A vulnerable, membrane-proximal site in human respiratory syncytial virus F revealed by a prefusion-specific single-domain antibody

Small but Mighty: Nanobodies in the Fight Against Infectious Diseases

Infectious diseases, caused by pathogenic microorganisms and capable of spreading, pose a significant threat to global public health. Developing efficient and cost-effective techniques for treating infectious diseases is crucial in curbing their progression and reducing patients' morbidity and mortality. Nanobodies (Nbs), a novel class of affinity reagents derived from unique heavy chain-only antibodies in camelids, represent the smallest intact and fully functional antigen-binding fragments. Compared with conventional antibodies and their antigen binding fragments, Nbs offer numerous advantages, including high affinity, exceptional target specificity, cost-effective production, easy accessibility, and robust stability, demonstrating immense potential in infectious disease treatment. This review introduces Nbs and focuses on discussing their mechanisms and intervention strategies in the treatment of viral and bacterial infections.

DS2 designer pre-fusion F vaccine induces strong and protective antibody response against RSV infection

DS-Cav1, SC-TM, and DS2 are distinct designer pre-fusion F proteins (pre-F) of respiratory syncytial virus (RSV) developed for vaccines. However, their immunogenicity has not been directly compared. In this study, we generated three recombinant vaccines using the chimpanzee adenovirus vector AdC68 to express DS-Cav1, SC-TM, and DS2. All three vaccines elicited robust serum binding and neutralizing antibodies following intramuscular priming and boosting. DS2 induced the strongest antibody responses, followed by SC-TM and DS-Cav1. DS2 also provided strong protection against live RSV challenge. Monoclonal antibodies (mAbs) isolated from long-lived antibody-secreting cells (ASCs) in the bone marrow six months post-immunization with AdC68-DS2 predominantly targeted site Ø as well as site II. One neutralizing antibody against site II, mAb60, conferred strong protection against live RSV infection in mice. These findings highlight the strong ability of the DS2 design in eliciting long-lived antibody responses and guide the development of next-generation RSV vaccines.

Design, synthesis and antiviral evaluation of triazole-linked 7-hydroxycoumarin-monoterpene conjugates as inhibitors of RSV replication

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infections in babies across the world. Irrespective of progress in the development of RSV vaccines, effective small molecule drugs are still not available on the market. Based on our previous data we designed and synthesized triazole-linked coumarin-monoterpene hybrids and showed that they are indeed effective in inhibiting the RSV replication. The most effective compounds are active against both RSV serotypes, A and B, with IC50 in the low micromolar or submicromolar range of concentrations. These are the most active coumarin derivatives found so far. Compound 45 combining 3,7-dimethyloctane and cyclopentane-annealed coumarin fragments has a selectivity index of 160 for serotype A and 1147 for serotype B. According to the results of the time-of-addition experiments, the conjugates are active at the early stages of the virus cycle. Based on biological evaluation and molecular modeling data, RSV F protein is a possible target.

Direct and Ultrasensitive Bioluminescent Detection of Intact Respiratory Viruses

Respiratory viruses such as SARS-CoV-2, influenza, and respiratory syncytial virus (RSV) represent pressing health risks. Rapid diagnostic tests for these viruses detect single antigens or nucleic acids, which do not necessarily correlate with the amount of the intact virus. Instead, specific detection of intact respiratory virus particles may be more effective at assessing the contagiousness of a patient. Here, we report GLOVID, a modular biosensor platform to detect intact virions against a background of "free" viral proteins in solution. Our approach harnesses the multivalent display of distinct proteins on the surface of a viral particle to template the reconstitution of a split luciferase, allowing specific, single-step detection of intact influenza A and RSV virions corresponding to 0.1-0.3 fM of genomic units. The protein ligation system used to assemble GLOVID sensors is compatible with a broad range of binding domains, including nanobodies, scFv fragments, and cyclic peptides, which allows straightforward adjustment of the sensor platform to target different viruses.

Integrated cryoEM structure of a spumaretrovirus reveals cross-kingdom evolutionary relationships and the molecular basis for assembly and virus entry

Foamy viruses (FVs) are an ancient lineage of retroviruses, with an evolutionary history spanning over 450 million years. Vector systems based on Prototype Foamy Virus (PFV) are promising candidates for gene and oncolytic therapies. Structural studies of PFV contribute to the understanding of the mechanisms of FV replication, cell entry and infection, and retroviral evolution. Here we combine cryoEM and cryoET to determine high-resolution in situ structures of the PFV icosahedral capsid (CA) and envelope glycoprotein (Env), including its type III transmembrane anchor and membrane-proximal external region (MPER), and show how they are organized in an integrated structure of assembled PFV particles. The atomic models reveal an ancient retroviral capsid architecture and an unexpected relationship between Env and other class 1 fusion proteins of the Mononegavirales. Our results represent the de novo structure determination of an assembled retrovirus particle.

