Synthesis and Immunological Study of N-Glycan-Bacteriophage Qß Conjugates Reveal Dominant Antibody Responses to the Conserved Chitobiose Core.

N-Glycosylation plays an important role in many biological recognition processes. However, very few N-glycan-specific antibodies are available for functional studies and potentially for therapeutic development. In this study, we sought to synthesize bacteriophage Qß conjugates with representative N-glycans and investigate their immunogenicity for raising N-glycan-specific antibodies. An array of Qß glycoconjugates bearing five different human N-glycans and two different chemical linkers were synthesized, and the immunization of the N-glycan-Qß conjugates was performed in mice. We found that the N-glycan-Qß conjugates raised significant IgG antibodies that recognize N-glycans, but, surprisingly, most of the glycan-dependent antibodies were directed to the shared chitobiose core and were nonspecific for respective N-glycan structures. The linker chemistry was found to affect antibody specificity with adipic acid-linked N-glycan-Qß immunogens raising antibodies capable of recognizing both the N-acetylglucosamine (GlcNAc) moieties of the chitobiose core. In contrast, antibodies raised by N-glycan-Qß immunogens with a triazole linker preferentially recognized the innermost N-acetylglucosamine moiety at the reducing end. We also found that sialylation of the N-glycans significantly suppressed the immune response. Furthermore, the N-glycan-Qß immunogens with an adipic acid linker elicited higher glycan-specific antibody titers than the N-glycan-triazole-Qß immunogens. These findings delineate several challenges in eliciting mammalian N-glycan-specific antibodies through the conventional glycoconjugate vaccine design and immunization.

Structure Guided Design of Bacteriophage Qß Mutants as Next Generation Carriers for Conjugate Vaccines.

Vaccines are critical tools to treat and prevent diseases. For an effective conjugate vaccine, the carrier is crucial, but few carriers are available for clinical applications. In addition, a drawback of current protein carriers is that high levels of antibodies against the carrier are induced by the conjugate vaccine, which are known to interfere with the immune responses against the target antigen. To overcome these challenges, we obtained the near atomic resolution crystal structure of an emerging protein carrier, i.e., the bacteriophage Qß virus like particle. On the basis of the detailed structural information, novel mutants of bacteriophage Qß (mQß) have been designed, which upon conjugation with tumor associated carbohydrate antigens (TACAs), a class of important tumor antigens, elicited powerful anti-TACA IgG responses and yet produced lower levels of anticarrier antibodies as compared to those from the wild type Qß-TACA conjugates. In a therapeutic model against an aggressive breast cancer in mice, 100% unimmunized mice succumbed to tumors in just 12 days even with chemotherapy. In contrast, 80% of mice immunized with the mQß-TACA conjugate were completely free from tumors. Besides TACAs, to aid in the development of vaccines to protect against COVID-19, the mQß based conjugate vaccine has been shown to induce high levels of IgG antibodies against peptide antigens from the SARS-CoV-2 virus, demonstrating its generality. Thus, mQß is a promising next-generation carrier platform for conjugate vaccines, and structure-based rational design is a powerful strategy to develop new vaccine carriers.

Chemoenzymatic Synthesis and Antibody Binding of HIV-1 V1/V2 Glycopeptide-Bacteriophage Qß Conjugates as a Vaccine Candidate.

The broadly neutralizing antibody PG9 recognizes a unique glycopeptide epitope in the V1V2 domain of HIV-1 gp120 envelope glycoprotein. The present study describes the design, synthesis, and antibody-binding analysis of HIV-1 V1V2 glycopeptide-Qß conjugates as a mimic of the proposed neutralizing epitope of PG9. The glycopeptides were synthesized using a highly efficient chemoenzymatic method. The alkyne-tagged glycopeptides were then conjugated to the recombinant bacteriophage (Qß), a virus-like nanoparticle, through a click reaction. Antibody-binding analysis indicated that the synthetic glycoconjugates showed significantly enhanced affinity for antibody PG9 compared with the monomeric glycopeptides. It was also shown that the affinity of the Qß-conjugates for antibody PG9 was dependent on the density of the glycopeptide antigen display. The glycopeptide-Qß conjugates synthesized represent a promising candidate of HIV-1 vaccine.

Single-Point Mutations in Qß Virus-like Particles Change Binding to Cells.

