Haloarchaeal gas vesicle nanoparticles displaying Salmonella antigens as a novel approach to vaccine development

Advances in the application of gas vesicles in medical imaging and disease treatment

The gas vesicle (GV) is like a hollow nanoparticle consisting of an internal gas and a protein shell, which mainly consists of hydrophobic gas vesicle protein A (GvpA) and GvpC attached to the surface. GVs, first discovered in cyanobacteria, are mainly produced by photosynthetic bacteria (PSB) and halophilic archaea. After being modified and engineered, GVs can be utilized as contrast agents, delivery carriers, and immunological boosters for disease prevention, diagnosis, and treatment with good results due to their tiny size, strong stability and non-toxicity advantages. Many diagnostic and therapeutic approaches based on GV are currently under development. In this review, we discuss the source, function, physical and chemical properties of GV, focus on the current application progress of GV, and put forward the possible application prospect and development direction of GV in the future.

Broadly Applicable Bispecific Linker Approach to Noncovalently Target Therapeutic Nanoparticles to Tumor Cells Expressing Carcinoembryonic Antigen

Design strategies that lead to a more focused in vivo delivery of functionalized nanoparticles (NPs) and their cargo can potentially maximize their therapeutic efficiency while reducing systemic effects, broadening their clinical applications. Here, we report the development of a noncovalent labeling approach where immunoglobulin G (IgG)-decorated NPs can be directed to a cancer cell using a simple, linear bispecific protein adaptor, termed MFE23-ZZ. MFE23-ZZ was created by fusing a single-chain fragment variable domain, termed MFE23, recognizing carcinoembryonic antigen (CEA) expressed on tumor cells, to a small protein ZZ module, which binds to the Fc fragment of IgG. As a proof of concept, monoclonal antibodies (mAbs) were generated against a NP coat protein, namely, gas vesicle protein A (GvpA) of Halobacterium salinarum gas vesicles (GVs). The surface of each GV was therapeutically derivatized with the photoreactive agent chlorin e6 (Ce6GVs) and anti-GvpA mAbs were subsequently bound to GvpA on the surface of each Ce6GV. The bispecific ligand MFE23-ZZ was then bound to mAb-decorated Ce6GVs via their Fc domain, resulting in a noncovalent tripartite complex, namely, MFE23.ZZ-2B10-Ce6GV. This complex enhanced the intracellular uptake of Ce6GVs into human CEA-expressing murine MC38 colon carcinoma cells (MC38.CEA) relative to the CEA-negative parental cell line MC38 in vitro, making them more sensitive to light-induced cell killing. These results suggest that the surface of NP can be rapidly and noncovalently functionalized to target tumor-associated antigen-expressing tumor cells using simple bispecific linkers and any IgG-labeled cargo. This noncovalent approach is readily applicable to other types of functionalized NPs.

Nanoscale contrast agents: A promising tool for ultrasound imaging and therapy

Nanoscale contrast agents have emerged as a versatile platform in the field of biomedical research, offering great potential for ultrasound imaging and therapy. Various kinds of nanoscale contrast agents have been extensively investigated in preclinical experiments to satisfy diverse biomedical applications. This paper provides a comprehensive review of the structure and composition of various nanoscale contrast agents, as well as their preparation and functionalization, encompassing both chemosynthetic and biosynthetic strategies. Subsequently, we delve into recent advances in the utilization of nanoscale contrast agents in various biomedical applications, including ultrasound molecular imaging, ultrasound-mediated drug delivery, and cell acoustic manipulation. Finally, the challenges and prospects of nanoscale contrast agents are also discussed to promote the development of this innovative nanoplatform in the field of biomedicine.

Bioactive molecules from haloarchaea: Scope and prospects for industrial and therapeutic applications

Marine environments and salty inland ecosystems encompass various environmental conditions, such as extremes of temperature, salinity, pH, pressure, altitude, dry conditions, and nutrient scarcity. The extremely halophilic archaea (also called haloarchaea) are a group of microorganisms requiring high salt concentrations (2-6 M NaCl) for optimal growth. Haloarchaea have different metabolic adaptations to withstand these extreme conditions. Among the adaptations, several vesicles, granules, primary and secondary metabolites are produced that are highly significant in biotechnology, such as carotenoids, halocins, enzymes, and granules of polyhydroxyalkanoates (PHAs). Among halophilic enzymes, reductases play a significant role in the textile industry and the degradation of hydrocarbon compounds. Enzymes like dehydrogenases, glycosyl hydrolases, lipases, esterases, and proteases can also be used in several industrial procedures. More recently, several studies stated that carotenoids, gas vacuoles, and liposomes produced by haloarchaea have specific applications in medicine and pharmacy. Additionally, the production of biodegradable and biocompatible polymers by haloarchaea to store carbon makes them potent candidates to be used as cell factories in the industrial production of bioplastics. Furthermore, some haloarchaeal species can synthesize nanoparticles during heavy metal detoxification, thus shedding light on a new approach to producing nanoparticles on a large scale. Recent studies also highlight that exopolysaccharides from haloarchaea can bind the SARS-CoV-2 spike protein. This review explores the potential of haloarchaea in the industry and biotechnology as cellular factories to upscale the production of diverse bioactive compounds.

