Brucella spp. lumazine synthase as a bovine rotavirus antigen delivery system

Molecular Design of Encapsulin Protein Nanoparticles to Display Rotavirus Antigens for Enhancing Immunogenicity

Rotavirus considerably threatens global health, particularly for children <5 years. Current, licensed oral attenuated vaccine formulations have limitations including insufficient efficacy in children in low- and middle-income countries, warranting urgent development of novel vaccines with improved efficacy and safety profiles. Herein, we present a novel approach utilizing an encapsulin (ENC) nanoparticle (NP)-based non-replicating rotavirus vaccine. ENC, originating from bacteria, offers a self-assembling scaffold that displays rotavirus VP8* antigens on its surface. To enhance the correct folding and soluble expression of monomeric antigens and their subsequent assembly into NP, we adopted an RNA-interacting domain (RID) of mammalian transfer RNA synthetase as an expression tag fused to the N-terminus of the ENC-VP8* fusion protein. Using the RID-ENC-VP8* tripartite modular design, insertion of linkers of appropriate length and sequence and the universal T cell epitope P2 remarkably improved the production yield and immunogenicity. Cleavage of the RID rendered a homogenous assembly of ENC-P2-VP8* into protein NPs. Immunization with ENC-P2-VP8* induced markedly higher levels of VP8*-specific antibodies and virus neutralization titers in mice than those induced by P2-VP8* without ENC. Altogether, these results highlight the potential of the designed ENC NP-based rotavirus vaccine as an effective strategy against rotavirus disease to address global health challenges.

Improvement of Cellulomonas fimi endoglucanase CenA by multienzymatic display on a decameric structural scaffold

The development of multifunctional particles using polymeric scaffolds is an emerging technology for many nanobiotechnological applications. Here we present a system for the production of multifunctional complexes, based on the high affinity non-covalent interaction of cohesin and dockerin modules complementary fused to decameric Brucella abortus lumazine synthase (BLS) subunits, and selected target proteins, respectively. The cohesin-BLS scaffold was solubly expressed in high yield in Escherichia coli, and revealed a high thermostability. The production of multienzymatic particles using this system was evaluated using the catalytic domain of Cellulomonas fimi endoglucanase CenA recombinantly fused to a dockerin module. Coupling of the enzyme to the scaffold was highly efficient and occurred with the expected stoichiometry. The decavalent enzymatic complexes obtained showed higher cellulolytic activity and association to the substrate compared to equivalent amounts of the free enzyme. This phenomenon was dependent on the multiplicity and proximity of the enzymes coupled to the scaffold, and was attributed to an avidity effect in the polyvalent enzyme interaction with the substrate. Our results highlight the usefulness of the scaffold presented in this work for the development of multifunctional particles, and the improvement of lignocellulose degradation among other applications. KEY POINTS: • New system for multifunctional particle production using the BLS scaffold • Higher cellulolytic activity of polyvalent endoglucanase compared to the free enzyme • Amount of enzyme associated to cellulose is higher for the polyvalent endoglucanase.

Asymmetric bifunctional protein nanoparticles through redesign of self-assembly

Engineering oligomeric protein self-assembly is an attractive approach to fabricate nanostructures with well-defined geometries, stoichiometry and functions. The homodecamer Brucella Lumazine Synthase (BLS) is a highly stable and immunogenic protein nanoparticle (PNP). Here, we engineered the BLS protein scaffold to display two functions in spatially opposite regions of its structure yielding a Janus-like nanoparticle. An in silico analysis of the BLS head-to-head dimer of homopentamers shows major inter-pentameric interactions located in the equatorial interface. Based on this analysis, two BLS protomer variants were designed to interrupt pentamer self-dimerization and promote heteropentameric dimers. This strategy enabled us to generate a decameric particle with two distinct sides formed by two independent pentamers. The versatility of this new self-assembly nanofabrication strategy is illustrated with two example applications. First, a bifunctional BLS bearing Alexa Fluor 488 fluorophores on one side and sialic acid binding domains on the other side was used for labelling murine and human cells and analyzed by flow cytometry and confocal microscopy. Second, multichromophoric FRET nanoparticles were fabricated and characterized at the single molecule level, showing discrete energy transfer events. The engineered BLS variants constitute a general platform for displaying two functions in a controlled manner within the same PNP with potential applications in various areas such as biomedicine, biotechnology and nanotechnology.