Virus-like particles (VLPs) constitute large, polyvalent platforms onto which a wide variety of functional units can be grafted. Their use in biological settings often depends on their specific binding to cells or receptors of interest; this can be compromised by excessive nonspecific association with other cells. We found that lysine residues mediate such nonspecific interactions, presumably by virtue of protonation and interaction with anionic membrane lipid headgroups and/or complementary residues of cell surface proteins and polysaccharides. Chemical acylation of surface-exposed amines of the Qß VLP led to a significant reduction in the association of particles with mammalian cells. Single-point mutations of particular lysine residues to either glutamine, glutamic acid, tryptophan, or phenylalanine were mostly well-tolerated and formed intact capsids, but the introduction of double and triple mutants was far less forgiving. Introduction of glutamic acid at position 13 (K13E) led to a dramatic increase in cellular binding, whereas removal of the lysine at position 46 (K46Q) led to an equally striking reduction. Several plasma membrane components were found to specifically interact with the Qß capsid irrespective of surface charge. These results suggest that specific cellular interactions are engaged or obviated by such mutations and provide us with more "benign" particles to which can be added binding functionality for targeted delivery applications.

Overcoming the design, build, test bottleneck for synthesis of nonrepetitive protein-RNA cassettes.

We apply an oligo-library and machine learning-approach to characterize the sequence and structural determinants of binding of the phage coat proteins (CPs) of bacteriophages MS2 (MCP), PP7 (PCP), and Qß (QCP) to RNA. Using the oligo library, we generate thousands of candidate binding sites for each CP, and screen for binding using a high-throughput dose-response Sort-seq assay (iSort-seq). We then apply a neural network to expand this space of binding sites, which allowed us to identify the critical structural and sequence features for binding of each CP. To verify our model and experimental findings, we design several non-repetitive binding site cassettes and validate their functionality in mammalian cells. We find that the binding of each CP to RNA is characterized by a unique space of sequence and structural determinants, thus providing a more complete description of CP-RNA interaction as compared with previous low-throughput findings. Finally, based on the binding spaces we demonstrate a computational tool for the successful design and rapid synthesis of functional non-repetitive binding-site cassettes.

The developing toolkit of continuous directed evolution.

Continuous directed evolution methods allow the key steps of evolution-gene diversification, selection, and replication-to proceed in the laboratory with minimal researcher intervention. As a result, continuous evolution can find solutions much more quickly than traditional discrete evolution methods. Continuous evolution also enables the exploration of longer and more numerous evolutionary trajectories, increasing the likelihood of accessing solutions that require many steps through sequence space and greatly facilitating the iterative refinement of selection conditions and targeted mutagenesis strategies. Here we review the historical advances that have expanded continuous evolution from its earliest days as an experimental curiosity to its present state as a powerful and surprisingly general strategy for generating tailor-made biomolecules, and discuss more recent improvements with an eye to the future.

Phage capsid nanoparticles with defined ligand arrangement block influenza virus entry.

Multivalent interactions at biological interfaces occur frequently in nature and mediate recognition and interactions in essential physiological processes such as cell-to-cell adhesion. Multivalency is also a key principle that allows tight binding between pathogens and host cells during the initial stages of infection. One promising approach to prevent infection is the design of synthetic or semisynthetic multivalent binders that interfere with pathogen adhesion1-4. Here, we present a multivalent binder that is based on a spatially defined arrangement of ligands for the viral spike protein haemagglutinin of the influenza A virus. Complementary experimental and theoretical approaches demonstrate that bacteriophage capsids, which carry host cell haemagglutinin ligands in an arrangement matching the geometry of binding sites of the spike protein, can bind to viruses in a defined multivalent mode. These capsids cover the entire virus envelope, thus preventing its binding to the host cell as visualized by cryo-electron tomography. As a consequence, virus infection can be inhibited in vitro, ex vivo and in vivo. Such highly functionalized capsids present an alternative to strategies that target virus entry by spike-inhibiting antibodies5 and peptides6 or that address late steps of the viral replication cycle7.

Bacteriophage Qß virus-like particles displaying Chikungunya virus B-cell epitopes elicit high-titer E2 protein antibodies but fail to neutralize a Thailand strain of Chikungunya virus.