Bioengineering of Halobacterium sp. NRC-1 gas vesicle nanoparticles with GvpC fusion protein produced in E. coli

Abstract

Gas vesicle nanoparticles (GVNPs) are hollow, buoyant prokaryotic organelles used for cell flotation. GVNPs are encoded by a large gas vesicle protein (gvp) gene cluster in the haloarchaeon, Halobacterium sp. NRC-1, including one gene, gvpC, specifying a protein bound to the surface of the nanoparticles. Genetically engineered GVNPs in the Halobacterium sp. have been produced by fusion of foreign sequences to gvpC. To improve the versatility of the GVNP platform, we developed a method for displaying exogenously produced GvpC fusion proteins on the haloarchaeal nanoparticles. The streptococcal IgG-binding protein domain was fused at or near the C-terminus of GvpC, expressed and purified from E. coli, and shown to bind to wild-type GVNPs. The two fusion proteins, GvpC3GB and GvpC4GB, without or with a highly acidic GvpC C-terminal region, were found to be able to bind nanoparticles equally well. The GVNP-bound GvpC-IgG-binding fusion protein was also capable of binding to an enzyme-linked IgG-HRP complex which retained enzyme activity, demonstrating the hybrid system capability for display and delivery of protein complexes. This is the first report demonstrating functional binding of exogenously produced GvpC fusion proteins to wild-type haloarchaeal GVNPs which significantly expands the capability of the platform to produce bioengineered nanoparticles for biomedical applications.

Key points

• Haloarchaeal gas vesicle nanoparticles (GVNPs) constitute a versatile display system.

• GvpC-streptococcal IgG-binding fusion proteins expressed in E. coli bind to GVNPs.

• IgG-binding proteins displayed on floating GVNPs bind and display IgG-HRP complex.

Graphical abstract

Archaeosomes and Gas Vesicles as Tools for Vaccine Development

Archaea are prokaryotic organisms that were classified as a new domain in 1990. Archaeal cellular components and metabolites have found various applications in the pharmaceutical industry. Some archaeal lipids can be used to produce archaeosomes, a new family of liposomes that exhibit high stability to temperatures, pH and oxidative conditions. Additionally, archaeosomes can be efficient antigen carriers and adjuvants promoting humoral and cellular immune responses. Some archaea produce gas vesicles, which are nanoparticles released by the archaea that increase the buoyancy of the cells and facilitate an upward flotation in water columns. Purified gas vesicles display a great potential for bioengineering, due to their high stability, immunostimulatory properties and uptake across cell membranes. Both archaeosomes and archaeal gas vesicles are attractive tools for the development of novel drug and vaccine carriers to control various diseases. In this review we discuss the current knowledge on production, preparation methods and potential applications of archaeosomes and gas vesicles as carriers for vaccines. We give an overview of the traditional structures of these carriers and their modifications. A comparative analysis of both vaccine delivery systems, including their advantages and limitations of their use, is provided. Gas vesicle- and archaeosome-based vaccines may be powerful next-generation tools for the prevention and treatment of a wide variety of infectious and non-infectious diseases.

Microbial gas vesicles as nanotechnology tools: exploiting intracellular organelles for translational utility in biotechnology, medicine and the environment

A range of bacteria and archaea produce gas vesicles as a means to facilitate flotation. These gas vesicles have been purified from a number of species and their applications in biotechnology and medicine are reviewed here. Halobacterium sp. NRC-1 gas vesicles have been engineered to display antigens from eukaryotic, bacterial and viral pathogens. The ability of these recombinant nanoparticles to generate an immune response has been quantified both in vitro and in vivo. These gas vesicles, along with those purified from Anabaena flos-aquae and Bacillus megaterium, have been developed as an acoustic reporter system. This system utilizes the ability of gas vesicles to retain gas within a stable, rigid structure to produce contrast upon exposure to ultrasound. The susceptibility of gas vesicles to collapse when exposed to excess pressure has also been proposed as a biocontrol mechanism to disperse cyanobacterial blooms, providing an environmental function for these structures.

Bionanotechnology for vaccine design

There have been significant advances in the design of nanostructured scaffolds for eliciting robust immune responses. One method to produce strong immune responses is to emulate the appearance of a pathogen. Since pathogens such as viruses and bacteria often display multiple copies of ligands on their surfaces, the immune system is particularly sensitive towards multivalent displays of antigens. Consequently, when designing a vaccine, it is advantageous to decorate a nanostructured surface with multiple copies of an antigen. This review highlights the design and efficacy of a diverse set of recently developed nanostructured vaccine scaffolds.