Characterization of folding-sensitive nanobodies as tools to study the expression and quality of protein particle immunogens

Vaccination is as one of the most beneficial biopharmaceutical interventions against pathogens due to its ability to induce adaptive immunity through targeted activation of the immune system. Each vaccine needs a tailor-made set of tests in order to monitor its quality throughout the development and manufacturing. The analysis of the conformational state of protein nanoparticles is one of the key steps in vaccine quality control. The enzyme lumazine synthase from Brucella spp. (BLS) acts as a potent oral and systemic immunogen. BLS has been used as a carrier of foreign peptides, protein domains and whole proteins, serving as a versatile platform for vaccine engineering purposes. Here, we show the generation and characterization of four families of nanobodies (Nbs) which only recognize BLS in its native conformational state and that bind to its active site. The present results support the use of conformation-sensitive Nbs as molecular probes during the development and production of vaccines based on the BLS platform. Finally, we propose Nbs as useful molecular tools targeting other protein scaffolds with potential applications in nano-and biotechnology.

Tailoring lumazine synthase assemblies for bionanotechnology

The cage-forming protein lumazine synthase is readily modified, evolved and assembled with other components.

Characterization of structural and immunological properties of a fusion protein between flagellin from Salmonella and lumazine synthase from Brucella

Aiming to combine the flexibility of Brucella lumazine synthase (BLS) to adapt different protein domains in a decameric structure and the capacity of BLS and flagellin to enhance the immunogenicity of peptides that are linked to their structure, we generated a chimeric protein (BLS-FliC131) by fusing flagellin from Salmonella in the N-termini of BLS. The obtained protein was recognized by anti-flagellin and anti-BLS antibodies, keeping the oligomerization capacity of BLS, without affecting the folding of the monomeric protein components determined by circular dichroism. Furthermore, the thermal stability of each fusion partner is conserved, indicating that the interactions that participate in its folding are not affected by the genetic fusion. Besides, either in vitro or in vivo using TLR5-deficient animals we could determine that BLS-FliC131 retains the capacity of triggering TLR5. The humoral response against BLS elicited by BLS-FliC131 was stronger than the one elicited by equimolar amounts of BLS + FliC. Since BLS scaffold allows the generation of hetero-decameric structures, we expect that flagellin oligomerization on this protein scaffold will generate a new vaccine platform with enhanced capacity to activate immune responses.

Integrated molecular and bioprocess engineering for bacterially produced immunogenic modular virus-like particle vaccine displaying 18 kDa rotavirus antigen

A high global burden of rotavirus disease and the unresolved challenges with the marketed rotavirus vaccines, particularly in the developing world, have ignited efforts to develop virus-like particle (VLP) vaccines for rotavirus. While rotavirus-like particles comprising multiple viral proteins can be difficult to process, modular VLPs presenting rotavirus antigenic modules are promising alternatives in reducing process complexity and cost. In this study, integrated molecular and bioprocess engineering approaches were used to simplify the production of modular murine polyomavirus capsomeres and VLPs presenting a rotavirus 18 kDa VP8* antigen. A single construct was generated for dual expression of non-tagged murine polyomavirus capsid protein VP1 and modular VP1 inserted with VP8*, for co-expression in Escherichia coli. Co-expressed proteins assembled into pentameric capsomeres in E. coli. A selective salting-out precipitation and a polishing size exclusion chromatography step allowed the recovery of stable modular capsomeres from cell lysates at high purity, and modular capsomeres were successfully translated into modular VLPs when assembled in vitro. Immunogenicity study in mice showed that modular capsomeres and VLPs induced high levels of VP8*-specific antibodies. Our results demonstrate that a multipronged synthetic biology approach combining molecular and bioprocess engineering enabled simple and low-cost production of highly immunogenic modular capsomeres and VLPs presenting conformational VP8* antigenic modules. This strategy potentially provides a cost-effective production route for modular capsomere and VLP vaccines against rotavirus, highly suitable to manufacturing economics for the developing world. Biotechnol. Bioeng. 2017;114: 397-406. © 2016 Wiley Periodicals, Inc.