Chikungunya virus (CHIKV) is a mosquito-borne virus associated with arthritis and musculoskeletal pains. More than 2.9 million people worldwide have been infected with the virus within the last 1.5 decades; currently, there are no approved vaccines to protect against CHIKV infection. To assess the potential of using CHIKV peptides as vaccine antigens, we multivalently displayed CHIKV peptides representing B-cell epitopes (amino acids 2800-2818, 3025-3058, 3073-3081, 3121-3146, and 3177-3210), from E2 glycoprotein (Singapore strain), on the surface of a highly immunogenic bacteriophage Qß virus-like particle (VLP). We assessed the immunogenicity of CHIKV E2 amino acid 3025-3058 (including the other epitopes) displayed on Qß VLPs in comparison to the same peptide not displayed on VLPs. Mice immunized with the E2 peptides displayed on Qß VLPs elicited high-titer antibodies compared with the group immunized just with the peptide. However, sera from immunized mice did not neutralize CHIKV AF15561 (isolated from Thailand). The data suggest that Qß VLPs is an excellent approach to elicit high-titer CHIKV E2-protein antibodies at a lower dose of antigen and future studies should assess whether Qß-CHIKV E2 aa 2800-2818 VLPs and Qß-CHIKV E2 aa 3025-3058 VLPs can neutralize a Singapore Strain of CHIKV.

Synthesis and Immunological Evaluation of Disaccharide Bearing MUC-1 Glycopeptide Conjugates with Virus-like Particles.

Mucin-1 (MUC1) is a highly attractive antigenic target for anticancer vaccines. Naturally existing MUC1 can contain multiple types of O-linked glycans, including the Thomsen-Friedenreich (Tf) antigen and the Sialyl Thomsen-nouveau (STn) antigen. In order to target these antigens as potential anticancer vaccines, MUC1 glycopeptides SAPDT*RPAP (T* is the glycosylation site) bearing the Tf and the STn antigen, respectively, have been synthesized. The bacteriophage Qß carrier is a powerful carrier for antigen delivery. The conjugates of MUC1-Tf and -STn glycopeptides with Qß were utilized to immunize immune-tolerant human MUC1 transgenic (MUC1.Tg) mice, which elicited superior levels of anti-MUC1 IgG antibodies with titers reaching over 2 million units. The IgG antibodies recognized a wide range of MUC1 glycopeptides bearing diverse glycans. Antibodies induced by Qß-MUC1-Tf showed strongest binding, with MUC1-expressing melanoma B16-MUC1 cells, and effectively killed these cells in vitro. Vaccination with Qß-MUC1-Tf first followed by tumor challenge in a lung metastasis model showed significant reductions of the number of tumor foci in the lungs of immunized mice as compared to those in control mice. This was the first time that a MUC1-Tf-based vaccine has shown in vivo efficacy in a tumor model. As such, Qß-MUC1 glycopeptide conjugates have great potential as anticancer vaccines.

Lung Tissue Delivery of Virus-Like Particles Mediated by Macrolide Antibiotics.

Macrophage cells are present in high abundance in the lung to intercept invading microorganisms that gain access through airway mucosal surfaces. Several bacterial pathogens have evolved the capacity to evade the innate immune response by establishing infections within pulmonary macrophages upon phagocytosis, leading to prolonged disease. Macrolide antibiotics such as azithromycin and clarithromycin accumulate in phagocytic cells and have been shown to preferentially distribute in tissues where populations of these cells reside. We employed this class of molecules as targeting ligands to direct virus-like particles (VLPs) to lung-resident macrophages. VLP-macrolide conjugates showed enhanced uptake into RAW 264.7 macrophage cells in culture, with azithromycin displaying the greatest effect; distinct differences were also observed for different macrocycle structures and orientations on the particle surface. Activation of macrophage cells was stimulated by particle uptake toward an intermediate activation state, in contrast to previous reports using macrolide-functionalized gold nanorods that stimulated a cytotoxic macrophage response. Attached azithromycin was also able to direct VLPs to the lungs in mice, with significant accumulation within 2 h of systemic injection. These results suggest that this new class of bioconjugate could serve as an effective platform for intracellular drug delivery in the context of pulmonary infections.

A Direct RNA-to-RNA Replication System for Enhanced Gene Expression in Bacteria.

A long-standing objective of metabolic engineering has been to exogenously increase the expression of target genes. In this research, we proposed the permanent RNA replication system using DNA as a template to store genetic information in bacteria. We selected Qß phage as the RNA replication prototype and made many improvements to achieve target gene expression enhancement directly by increasing mRNA abundance. First, we identified the endogenous gene Rnc, the knockout of which significantly improved the RNA replication efficiency. Second, we elucidated the essential elements for RNA replication and optimized the system to make it more easily applicable. Combined with optimization of the host cell and the system itself, we developed a stable RNA-to-RNA replication tool to directly increase the abundance of the target mRNA and subsequently the target protein. Furthermore, it was proven efficient in enhancing the expression of specific proteins and was demonstrated to be applicable in metabolic engineering. Our system has the potential to be combined with any of the existing methods for increasing gene expression.