Microneedle-Assisted Skin Permeation by Nontoxic Bioengineerable Gas Vesicle Nanoparticles

Gas vesicle nanoparticles (GVNPs) are hollow, buoyant protein organelles produced by the extremophilic microbe Halobacterium sp. NRC-1 and are being developed as bioengineerable and biocompatible antigen and drug-delivery systems (DDS). Dynamic light scattering measurements of purified GVNP suspensions showed a mean diameter of 245 nm. In vitro diffusion studies using Yucatan miniature pig skin showed GVNP permeation to be enhanced after MN-treatment compared to untreated skin. GVNPs were found to be nontoxic to mammalian cells (human kidney and rat mycocardial myoblasts). These findings support the use of GVNPs as DDS for intradermal/transdermal permeation of protein- and peptide-based drugs.

Bioengineering novel floating nanoparticles for protein and drug delivery

Gas vesicle nanoparticles (GVNPs) are hollow protein nanoparticles produced by Halobacterium sp. NRC-1 which are being engineered for protein delivery. To advance the bioengineering potential of GVNPs, a strain of NRC-1 deleted for the gvpC gene (ΔgvpC) was constructed and a synthetic gene coding for Gaussia princeps luciferase was fused to an abbreviated gvpC gene on an expression plasmid. When introduced into theΔgvpC strain, an active GvpC-luciferase fusion protein bound to GVNPs resulted. These results represent both a technical improvement in the GVNP display system and its expansion for the display of active enzymes.

Immunogenicity and protective potential of a Plasmodium spp. enolase peptide displayed on archaeal gas vesicle nanoparticles

Background

Plasmodium falciparum enolase has been shown to localize on the surface of merozoites and ookinetes. Immunization of mice with recombinant Plasmodium enolase (rPfeno) showed partial protection against malaria. Anti-rPfeno antibodies inhibited growth of the parasite in in vitro cultures and blocked ookinete invasion of mosquito midgut epithelium. It is hypothesized that parasite specific moonlighting functions (e.g. host cell invasion) may map on to unique structural elements of Pfeno. Since enolases are highly conserved between the host and the parasite, a parasite-specific epitope of enolase was displayed on novel protein nanoparticles produced by a halophilic Archaeon Halobacterium sp. NRC-1 and tested their ability to protect mice against live challenge.

Methods

By genetic engineering, a Plasmodium-enolase specific peptide sequence ¹⁰⁴EWGWS¹⁰⁸ with protective antigenic potential was inserted into the Halobacterium gas vesicle protein GvpC, a protein localized on the surface of immunogenic gas vesicle nanoparticles (GVNPs). Two groups of mice were immunized with the wild type (WT) and the insert containing recombinant (Rec) GVNPs respectively. A third group of mice was kept as un-immunized control. Antibody titres were measured against three antigens (i.e. WT-GVNPs, Rec-GVNPs and rPfeno) using ELISA. The protective potential was determined by measuring percentage parasitaemia and survival after challenge with the lethal strain Plasmodium yoelii 17XL.

Results

Rec-GVNP-immunized mice showed higher antibody titres against rPfeno and Rec-GVNPs, indicating that the immunized mice had produced antibodies against the parasite enolase-specific insert sequence. Challenging the un-immunized, WT-GVNP and Rec-GVNP-immunized mice with a lethal strain of mice malarial parasite showed significantly lower parasitaemia and longer survival in the Rec-GVNP-immunized group as compared to control groups. The extent of survival advantage in the Rec-GVNP-group showed positive correlation with anti-rPfeno antibody titres while the parasitaemia showed a negative correlation. These results indicate that the parasite enolase peptide insert displayed on Halobacterium GVNPs is a good candidate as a protective antigenic epitope.

Conclusion

The work reported here showed that the parasite-specific peptide sequence is a protective antigenic epitope. Although antibody response of B-cells to the guest sequence in Rec-GVNPs was mild, significant advantage in the control of parasitaemia and survival was observed. Future efforts are needed to display multiple antigens with protective properties to improve the performance of the GVNP-based approach.

Gas Vesicle Nanoparticles for Antigen Display

Microorganisms like the halophilic archaeon Halobacterium sp. NRC-1 produce gas-filled buoyant organelles, which are easily purified as protein nanoparticles (called gas vesicles or GVNPs). GVNPs are non-toxic, exceptionally stable, bioengineerable, and self-adjuvanting. A large gene cluster encoding more than a dozen proteins has been implicated in their biogenesis. One protein, GvpC, found on the exterior surface of the nanoparticles, can accommodate insertions near the C-terminal region and results in GVNPs displaying the inserted sequences on the surface of the nanoparticles. Here, we review the current state of knowledge on GVNP structure and biogenesis as well as available studies on immunogenicity of pathogenic viral, bacterial, and eukaryotic proteins and peptides displayed on the nanoparticles. Recent improvements in genetic tools for bioengineering of GVNPs are discussed, along with future opportunities and challenges for development of vaccines and other applications.