Disordered epitopes as peptide vaccines

Iodine-mediated decarboxylative coupling to synthesize β-sulfonyl-ene-amines/2,3-diarythio-pyrroles from α-amino acids and sodium sulfinates

A novel process has been developed for the selective synthesis of β-sulfonyl-enamines and 2,3-diarylthiopyrroles. This process utilizes the decarboxylative coupling and β-C(sp3)-H functionalization of α-amino acids. In this reaction, iodine functions dually as a tandem catalyst to initiate the decarboxylation of α-amino acids and as an oxidant to facilitate the formation of organic sulfides. This innovative approach not only simplifies the synthesis but also enhances the yield and selectivity of the desired products.

Revisiting Protein-Copolymer Binding Mechanisms: Insights beyond the "Lock-and-Key" Model

The "lock-and-key" model that emphasizes the concept of chemical-structural complementary is the key mechanism for explaining the selectivity between small ligands and a larger adsorbent molecule. In this work, concerning the copolymer chain using only the combination of N-isopropylacrylamide (NIPAm) and hydrophobic N-tert-butylacrylamide (TBAm) monomers and by large-scale atomistic molecular dynamics simulations, our results show that the flexible copolymer chain may exhibit strong binding affinity for the biomarker protein epithelial cell adhesion molecule, in the absence of hydrophobic matching and strong structural complementarity. This surprising binding behavior, which cannot be anticipated by the "lock-and-key" model, can be attributed to the preferential interactions established by the copolymer with the protein's hydrophilic exterior. We observe that increasing the fraction of incorporated TBAm monomers leads to a prevalence of interactions with asparagine and glutamine amino acids due to the emerging hydrogen bonding with both NIPAm and TBAm monomers. Our findings suggest the appearance of highly specific and high-affinity binding sites on the protein created by engineering the copolymer composition, which motivates the applications of copolymers as protein affinity reagents.

In silico analysis of sporozoite surface antigen 1 of Theileria annulata (TaSPAG1) for multi-epitope vaccine design against theileriosis

Tropical theileriosis is a protozoan infection caused by Theileria annulata, which significantly affects cattle worldwide. This study was aimed to analyze the TaSPAG1 protein and design a novel multi-epitope vaccine candidate. Online tools were employed for the prediction of Physico-chemical properties, antigenicity, allergenicity, solubility, transmembrane domains and signal peptide, posttranslational modification (PTM) sites, secondary and tertiary structures as well as intrinsically disordered regions, followed by identification and screening of potential linear and conformational B-cell epitopes and those peptides having affinity to bind bovine major histocompatibility complex class I (MHC-I) molecules. Next, a multi-epitope vaccine construct was designed and analyzed. This 907-residue protein was hydrophilic (GRAVY: -0.399) and acidic (pI: 5.04) in nature, with high thermotolerance (aliphatic: 71.27). Also, 5 linear and 12 conformational B-cell epitopes along with 8 CTL epitopes were predicted for TaSPAG1. The 355-residue vaccine candidate had a MW of about 35 kDa and it was antigenic, non-allergenic, soluble and stable, which was successfully interacted with cattle MHC-I molecule and finally cloned into the pET28a(+) vector. Further wet studies are required to assess the vaccine efficacy in cattle.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-023-00153-5.

In Silico Characterization of an Important Metacyclogenesis Marker in Leishmania donovani, HASPB1, as a Potential Vaccine Candidate