Synthetic and immunological studies of Salmonella Enteritidis O-antigen tetrasaccharides as potential anti-Salmonella vaccines.

The first synthetic carbohydrate based potential anti-Salmonella Enteritidis vaccine has been developed by conjugating a synthetic tetrasaccharide antigen with bacteriophage Qß. High levels of specific and long lasting anti-glycan IgG antibodies were induced by the conjugate, which completely protected mice from lethal bacterial challenges in a passive transfer model.

Protective Epitope Discovery and Design of MUC1-based Vaccine for Effective Tumor Protections in Immunotolerant Mice.

Human mucin-1 (MUC1) is a highly attractive antigen for the development of anticancer vaccines. However, in human clinical trials of multiple MUC1 based vaccines, despite the generation of anti-MUC1 antibodies, the antibodies often failed to exhibit much binding to tumor presumably due to the challenges in inducing protective immune responses in the immunotolerant environment. To design effective MUC1 based vaccines functioning in immunotolerant hosts, vaccine constructs were first synthesized by covalently linking the powerful bacteriophage Qß carrier with MUC1 glycopeptides containing 20-22 amino acid residues covering one full length of the tandem repeat region of MUC1. However, IgG antibodies elicited by these first generation constructs in tolerant human MUC1 transgenic (Tg) mice did not bind tumor cells strongly. To overcome this, a peptide array has been synthesized. By profiling binding selectivities of antibodies, the long MUC1 glycopeptide was found to contain immunodominant but nonprotective epitopes. Critical insights were obtained into the identity of the key protective epitope. Redesign of the vaccine focusing on the protective epitope led to a new Qß-MUC1 construct, which was capable of inducing higher levels of anti-MUC1 IgG antibodies in MUC1.Tg mice to react strongly with and kill a wide range of tumor cells compared to the construct containing the gold standard protein carrier, i.e., keyhole limpet hemocyanin. Vaccination with this new Qß-MUC1 conjugate led to significant protection of MUC1.Tg mice in both metastatic and solid tumor models. The antibodies exhibited remarkable selectivities toward human breast cancer tissues, suggesting its high translational potential.

RNA chaperone assisted intramolecular annealing reaction towards oligouridylated RNA detection in cancer cells.

Proximity induced intramolecular nucleotide strand displacement, which can be simply performed in a single tube or in a complex cellular environment, is one of the key mechanisms for the detection of biological targets, especially for significant genetic molecules. The host factor for RNA phage Qb replication (Hfq), with two distinct single stranded RNA binding sites, has excellent properties as an affinity ligand in a proximity induced reaction. In this research, a versatile RNA chaperone-Hfq assisted RNA annealing strategy for the sensitive detection of the intermediate product, oligouridylated RNA, in a genetic regulation process was developed. Benefiting from the high binding affinity of Hfq for the probe and the target, the sensitive determination of oligouridylated RNA in cell lysis and human cervical cancer (HeLa) cells was successfully achieved. This study has also revealed that the Hfq assisted RNA annealing strategy can be further extended and applied in specific microRNA analysis, and RNA related tumorigenicity and disease diagnosis.

Site-Selective Nucleation and Size Control of Gold Nanoparticle Photothermal Antennae on the Pore Structures of a Virus.

In this Article, we show that the surface of the bacteriophage Qß is equipped with natural ligands for the synthesis of small gold nanoparticles (AuNPs). By exploiting disulfides in the protein secondary structure and the geometry formed from the capsid quaternary structure, we find that we can produce regularly arrayed patterns of ∼6 nm AuNPs across the surface of the virus-like particle. Experimental and computational analyses provide insight into the formation and stability of this composite. We further show that the entrapped genetic material can hold upward of 500 molecules of the anticancer drug Doxorubicin without leaking and without interfering with the synthesis of the AuNPs. This direct nucleation of nanoparticles on the capsid allows for exceptional conduction of photothermal energy upon nanosecond laser irradiation. As a proof of principle, we demonstrate that this energy is capable of rapidly releasing the drug from the capsid without heating the bulk solution, allowing for highly targeted cell killing in vitro.

Photodynamic inactivation of non-enveloped RNA viruses.