Immunogenicity Analysis of a Novel Subunit Vaccine Candidate Molecule-Recombinant L7/L12 Ribosomal Protein of Brucella suis

Brucella was an intracellular parasite, which could infect special livestock and humans. After infected by Brucella, livestock's reproductive system could be affected and destroyed resulting in huge economic losses. More seriously, it could be contagious from livestock to humans. So far, there is no available vaccine which is safe enough for humans. On this point, subunit vaccine has become the new breakthrough of conquering brucellosis. In this study, Brucella rL7/L12-BLS fusion protein was used as an antigen to immunize rabbits to detect the immunogenicity. The results of antibody level testing assay of rabbit antiserum indicated rL7/L12-BLS fusion protein could elicit rabbits to produce high-level IgG. And gamma interferon (IFN-γ) concentrations in rabbit antiserum were obviously up-regulated in both the rL7/L12 group and rL7/L12-BLS group. Besides, the results of quantitative real-time PCR (qRT-PCR) showed the IFN-γ gene's expression levels of both the rL7/L12 group and rL7/L12-BLS group were obviously up-regulated. All these results suggested Brucella L7/L12 protein was an ideal subunit vaccine candidate and possessed good immunogenicity. And Brucella lumazine synthase (BLS) molecule was a favorable transport vector for antigenic protein.

Expression of the Multimeric and Highly Immunogenic Brucella spp. Lumazine Synthase Fused to Bovine Rotavirus VP8d as a Scaffold for Antigen Production in Tobacco Chloroplasts

Lumazine synthase from Brucella spp. (BLS) is a highly immunogenic decameric protein which can accommodate foreign polypeptides or protein domains fused to its N-termini, markedly increasing their immunogenicity. The inner core domain (VP8d) of VP8 spike protein from bovine rotavirus is responsible for viral adhesion to sialic acid residues and infection. It also displays neutralizing epitopes, making it a good candidate for vaccination. In this work, the BLS scaffold was assessed for the first time in plants for recombinant vaccine development by N-terminally fusing BLS to VP8d and expressing the resulting fusion (BLSVP8d) in tobacco chloroplasts. Transplastomic plants were obtained and characterized by Southern, northern and western blot. BLSVP8d was highly expressed, representing 40% of total soluble protein (4.85 mg/g fresh tissue). BLSVP8d remained soluble and stable during all stages of plant development and even in lyophilized leaves stored at room temperature. Soluble protein extracts from fresh and lyophilized leaves were able to induce specific neutralizing IgY antibodies in a laying hen model. This work presents BLS as an interesting platform for highly immunogenic injectable, or even oral, subunit vaccines. Lyophilization of transplastomic leaves expressing stable antigenic fusions to BLS would further reduce costs and simplify downstream processing, purification and storage, allowing for more practical vaccines.

Plant-produced viral bovine vaccines: what happened during the last 10 years?

Vaccination has proved to be an efficient strategy to deal with viral infections in both human and animal species. However, protection of cattle against viral infections is still a major concern in veterinary science. During the last two decades, the development of efficient plant-based expression strategies for recombinant proteins prompted the application of this methodology for veterinary vaccine purposes. The main goals of viral bovine vaccines are to improve the health and welfare of cattle and increase the production of livestock, in a cost-effective manner. This review explores some of the more prominent recent advances in plant-made viral bovine vaccines against foot-and-mouth disease virus (FMDV), bovine rotavirus (BRV), bovine viral diarrhoea virus (BVDV), bluetongue virus (BTV) and bovine papillomavirus (BPV), some of which are considered to be the most important viral causative agents of economic loss in cattle production.

Recent advances in riboflavin biosynthesis

Riboflavin is biosynthesized from GTP and ribulose 5-phosphate. Whereas the early reactions conducing to 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione 5'-phosphate show significant taxonomic variation, the subsequent reaction steps are universal in all taxonomic kingdoms. With the exception of a hitherto elusive phosphatase, all enzymes of the pathway have been characterized in some detail at the structural and mechanistic level. Some of the pathway enzymes (GTP cycloyhdrolase II, 3,4-dihydroxy-2-butanone 4-phosphate synthase, riboflavin synthase) have exceptionally complex reaction mechanisms. The commercial production of the vitamin is now entirely based on highly productive fermentation processes. Due to their absence in animals, the pathway enzymes are potential targets for the development of novel anti-infective drugs.