Visceral leishmaniasis is a life-threatening infectious disease worldwide. Extensive experiments have been done to introduce potential vaccine candidates to combat leishmaniasis. The present study was done to evaluate Leishmania donovani hydrophilic acylated surface protein B1 as a potential vaccine candidate using in silico methods. For this aim, server-based predictions were performed regarding physicochemical characteristics, solubility, antigenicity, allergenicity, signal peptide, transmembrane domain, and posttranslational modifications (PTMs). Also, secondary and tertiary structures were predicted using NetSurfP-3.0 and I-TASSER, respectively. The 3D model was further subjected to refinement and validation, and promising B-cell, cytotoxic T-lymphocyte (CTL; human, dog), and helper T-lymphocyte (HTL; human) epitopes were predicted. The protein had a molecular weight of 42.19 kDa, with high solubility (0.749), stability (instability index: 21.34), and hydrophilicity (GRAVY: -2.322). No signal peptide or transmembrane domain was predicted, and the most abundant PTMs were phosphorylation, O-glycosylation, and acetylation. Many coils and disordered regions existed in the secondary structure analysis, and the tertiary model had a good confidence score (-0.79). Next, the ProSA-web and PROCHECK tools showed adequate improvements in the refined model compared to the crude model. Only 4 shared B-cell epitopes among three web servers (ABCpred, BepiPred 2.0, and SVMTriP) were shown to be antigenic, nonallergenic, and with good water solubility. Also, five potent CTL epitopes in dogs and five in humans were predicted. Notably, two HTL epitopes were found to be potential IFN-γ inducers. In conclusion, our results demonstrated several immunogenic epitopes in this protein, which could be directed towards multiepitope vaccine design.

Molecular and functional properties of human Plasmodium falciparum CSP C-terminus antibodies

Human monoclonal antibodies (mAbs) against the central repeat and junction domain of Plasmodium falciparum circumsporozoite protein (PfCSP) have been studied extensively to guide malaria vaccine design compared to antibodies against the PfCSP C terminus. Here, we describe the molecular characteristics and protective potential of 73 germline and mutated human mAbs against the highly immunogenic PfCSP C-terminal domain. Two mAbs recognized linear epitopes in the C-terminal linker with sequence similarity to repeat and junction motifs, whereas all others targeted conformational epitopes in the α-thrombospondin repeat (α-TSR) domain. Specificity for the polymorphic Th2R/Th3R but not the conserved RII+/CS.T3 region in the α-TSR was associated with IGHV3-21/IGVL3-21 or IGLV3-1 gene usage. Although the C terminus specific mAbs showed signs of more efficient affinity maturation and class-switching compared to anti-repeat mAbs, live sporozoite binding and inhibitory activity was limited to a single C-linker reactive mAb with cross-reactivity to the central repeat and junction. The data provide novel insights in the human anti-C-linker and anti-α-TSR antibody response that support exclusion of the PfCSP C terminus from malaria vaccine designs.

Tuning the Cellular Uptake and Retention of Rhodamine Dyes by Molecular Engineering for High-Contrast Imaging of Cancer Cells

Probes allowing high-contrast discrimination of cancer cells and effective retention are powerful tools for the early diagnosis and treatment of cancer. However, conventional small-molecule probes often show limited performance in both aspects. Herein, we report an ingenious molecular engineering strategy for tuning the cellular uptake and retention of rhodamine dyes. Introduction of polar aminoethyl leads to the increased brightness and reduced cellular uptake of dyes, and this change can be reversed by amino acetylation. Moreover, these modifications allow cancer cells to take up more dyes than normal cells (16-fold) through active transport. Specifically, we further improve the signal contrast (56-fold) between cancer and normal cells by constructing activatable probes and confirm that the released fluorophore can remain in cancer cells with extended time, enabling long-term and specific tumor imaging.