We recently reported the photodynamic inactivation (PDI) of bacteriophage MS2 with a photosensitiser- 5, 10, 15, 20-tetrakis (1-methyl-4-pyridinio) porphyrin- tetra- p-toluene sulfonate (TMPyP) in solution and concluded that the A-protein of the virus is the main target of inactivation. Here, we have extended these studies and carried out PDI of bacteriophage Qß, bovine enterovirus 2 (BEV-2) and type 1 murine norovirus (MNV-1). The rate of inactivation observed was in the order MS2 > Qß > MNV-1 > BEV-2. Data suggested that TMPyP-treatment could also target the viral genome as well as result in disintegration/disassembly of viral particles. Although emergence of viral drug resistance is a well-documented phenomenon, it was not possible to generate PDI-resistant MS2. However, emergence of a mutation in the lysis protein was detected after serial exposure to PDI.

Polyvalent Hybrid Virus-Like Nanoparticles with Displayed Heparin Antagonist Peptides.

The potential applications for nanomaterials continue to grow as new materials are developed and environmental and safety concerns are more adequately addressed. In particular, virus-like particles (VLPs) have myriad applications in medicine and biology, exploiting both the reliable, symmetric self-assembly mechanism and the ability to take advantage of surface functionalities that may be appropriately modified through mutation or bioconjugation. Herein we describe the design and application of hybrid VLPs for use as potent heparin antagonists, providing an alternative to the toxic heparin antidote protamine. A two-plasmid system was utilized to generate VLPs that contain both the wild-type coat protein and a second coat protein with either a C- or N-terminal cationic peptide extension (4-28 amino acids). Incorporation of the modified coat proteins varied from 8 to 31%, while activated partial thromboplastin time (APTT) assays revealed a range of the heparin antagonist activity. Notably, when examined on the basis of the quantity of peptide delivered due to the varied incorporation rates, it appeared that the VLPs largely followed a similar trend, with the quantity of peptide delivered more closely correlating with heparin antagonist activity. The particle with the highest incorporation rate and best antiheparin activity displayed the C-terminal peptide ARK2A2KA, which corresponds to the Cardin-Weintraub consensus sequence for binding to glycosaminoglycans. Analysis of this particle using heparin affinity chromatography with fraction collection revealed that particles eluting at higher salt concentration had a greater proportion of peptide incorporation. Preliminary dual polarization interferometry experiments further support a strong interaction between this particle and heparin.

Regulating the Uptake of Viral Nanoparticles in Macrophage and Cancer Cells via a pH Switch.

Controlling the uptake of nanomaterials into phagocytes is a challenging problem. We describe an approach to inhibit the cellular uptake by macrophages and HeLa cells of nanoparticles derived from bacteriophage Qß by conjugating negatively charged terminal hexanoic acid moieties onto its surface. Additionally, we show hydrazone linkers can be installed between the surface of Qß and the terminal hexanoic acid moieties, resulting in a pH-responsive conjugate that, in acidic conditions, can release the terminal hexanoic acid moiety and allow for the uptake of the Qß nanoparticle. The installation of the "pH switch" did not change the structure-function properties of the hexanoic acid moiety and the uptake of the Qß conjugates by macrophages.

The quest for quasispecies.

This month marks 40 years since the publication of 'Nucleotide sequence heterogeneity of an RNA phage population' in Cell. We spoke with Esteban Domingo, leading author of this landmark study carried out during his postdoctoral work in Charles Weissman's lab, which proposed RNA viral populations to be quasispecies.

B Cell-Intrinsic MyD88 Signaling Promotes Initial Cell Proliferation and Differentiation To Enhance the Germinal Center Response to a Virus-like Particle.

Although TLR signaling in B cells has been implicated in the germinal center (GC) responses during viral infections and autoimmune diseases, the underlying mechanism is unclear. Bacterial phage Qß-derived virus-like particle (Qß-VLP) contains TLR ligands, which can enhance Qß-VLP-induced Ab response, including GC response, through TLR/MyD88 signaling in B cells. In this study, by examining Ag-specific B cell response to Qß-VLP, we found that lack of B cell MyD88 from the beginning of the immune response led to a more severe defect in the GC scale than abolishing MyD88 at later time points of the immune response. Consistently, B cell-intrinsic MyD88 signaling significantly enhanced the initial proliferation of Ag-specific B cells, which was accompanied with a dramatic increase of plasma cell generation and induction of Bcl-6+ GC B cell precursors. In addition, B cell-intrinsic MyD88 signaling promoted strong T-bet expression independent of IFN-γ and led to the preferential isotype switching to IgG2a/c. Thus, by promoting the initial Ag-specific B cell proliferation and differentiation, B cell-intrinsic MyD88 signaling enhanced both T-independent and T-dependent Ab responses elicited by Qß-VLP. This finding will provide additional insight into the role of TLR signaling in antiviral immunity, autoimmune diseases, and vaccine design.