Immunization with a chimera consisting of the B subunit of Shiga toxin type 2 and brucella lumazine synthase confers total protection against Shiga toxins in mice

The striking feature of enterohemorrhagic Escherichia coli (EHEC) infections is the production of Shiga toxins (Stx) implicated in the development of the life-threatening hemolytic uremic syndrome. Despite the magnitude of the social impact of EHEC infections, no licensed vaccine or effective therapy is available for human use. One of the biggest challenges is to develop an effective and safe immunogen to ensure nontoxicity, as well as a strong input to the immune system to induce long-lasting, high-affinity Abs with anti-Stx-neutralizing capacity. The enzyme lumazine synthase from Brucella spp. (BLS) is a highly stable dimer of pentamers and a scaffold with enormous plasticity on which to display foreign Ags. Taking into account the advantages of BLS and the potential capacity of the B subunit of Stx2 to induce Abs that prevent Stx2 toxicity by blocking its entrance into the host cells, we engineered a new immunogen by inserting the B subunit of Stx2 at the amino termini of BLS. The resulting chimera demonstrated a strong capacity to induce a long-lasting humoral immune response in mice. The chimera induced Abs with high neutralizing capacity for Stx2 and its variants. Moreover, immunized mice were completely protected against i.v. Stx2 challenge, and weaned mice receiving an oral challenge with EHEC were completely protected by the transference of immune sera. We conclude that this novel immunogen represents a promising candidate for vaccine or Ab development with preventive or therapeutic ends, for use in hemolytic uremic syndrome-endemic areas or during future outbreaks caused by pathogenic strains of Stx-producing E. coli.

Equine rotaviruses--current understanding and continuing challenges

Equine rotaviruses were first detected in foals over 30 years ago and remain a major cause of infectious diarrhoea in foals. During this time, there has been substantial progress in the development of sensitive methods to detect rotaviruses in foals, enabling surveillance of the genotypes present in various horse populations. However, there has been limited epidemiological investigation into the significance of these circulating genotypes, their correlation with disease and the use of vaccination in these animal populations. Our knowledge of the pathogenesis of rotavirus infection in foals is based on a limited number of studies on a small number of foals and, therefore, most of our understanding in this area has been extrapolated from studies in other species. Questions such as the concentrations of rotavirus particles shed in the faeces of infected foals, both with and without diarrhoea, and factors determining the presence or absence of clinical disease remain to be investigated, as does the relative and absolute efficacy of currently available vaccines. The answer to these questions may help direct research into the development of more effective control measures.

A polymeric protein induces specific cytotoxicity in a TLR4 dependent manner in the absence of adjuvants

Lumazine synthase from Brucella spp. (BLS) is a highly immunogenic decameric protein. It is possible to insert foreign peptides or proteins at its ten-amino acid termini. These chimeras elicit systemic and oral immunity without adjuvants, which are commonly needed in the formulation of subunit-based vaccines. Here, we show that BLS induces the cross presentation of a covalently attached peptide OVA_257–264 and a specific cytotoxic response to this peptide in the absence of adjuvants. Unlike other subunit-based vaccines, this chimera induces rapid activation of CTLs and a specific cytotoxic response, making this polymeric protein an ideal antigen carrier for vaccine development. Adoptive transfer of transgenic OT-I T cells revealed efficient cross presentation of BLS-OVA_257–264in vivo. BLS-OVA_257–264 immunization induced the proliferation of OVA_257–264-specific CD8+ lymphocytes and also increased the percentage of OVA_257–264-specific CD8+ cells expressing the early activation marker CD69; after 5 days, the percentage of OVA_257–264-specific CD8+ cells expressing high levels of CD44 increased. This cell subpopulation showed decreased expression of IL-7Rα, indicating that BLS-OVA_257–264 induced the generation of CD8+ effector cells. BLS-OVA_257–264 was cross presented in vitro independently of the presence of a functional TLR4 in the DCs. Finally, we show that immunization of wild type mice with the chimera BLS-OVA_257–264 without adjuvants induced a strong OVA_257–264-specific effector cytotoxic response. This cytotoxicity is dependent on TLR4 as is not induced in mice lacking a functional receptor. These data show that TLR4 signaling is necesary for the induction of a cytotoxic response but not for antigen cross presentation.