In silico design of a TLR4-mediating multiepitope chimeric vaccine against amyotrophic lateral sclerosis via advanced immunoinformatics

Amyotrophic lateral sclerosis (ALS) is the most prevalent motor neuron disorder worldwide. In ALS, progressing disease can result from misfolding and aggregation of superoxide dismutase-1 (SOD1) or TAR DNA-binding protein 43 kDa (TDP43). An efficient immunotherapy for ALS should spare intact SOD1 while eliminating its dysfunctional variant. We utilized advanced immunoinformatics to suggest a potential vaccine candidate against ALS by proposing a model of dynamic TLR4 mediation and induction of a specific Th2-biased shift against mutant SOD1, TDP43, and TRAF6, a protein that specifically interacts with dysfunctional SOD1. SOD1, TDP43, and TRAF6 were retrieved in FASTA. Immune Epitopes Database and CTLpred suggested T/B-cell epitopes from disease-specific regions of selected antigens. A TLR4-mediating adjuvant, RS01, was used. Sequences were assembled via suitable linkers. Tertiary structure of the protein was calculated. Refined protein structure and physicochemical features of the 3D structure were verified in silico. Differential immune induction was assessed via C-ImmSim. GROningen MAchine for Chemical Simulation was used to assess evolution of the docked vaccine-TLR4 complex in blood. Our protein showed high structural quality and was nonallergenic and immune inducing. Also, the vaccine-TLR4 complex stability was verified by RMSD, RMSF, gyration, and visual analyses of the molecular dynamic trajectory. Contact residues in the vaccine-TLR4 complex showed favorable binding energies. Immune stimulation analyses of the proposed candidate demonstrated a sustained memory cell response and a strong adaptive immune reaction. We proposed a potential vaccine candidate against ALS and verified its physicochemical and immune inducing features. Future studies should assess this vaccine in animal studies.

Restriction of the Global IgM Repertoire in Antiphospholipid Syndrome

The typical anti-phospholipid antibodies (APLA) in the anti-phospholipid syndrome (APS) are reactive with the phospholipid-binding protein β2GPI as well as a growing list of other protein targets. The relation of APLA to natural antibodies and the fuzzy set of autoantigens involved provoked us to study the changes in the IgM repertoire in APS. To this end, peptides selected by serum IgM from a 7-residue linear peptide phage display library (PDL) were deep sequenced. The analysis was aided by a novel formal representation of the Igome (the mimotope set reflecting the IgM specificities) in the form of a sequence graph. The study involved women with APLA and habitual abortions (n=24) compared to age-matched clinically healthy pregnant women (n=20). Their pooled Igomes (297 028 mimotope sequences) were compared also to the global public repertoire Igome of pooled donor plasma IgM (n=2 796 484) and a set of 7-mer sequences found in the J regions of human immunoglobulins (n=4 433 252). The pooled Igome was represented as a graph connecting the sequences as similar as the mimotopes of the same monoclonal antibody. The criterion was based on previously published data. In the resulting graph, identifiable clusters of vertices were considered related to the footprints of overlapping antibody cross-reactivities. A subgraph based on the clusters with a significant differential expression of APS patients' mimotopes contained predominantly specificities underrepresented in APS. The differentially expressed IgM footprints showed also an increased cross-reactivity with immunoglobulin J regions. The specificities underexpressed in APS had a higher correlation with public specificities than those overexpressed. The APS associated specificities were strongly related also to the human peptidome with 1 072 mimotope sequences found in 7 519 human proteins. These regions were characterized by low complexity. Thus, the IgM repertoire of the APS patients was found to be characterized by a significant reduction of certain public specificities found in the healthy controls with targets representing low complexity linear self-epitopes homologous to human antibody J regions.

Determination of B and T Cell Epitopes in Neospora caninum Immune Mapped Protein-1 (IMP-1): Implications in Vaccine Design against Neosporosis

