An N-terminal extension to the hepatitis B virus core protein forms a poorly ordered trimeric spike in assembled virus-like particles

Multifaceted virus-like particles: Navigating towards broadly effective influenza A virus vaccines

The threat of influenza A virus (IAV) remains an annual health concern, as almost 500,000 people die each year due to the seasonal flu. Current flu vaccines are highly dependent on embryonated chicken eggs for production, which is time consuming and costly. These vaccines only confer moderate protections in elderly people, and they lack cross-protectivity; thereby requiring annual reformulation to ensure effectiveness against contemporary circulating strains. To address current limitations, new strategies are being sought, with great emphasis given on exploiting IAV's conserved antigens for vaccine development, and by using different vaccine technologies to enhance immunogenicity and expedite vaccine production. Among these technologies, there are growing pre-clinical and clinical studies involving virus-like particles (VLPs), as they are capable to display multiple conserved IAV antigens and augment their immune responses. In this review, we outline recent findings involving broadly effective IAV antigens and strategies to display these antigens on VLPs. Current production systems for IAV VLP vaccines are comprehensively reviewed. Pain-free methods for administration of IAV VLP vaccines through intranasal and transdermal routes, as well as the mechanisms in stimulating immune responses are discussed in detail. The future perspectives of VLPs in IAV vaccine development are discussed, particularly concerning their potentials in overcoming current immunological limitations of IAV vaccines, and their inherent advantages in exploring intranasal vaccination studies. We also propose avenues to expedite VLP vaccine production, as we envision that there will be more clinical trials involving IAV VLP vaccines, leading to commercialization of these vaccines in the near future.

Length and Charge of the N-terminus Regulate the Lifetime of the Signaling State of Photoactive Yellow Protein

Photoactive yellow protein (PYP) is one of the most extensively studied photoreceptors. Nevertheless, the role of the N-terminus in the photocycle and structural transitions is still elusive. Here, we attached additional amino acids to the N-terminus of PYP and investigated the effect of the length and charge of additional N-terminal residues using circular dichroism, two-dimensional nuclear magnetic resonance (2D-NMR), transient absorption (TA), and transient grating (TG) spectroscopic techniques. TA experiments showed that, except for negatively charged residues (5D-PYP), additional N-terminal residues of PYP generally enable faster dark recovery from the putative signaling state (pB2) to the ground state (pG). TG data showed that although the degree of structural changes can be controlled by adjusting specific amino acid residues in the extended N-terminus of N-terminal extended PYPs (NE-PYPs), the dark recovery times of wt-PYP and NE-PYPs, except for 5D-PYP, are independent of the structural differences between pG and pB2 states. These results demonstrate that the recovery time and the degree of structural change can be regulated by controlling the length and sequence of N-terminal residues of PYP. The findings in this study emphasize the need for careful attention to the remaining amino acid residues when designing recombinant proteins for genetic engineering purposes.

Virus-like nanoparticles as a theranostic platform for cancer

Virus-like nanoparticles (VLPs) are natural polymer-based nanomaterials that mimic viral structures through the hierarchical assembly of viral coat proteins, while lacking viral genomes. VLPs have received enormous attention in a wide range of nanotechnology-based medical diagnostics and therapies, including cancer therapy, imaging, and theranostics. VLPs are biocompatible and biodegradable and have a uniform structure and controllable assembly. They can encapsulate a wide range of therapeutic and diagnostic agents, and can be genetically or chemically modified. These properties have led to sophisticated multifunctional theranostic platforms. This article reviews the current progress in developing and applying engineered VLPs for molecular imaging, drug delivery, and multifunctional theranostics in cancer research.

Needle-free, spirulina-produced Plasmodium falciparum circumsporozoite vaccination provides sterile protection against pre-erythrocytic malaria in mice

Antibodies against the Plasmodium falciparum circumsporozoite protein (PfCSP) can block hepatocyte infection by sporozoites and protect against malaria. Needle-free vaccination strategies are desirable, yet most PfCSP-targeted vaccines like RTS,S require needle-based administration. Here, we evaluated the edible algae, Arthrospira platensis (commonly called 'spirulina') as a malaria vaccine platform. Spirulina were genetically engineered to express virus-like particles (VLPs) consisting of the woodchuck hepatitis B core capsid protein (WHcAg) displaying a (NANP)₁₅ PfCSP antigen on its surface. PfCSP-spirulina administered to mice intranasally followed by oral PfCSP-spirulina boosters resulted in a strong, systemic anti-PfCSP immune response that was protective against subcutaneous challenge with PfCSP-expressing P. yoelii. Unlike male mice, female mice did not require Montanide adjuvant to reach high antibody titers or protection. The successful use of spirulina as a vaccine delivery system warrants further development of spirulina-based vaccines as a useful tool in addressing malaria and other diseases of global health importance.

Hepatitis B virus Core protein nuclear interactome identifies SRSF10 as a host RNA-binding protein restricting HBV RNA production