Construction and characterization of human rotavirus recombinant VP8* subunit parenteral vaccine candidates

Two currently licensed live oral rotavirus vaccines (Rotarix® and RotaTeq®) are highly efficacious against severe rotavirus diarrhea. However, the efficacy of such vaccines in selected low-income African and Asian countries is much lower than that in middle or high-income countries. Additionally, these two vaccines have recently been associated with rare case of intussusception in vaccinated infants. We developed a novel recombinant subunit parenteral rotavirus vaccine which may be more effective in low-income countries and also avert the potential problem of intussusception. Truncated recombinant VP8* (ΔVP8*) protein of human rotavirus strain Wa P[8], DS-1 P[4] or 1076 P[6] expressed in Escherichia coli was highly soluble and was generated in high yield. Guinea pigs hyperimmunized intramuscularly with each of the ΔVP8* proteins (i.e., P[8], P[4] or P[6]) developed high levels of homotypic as well as variable levels of heterotypic neutralizing antibodies. Moreover, the selected ΔVP8* proteins when administered to mice at a clinically relevant dosage, route and schedule, elicited high levels of serum anti-VP8* IgG and/or neutralizing antibodies. Our data indicated that the ΔVP8* proteins may be a plausible additional candidate as new parenteral rotavirus vaccines.

Polymeric Display of Proteins through High Affinity Leucine Zipper Peptide Adaptors

The polymeric display of proteins is a method that could be used to increase the immunogenicity of antigens and to enhance the interaction strength of binding domains for their target ligands through an avidity effect. However, the coupling of proteins to oligomeric scaffolds is challenging. The chemical conjugation and recombinant fusion techniques have limitations that prevent their general use. In this work we describe a simple and effective method for coupling proteins to the decameric structure of Brucella abortus Lumazine Synthase based on the use of a pair of high affinity heterodimeric coiled coil peptides complementary fused to the scaffold and the target protein. Results obtained with a series of proteins demonstrate the capability of this approach to generate polyvalent particles. Furthermore, we show that the method is able to increase the immunogenicity of antigens and produce polyfunctional particles with promising biomedical and nanotechnological applications.

VP8* antigen produced in tobacco transplastomic plants confers protection against bovine rotavirus infection in a suckling mouse model

Group A rotavirus is a major leading cause of diarrhea in mammalian species worldwide. In Argentina, bovine rotavirus (BRV) is the main cause of neonatal diarrhea in calves. VP4, one of the outermost capsid proteins, is involved in various virus functions. Rotavirus infectivity requires proteolytic cleavage of VP4, giving an N-terminal non-glycosilated sialic acid-recognizing domain (VP8*), and a C-terminal fragment (VP5*) that remains associated with the virion. VP8* subunit is the major determinant of the viral infectivity and one of the neutralizing antigens. In this work, the C486 BRV VP8* protein was produced in tobacco chloroplasts. Transplastomic plants were obtained and characterized by Southern blot, northern blot and western blot. VP8* was highly stable in the transplastomic leaves, and formed insoluble aggregates that were partially solubilized by sonication. The recombinant protein yield was 600 μg/g of fresh tissue (FT). Both the soluble and insoluble fractions of the VP8* plant extracts were able to induce a strong immune response in female mice as measured by ELISA and virus neutralization test. Most important, suckling mice born to immunized dams were protected against oral challenge with virulent rotavirus. Results presented here contribute to demonstrate the feasibility of using antigens expressed in transplastomic plants for the development of subunit vaccines.

Identification and characterization of antigenic proteins potentially expressed during the infectious process of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis causes paracoccidioidomycosis (PCM), a systemic mycosis presenting clinical manifestations ranging from mild to severe forms. A P. brasiliensis cDNA expression library was produced and screened with pooled sera from PCM patients adsorbed against antigens derived from in vitro-grown P. brasiliensis yeast cells. Sequencing DNA inserts from clones reactive with PCM patients sera indicated 35 open reading frames presenting homology to genes involved in metabolic pathways, transport, among other predicted functions. The complete cDNAs encoding aromatic-l-amino-acid decarboxylase (Pbddc), lumazine synthase (Pbls) and a homologue of the high affinity copper transporter (Pbctr3) were obtained. Recombinant proteins PbDDC and PbLS were obtained; a peptide was synthesized for PbCTR3. The proteins and the synthetic peptide were recognized by sera of patients with confirmed PCM and not by sera of healthy patients. Using the in vivo-induced antigen technology (IVIAT), we identified immunogenic proteins expressed at high levels during infection. Quantitative real time RT-PCR demonstrated high transcript levels of Pbddc, Pbls and Pbctr3 in yeast cells infecting macrophages. Transcripts in yeast cells derived from spleen and liver of infected mice were also measured by qRT-PCR. Our results suggest a putative role for the immunogenic proteins in the infectious process of P. brasiliensis.