Prevention of neosporosis is advantageous for cattle health and productivity. Previously, several vaccine candidates were nominated for vaccination against Neospora caninum. This study was premised on in silico evaluation of N. caninum IMP-1 in order to determine its physicochemical features and immunogenic epitopes. We employed a wide array of network-based tools for the prediction of antigenicity, allergenicity, solubility, posttranslational modification (PTM) sites, physicochemical properties, transmembrane domains and signal peptide, secondary and tertiary structures, and intrinsically disordered regions. Also, prediction and screening of potential continuous B cell peptides and those epitopes having stringent affinity to couple with mouse major histocompatibility complex (MHC) and cytotoxic T lymphocyte (CTL) receptors were accomplished. The protein had 393 residues with a molecular weight of 42.71 kDa, representing aliphatic index of 85.83 (thermotolerant) and GRAVY score of -0.447 (hydrophilic). There were 47 PTM sites without a signal peptide in the sequence. Secondary structure comprised mostly of extended strand and helices, followed by coils. The Ramachandran plot of the refined model showed 90.1%, 9.9%, 0.0%, and 0.0% residues in the favored, additional allowed, generously allowed, and disallowed regions, correspondingly. Additionally, various potential B cell (linear and conformational), CTL, and MHC binding epitopes were predicted for N. caninum IMP-1. The findings of the present study could be further directed for next-generation vaccine design against neosporosis.

Neospora caninum SRS2 Protein: Essential Vaccination Targets and Biochemical Features for Next-Generation Vaccine Design

Vaccination is a standout preventive measure to combat neosporosis among cattle herds. The present in silico study was done to evaluate the physicochemical properties and potent immunogenic epitopes of N. caninum SRS2 protein as a possible vaccine candidate. Web-based tools were used to predict physicochemical properties, antigenicity, allergenicity, solubility, posttranslational modification (PTM) sites, transmembrane domains and signal peptide, and secondary and tertiary structures as well as intrinsically disordered regions, followed by identification and screening of potential linear and conformational B-cell epitopes and those peptides having affinity to bind mouse major histocompatibility complex (MHC) and cytotoxic T lymphocyte (CTL). The protein had 401 residues with a molecular weight of 42 kDa, representing aliphatic index of 69.35 (thermotolerant) and GRAVY score of -0.294 (hydrophilic). There were 53 PTM sites without a signal peptide in the sequence. Secondary structure comprised mostly by extended strand, followed by helices and coils. The Ramachandran plot of the refined model showed 90.2%, 8.8%, 0.5%, and 0.5% residues in the favored, additional allowed, generously allowed, and disallowed regions, correspondingly. Additionally, various potential B-cell (linear and conformational), CTL, and MHC-binding epitopes were predicted for N. caninum SRS2. These epitopes could be further utilized in the multiepitope vaccine constructs directed against neosporosis.

Linear Epitope Binding Patterns of Grass Pollen-Specific Antibodies in Allergy and in Response to Allergen-Specific Immunotherapy

Allergic diseases affect many individuals world-wide and are dependent on the interaction between allergens and antibodies of the IgE isotype. Allergen-specific immunotherapy (AIT) can alter the development of the disease, e.g., through induction of allergen-specific IgG that block allergen-IgE interactions. The knowledge of epitopes recognized by allergy-causing and protective antibodies are limited. Therefore, we developed an allergome-wide peptide microarray, aiming to track linear epitope binding patterns in allergic diseases and during AIT. Here, we focused on immune responses to grass pollen allergens and found that such epitopes were commonly recognized before initiation of AIT and that AIT commonly resulted in increased antibody production against additional epitopes already after 1 year of treatment. The linear epitope binding patterns were highly individual, both for subjects subjected to and for individuals not subjected to AIT. Still, antibodies against some linear epitopes were commonly developed during AIT. For example, the two rigid domains found in grass pollen group 5 allergens have previously been associated to a diversity of discontinuous epitopes. Here, we present evidence that also the flexible linker, connecting these domains, contains regions of linear epitopes against which antibodies are developed during AIT. We also describe some commonly recognized linear epitopes on Phl p 2 and suggest how antibodies against these epitopes may contribute to or prevent allergy in relation to a well-defined stereotyped/public IgE response against the same allergen. Finally, we identify epitopes that induce cross-reactive antibodies, but also antibodies that exclusively bind one of two highly similar variants of a linear epitope. Our findings highlight the complexity of antibody recognition of linear epitopes, with respect to both the studied individuals and the examined allergens. We expect that many of the findings in this study can be generalized also to discontinuous epitopes and that allergen peptide microarrays provide an important tool for enhancing the understanding of allergen-specific antibodies in allergic disease and during AIT.