Bioluminescent detection of viral surface proteins using branched multivalent protein switches

Fast and reliable virus diagnostics is key to prevent the spread of viruses in populations. A hallmark of viruses is the presence of multivalent surface proteins, a property that can be harnessed to control conformational switching in sensor proteins. Here, we introduce a new sensor platform (dark-LUX) for the detection of viral surface proteins consisting of a general bioluminescent framework that can be post-translationally functionalized with separately expressed binding domains. The platform relies on (1) plug-and-play bioconjugation of different binding proteins via SpyTag/SpyCatcher technology to create branched protein structures, (2) an optimized turn-on bioluminescent switch based on complementation of the split-luciferase NanoBiT upon target binding and (3) straightforward exploration of the protein linker space. The influenza A virus (IAV) surface proteins hemagglutinin (HA) and neuraminidase (NA) were used as relevant multivalent targets to establish proof of principle and optimize relevant parameters such as linker properties, choice of target binding domains and the optimal combination of the competing NanoBiT components SmBiT and DarkBiT. The sensor framework allows rapid conjugation and exchange of various binding domains including scFvs, nanobodies and de novo designed binders for a variety of targets, including the construction of a heterobivalent switch that targets the head and stem region of hemagglutinin. The modularity of the platform thus allows straightforward optimization of binding domains and scaffold properties for existing viral targets, and is well suited to quickly adapt bioluminescent sensor proteins to effectively detect newly evolving viral epitopes.

A neutralizing single-domain antibody that targets the trimer interface of the human metapneumovirus fusion protein

IMPORTANCE

Human metapneumovirus (hMPV) is an important respiratory pathogen for which no licensed antivirals or vaccines exist. Single-domain antibodies represent promising antiviral biologics that can be easily produced and formatted. We describe the isolation and detailed characterization of two hMPV-neutralizing single-domain antibodies that are directed against the fusion protein F. One of these single-domain antibodies broadly neutralizes hMPV A and B strains, can prevent proteolytic maturation of F, and binds to an epitope in the F trimer interface. This suggests that hMPV pre-F undergoes trimer opening or "breathing" on infectious virions, exposing a vulnerable site for neutralizing antibodies. Finally, we show that this single-domain antibody, fused to a human IgG1 Fc, can protect cotton rats against hMPV replication, an important finding for potential future clinical applications.

New Inhibitors of Respiratory Syncytial Virus (RSV) Replication Based on Monoterpene-Substituted Arylcoumarins

Respiratory syncytial virus (RSV) causes annual epidemics of respiratory infection. Usually harmless to adults, the RSV infection can be dangerous to children under 3 years of age and elderly people over 65 years of age, often causing serious problems, even death. At present, there are no vaccines and specific chemotherapeutic agents for the treatment of this disease, so the search for low-molecular weight compounds to combat RSV is a challenge. In this work, we have shown, for the first time, that monoterpene-substituted arylcoumarins are efficient RSV replication inhibitors at low micromolar concentrations. The most active compound has a selectivity index of about 200 and acts most effectively at the early stages of infection. The F protein of RSV is a potential target for these compounds, which is also confirmed by molecular docking and molecular dynamics simulation data.

Single-Domain Antibodies as Therapeutics for Respiratory RNA Virus Infections

Over the years, infectious diseases with high morbidity and mortality disrupted human healthcare systems and devastated economies globally. Respiratory viruses, especially emerging or re-emerging RNA viruses, including influenza and human coronavirus, are the main pathogens of acute respiratory diseases that cause epidemics or even global pandemics. Importantly, due to the rapid mutation of viruses, there are few effective drugs and vaccines for the treatment and prevention of these RNA virus infections. Of note, a class of antibodies derived from camelid and shark, named nanobody or single-domain antibody (sdAb), was characterized by smaller size, lower production costs, more accessible binding epitopes, and inhalable properties, which have advantages in the treatment of respiratory diseases compared to conventional antibodies. Currently, a number of sdAbs have been developed against various respiratory RNA viruses and demonstrated potent therapeutic efficacy in mouse models. Here, we review the current status of the development of antiviral sdAb and discuss their potential as therapeutics for respiratory RNA viral diseases.

Monoterpene-Containing Substituted Coumarins as Inhibitors of Respiratory Syncytial Virus (RSV) Replication

Respiratory syncytial virus (RSV) is a critical cause of infant mortality. However, there are no vaccines and adequate drugs for its treatment. We showed, for the first time, that O-linked coumarin-monoterpene conjugates are effective RSV inhibitors. The most potent compounds are active against both RSV serotypes, A and B. According to the results of the time-of-addition experiment, the conjugates act at the early stages of virus cycle. Based on molecular modelling data, RSV F protein may be considered as a possible target.