Despite the existence of a preventive vaccine, chronic infection with Hepatitis B virus (HBV) affects more than 250 million people and represents a major global cause of hepatocellular carcinoma (HCC) worldwide. Current clinical treatments, in most of cases, do not eliminate viral genome that persists as a DNA episome in the nucleus of hepatocytes and constitutes a stable template for the continuous expression of viral genes. Several studies suggest that, among viral factors, the HBV core protein (HBc), well-known for its structural role in the cytoplasm, could have critical regulatory functions in the nucleus of infected hepatocytes. To elucidate these functions, we performed a proteomic analysis of HBc-interacting host-factors in the nucleus of differentiated HepaRG, a surrogate model of human hepatocytes. The HBc interactome was found to consist primarily of RNA-binding proteins (RBPs), which are involved in various aspects of mRNA metabolism. Among them, we focused our studies on SRSF10, a RBP that was previously shown to regulate alternative splicing (AS) in a phosphorylation-dependent manner and to control stress and DNA damage responses, as well as viral replication. Functional studies combining SRSF10 knockdown and a pharmacological inhibitor of SRSF10 phosphorylation (1C8) showed that SRSF10 behaves as a restriction factor that regulates HBV RNAs levels and that its dephosphorylated form is likely responsible for the anti-viral effect. Surprisingly, neither SRSF10 knock-down nor 1C8 treatment modified the splicing of HBV RNAs but rather modulated the level of nascent HBV RNA. Altogether, our work suggests that in the nucleus of infected cells HBc interacts with multiple RBPs that regulate viral RNA metabolism. Our identification of SRSF10 as a new anti-HBV restriction factor offers new perspectives for the development of new host-targeted antiviral strategies.

Chronic infection with Hepatitis B virus (HBV) affects more than 250 million of people world-wide and is a major global cause of liver cancer. Current treatments lead to a significant reduction of viremia in patients. However, viral clearance is rarely obtained and the persistence of the HBV genome in the hepatocyte’s nucleus generates a stable source of viral RNAs and subsequently proteins which play important roles in immune escape mechanisms and liver disease progression. Therapies aiming at efficiently and durably eliminating viral gene expression are still required. In this study, we identified the nuclear partners of the HBV Core protein (HBc) to understand how this structural protein, responsible for capsid assembly in the cytoplasm, could also regulate viral gene expression. The HBc interactome was found to consist primarily of RNA-binding proteins (RBPs). One of these RBPs, SRSF10, was demonstrated to restrict HBV RNA levels and a drug, able to alter its phosphorylation, behaved as an antiviral compound capable of reducing viral gene expression. Altogether, this study sheds new light on novel regulatory functions of HBc and provides information relevant for the development of antiviral strategies aiming at preventing viral gene expression.

Development of imaging scaffolds for cryo-electron microscopy

Following recent hardware and software developments, single particle cryo-electron microscopy (cryo-EM) has become one of the most popular structural biology tools. Many targets, such as viruses, large protein complexes and oligomeric membrane proteins, have been resolved to atomic resolution using single-particle cryo-EM, which relies on the accurate assignment of particle location and orientation from intrinsically noisy projection images. The same image processing procedures are more challenging for smaller proteins due to their lower signal-to-noise ratios. Consequently, though most cellular proteins are less than 50kDa, so far it has been possible to solve cryo-EM structures near that size range for only a few favorable cases. Here we highlight some of the challenges and recent efforts to break through this lower size limit by engineering large scaffolds to rigidly display multiple small proteins for imaging. Future design efforts are noted.

Epitope selection and their placement for increased virus neutralization in a novel vaccination strategy for porcine epidemic diarrhea virus utilizing the Hepatitis B virus core antigen

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Hepatitis B core antigen (HBcAg) protein with PEDV epitopes can assemble into virus like particles.

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Epitope placement within HBcAg can affect the immunogenicity of a vaccine.

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The YSNIGVCK antigen from PEDV has a strong correlation with virus neutralization.

Porcine epidemic diarrhea virus (PEDV) is a member of the Alphacoronaviridae genus within the Coronaviridae family. It is the causative agent of porcine epidemic diarrhea, a disease that can have mortality rates as high as 100% in suckling piglets. PEDV causes severe economic loss, and has been in existence for decades. A panzootic starting in 2010 renewed interest in the development of a universal vaccine toward PEDV. This report details several design changes made to a Hepatitis B virus core antigen (HBcAg)-based recombinant vaccine strategy, and their effect in vivo. Initially, several multi-antigen vaccine candidates were able to elicit antibodies specific to three out of four B-cell epitopes inserted into the chimeric proteins. However, a lack of virus neutralization led to a redesign of the vaccines. The focus of the newly redesigned vaccines was to elicit a strong immune response to the YSNIGVCK amino acid motif from PEDV. Genetically modified new vaccine candidates were able to elicit a strong antibody (Ab) response to the YSNIGVCK epitope, which correlated with an increased ability to neutralize the CO strain of PEDV. Additionally, the location of the inserted PEDV epitopes within the vector protein was shown to affect the immune recognition toward the native HBcAg during vaccination.

A Simple Add-and-Display Method for Immobilisation of Cancer Drug on His-tagged Virus-like Nanoparticles for Controlled Drug Delivery

pH-responsive virus-like nanoparticles (VLNPs) hold promising potential as drug delivery systems for cancer therapy. In the present study, hepatitis B virus (HBV) VLNPs harbouring His-tags were used to display doxorubicin (DOX) via nitrilotriacetic acid (NTA) conjugation. The His-tags served as pH-responsive nanojoints which released DOX from VLNPs in a controlled manner. The His-tagged VLNPs conjugated non-covalently with NTA-DOX, and cross-linked with folic acid (FA) were able to specifically target and deliver the DOX into ovarian cancer cells via folate receptor (FR)-mediated endocytosis. The cytotoxicity and cellular uptake results revealed that the His-tagged VLNPs significantly increased the accumulation of DOX in the ovarian cancer cells and enhanced the uptake of DOX, which improved anti-tumour effects. This study demonstrated that NTA-DOX can be easily displayed on His-tagged VLNPs by a simple Add-and-Display step with high coupling efficiency and the drug was only released at low pH in a controlled manner. This approach facilitates specific attachment of any drug molecule on His-tagged VLNPs at the very mild conditions without changing the biological structure and native conformation of the VLNPs.