Guiding the Immune Response to a Conserved Epitope in MSP2, an Intrinsically Disordered Malaria Vaccine Candidate

The malaria vaccine candidate merozoite surface protein 2 (MSP2) has shown promise in clinical trials and is in part responsible for a reduction in parasite densities. However, strain-specific reductions in parasitaemia suggested that polymorphic regions of MSP2 are immuno-dominant. One strategy to bypass the hurdle of strain-specificity is to bias the immune response towards the conserved regions. Two mouse monoclonal antibodies, 4D11 and 9H4, recognise the conserved C-terminal region of MSP2. Although they bind overlapping epitopes, 4D11 reacts more strongly with native MSP2, suggesting that its epitope is more accessible on the parasite surface. In this study, a structure-based vaccine design approach was applied to the intrinsically disordered antigen, MSP2, using a crystal structure of 4D11 Fv in complex with its minimal binding epitope. Molecular dynamics simulations and surface plasmon resonance informed the design of a series of constrained peptides that mimicked the 4D11-bound epitope structure. These peptides were conjugated to keyhole limpet hemocyanin and used to immunise mice, with high to moderate antibody titres being generated in all groups. The specificities of antibody responses revealed that a single point mutation can focus the antibody response towards a more favourable epitope. This structure-based approach to peptide vaccine design may be useful not only for MSP2-based malaria vaccines, but also for other intrinsically disordered antigens.

Improvement on Permeability of Cyclic Peptide/Peptidomimetic: Backbone N-Methylation as A Useful Tool

Peptides have a three-dimensional configuration that can adopt particular conformations for binding to proteins, which are well suited to interact with larger contact surface areas on target proteins. However, low cell permeability is a major challenge in the development of peptide-related drugs. In recent years, backbone N-methylation has been a useful tool for manipulating the permeability of cyclic peptides/peptidomimetics. Backbone N-methylation permits the adjustment of molecule’s conformational space. Several pathways are involved in the drug absorption pathway; the relative importance of each N-methylation to total permeation is likely to differ with intrinsic properties of cyclic peptide/peptidomimetic. Recent studies on the permeability of cyclic peptides/peptidomimetics using the backbone N-methylation strategy and synthetic methodologies will be presented in this review.

Short Disordered Epitope of CRTAM Ig-Like V Domain as a Potential Target for Blocking Antibodies

Class-I Restricted T Cell-Associated Molecule (CRTAM) is a protein that is expressed after T cell activation. The interaction of CRTAM with its ligand, nectin-like 2 (Necl2), is required for the efficient production of IL-17, IL-22, and IFNγ by murine CD4 T cells, and it plays a role in optimal CD8 T and NK cell cytotoxicity. CRTAM promotes the pro-inflammatory cytokine profile; therefore, it may take part in the immunopathology of autoimmune diseases such as diabetes type 1 or colitis. Thus, antibodies that block the interaction between CRTAM and Necl2 would be useful for controlling the production of these inflammatory cytokines. In this work, using bioinformatics predictions, we identified three short disordered epitopes (sDE1-3) that are located in the Ig-like domains of murine CRTAM and are conserved in mammalian species. We performed a structural analysis by molecular dynamics simulations of sDE1 (QHPALKSSKY, Ig-like V), sDE2 (QRNGEKSVVK, Ig-like C1), and sDE3 (CSTERSKKPPPQI, Ig-like C1). sDE1, which is located within a loop of the contact interface of the heterotypic interaction with Nectl2, undergoes an order–disorder transition. On the contrary, even though sDE2 and sDE3 are flexible and also located within loops, they do not undergo order–disorder transitions. We evaluated the immunogenicity of sDE1 and sDE3 through the expression of these epitopes in chimeric L1 virus-like particles. We confirmed that sDE1 induces polyclonal antibodies that recognize the native folding of CRTAM expressed in activated murine CD4 T cells. In contrast, sDE3 induces polyclonal antibodies that recognize the recombinant protein hCRTAM-Fc, but not the native CRTAM. Thus, in this study, an exposed disordered epitope in the Ig-like V domain of CRTAM was identified as a potential site for therapeutic antibodies.

