The purified protein spontaneously assembled in vitro into various aggregates, including particles appearing similar to empty virions. Reaction of VLP-containing insect cell extracts with antisera directed against either denatured or nondenatured capsid epitopes in Western blot (immunoblot) and immuno-dot blot assays suggested that conformational epitopes present in native HPV-11 infectious virions were also present on the baculovirus-produced HPV-11 VLPs. Immuno-dot blot assays using human sera obtained from individuals with biopsy-proven condyloma acuminatum correlated closely with results previously obtained in HPV-11 whole virus particle-based enzyme-linked immunosorbent assays. These morphologic and immunologic similarities to native HPV-11 virions suggest that recombinant VLPs produced in the baculovirus system may be useful in seroepidemiology and pathogenesis studies of genital HPV infection and that they may also be potential candidates for vaccine development.     

Optimum conditions for production and purification of human papillomavirus type 16 L1 protein from Saccharomyces cerevisiae

Several prophylactic human papillomavirus (HPV) vaccines have been developed based on virus-like particles (VLPs) made from viral L1 proteins. A substantial number of VLPs is necessary for biochemical characterization and diagnostic test development. To establish the optimum conditions for production and purification of HPV L1 in the yeast expression system we varied the amount and nature of the carbon source and evaluated HPV 16 L1 recovery by three purification methods. Maximally threefold more HPV 16 L1 was produced with a 4% carbon source than with a 2% carbon source. In addition, the productivity of HPV 16 L1 varied by 25% depending on the combination of glucose and galactose in the 4% carbon source. We introduced an ammonium sulfate precipitation step in place of the ultracentrifugation using a sucrose cushion routinely used for HPV L1 purification, and optimized the purification by cation-exchange chromatography. Overall L1 protein recovery using the ammonium sulfate precipitation method was 30%, the highest recovery achieved so far. The purified HPV 16 L1 protein successfully self-assembled into VLPs. Purification by ammonium sulfate precipitation was maximally 15 times greater than ultracentrifugation on a sucrose cushion. We anticipate that our procedures for production and purification will reduce the cost, time and labor involved in obtaining sufficient yields of VLPs.     

Expression of human papillomavirus types 6b and 16 L1 open reading frames in Escherichia coli: detection of a 56,000-dalton polypeptide containing genus-specific (common) antigens.

The human papillomavirus (HPV) genome contains two large open reading frames (ORFs), designated L1 and L2. To characterize the antigenic properties of the L1 ORF-encoded proteins, we cloned the L1 ORFs of HPV6b and HPV16 in plasmids, and these were expressed in Escherichia coli. First, the HPV6b DNA, representing 85.2% of the L1 ORF, was cloned in pUC19 and expressed in E. coli JM83 and RB791 as a 160,000-molecular-weight (160K) fusion protein with E. coli beta-galactosidase (6bL1/beta-gal). Second, the HPV16 DNA, representing 89.8% of the L1 ORF, was cloned in pKK233-2 and expressed as a 56K protein (16L1) in strain RB791. Both the 6bL1/beta-gal and 16L1 proteins cross-reacted with anti-bovine papillomavirus type 1 (BPV1) antibody raised against disrupted BPV1 particles. An antibody raised against the 6bL1/beta-gal fusion protein reacted with the 16L1 protein and also with native papillomavirus antigens in human genital condyloma and bovine fibropapilloma tissues, as determined by biotin-streptavidin staining. Furthermore, the anti-6bL1/beta-gal antibody recognized a 54K protein which seemed to be a major capsid protein of BPV1 and also a 56K protein of biopsies harboring HPV6 or HPV11. From these results we concluded that the papillomavirus L1 gene product contains genus-specific (common) antigens and that the HPV6 and HPV11 L1 genes specify the 56K capsid protein.