B cell epitopes in the intrinsically disordered regions of neuraminidase and hemagglutinin proteins of H5N1 and H9N2 avian influenza viruses for peptide-based vaccine development

Avian influenza viruses (AIV) are very active in several parts of the globe and are the cause of huge economic loss for the poultry industry and also human fatalities. Three dimensional modeling was carried out for neuraminidase (NA) and hemagglutinin (HA) proteins of AIV. The C-score, estimated TM-Score, and estimated root-mean-square deviation (RMSD) score for NA of H5N1 were -1.18, 0.57 ± 0.15, and 9.8 ± 7.6, respectively. The C-score, estimated TM-Score, and estimated RMSD score for NA of H9N2 were -1.43, 0.54 ± 0.15, and 10.5 ± 4.6, respectively. The C-score, estimated TM-Score, and estimated RMSD score for HA of H5N1 were -0.03, 0.71 ± 0.12, and 7.7 ± 4.3, respectively. The C-score, estimated TM-Score, and estimated RMSD score for HA of H9N2 were -0.57, 0.64 ± 0.13, and 8.9 ± 4.6, respectively. Intrinsically disordered regions were identified for the NA and HA proteins of H5N1 and H9N2 with the use of PONDR program. Linear B cell epitope was predicted using BepiPred 2 program for NA and HA of H5N1 and H9N2 avian influenza strains. Discontinuous epitopes were predicted by Discotope 2 program. The linear epitopes that were considered likely to be immunogenic and within the intrinsically disordered region for the NA of H5N1 was TKSTNSRSGFEMIWDPNGWTGTDSSFSVK, and for H9N2 it was VGDTPRNDDSSSSSNCRDPNNERGAP. In the case of HA of H5N1, it was QRLVPKIATRSKVNGQSG and ATGLRNSPQRERRRKK; for H9N2 it was INRTFKPLIGPRPLVNGLQG and SLKLAVGLRNVPARSSR. The discontinuous epitopes of NA of H5N1 and H9N2 were identified at various regions of the protein structure spanning from amino acid residue positions 90 to 449 and 107 to 469, respectively. Similarly, the discontinuous epitopes of HA of H5N1 and H9N2 were identified in the amino acid residue positions 27 to 517 and 136 to 521, respectively. This study has identified potential and highly immunogenic linear and conformational B-cell epitopes towards developing a vaccine against AIV both for human and poultry use.

Transient antibody-antigen interactions mediate the strain-specific recognition of a conserved malaria epitope

Transient interactions in which binding partners retain substantial conformational disorder play an essential role in regulating biological networks, challenging the expectation that specificity demands structurally defined and unambiguous molecular interactions. The monoclonal antibody 6D8 recognises a completely conserved continuous nine-residue epitope within the intrinsically disordered malaria antigen, MSP2, yet it has different affinities for the two allelic forms of this antigen. NMR chemical shift perturbations, relaxation rates and paramagnetic relaxation enhancements reveal the presence of transient interactions involving polymorphic residues immediately C-terminal to the structurally defined epitope. A combination of these experimental data with molecular dynamics simulations shows clearly that the polymorphic C-terminal extension engages in multiple transient interactions distributed across much of the accessible antibody surface. These interactions are determined more by topographical features of the antibody surface than by sequence-specific interactions. Thus, specificity arises as a consequence of subtle differences in what are highly dynamic and essentially non-specific interactions.