Characterization of a region involved in binding of measles virus H protein and its receptor SLAM (CD150)

Prediction of the Potential Host of Peste Des Petits Ruminants Virus by the Least Common Amino Acid Pattern in SLAM Receptor

Peste-des-Petits Ruminants Virus (PPRV) causes a highly contagious and severe infectious disease known as Peste-des-Petits Ruminants (PPR), resulting in significant mortality in both domestic and wild ruminants. An in-depth understanding of the molecular relationship between PPRV and susceptible hosts is essential for the prevention of PPR. The signaling lymphocytic-activation molecule (SLAM) acts as a key receptor in susceptible host species, mediating interactions with PPRV and triggering PPR in ruminants. This study offers an in-depth analysis of PPRV-susceptible host species as well as the identified SLAM amino acid sequences to date. Investigation reveals that nine families-Bovidae, Camelidae, Cervidae, Elephantidae, Suidae, Felidae, Canidae, Muridae, and Ceratopogonidae-have been affected by PPRV infection. Furthermore, a bioinformatics-based approach was proposed to screen the least common amino acid patterns (LCAP) in important SLAM receptor regions of known PPRV-susceptible species. Research findings reveal that 14 least common amino acid sites (LCAS) in SLAM amino acid sequences (I61, I63, S60, S70, K76, K78, I79, S81, L82, E123, N125, S127, V128, and F131) exhibit a prevalent similarity to LCAP across all known susceptible species. Comparative analysis of these 14 LCAP with SLAM nucleotide sequences from unknown susceptible ruminants to identify species at heightened risk of PPRV. In the result, 48 species from 20 different families across six orders were at potential risk of being infected with PPRV. This exploration suggests the feasibility of assessing potential hosts at high risk of PPRV infection through the LCAS screening technique. Moreover, it offers a means to anticipate and issue warnings regarding the likelihood of interspecies transmission. In conclusion, this study integrates molecular biology and bioinformatics, shedding light on PPRV infection dynamics and paving the way for predictive strategies to prevent the spread of this devastating disease among ruminant populations.

Identification of amino acid residues involved in the interaction between peste-des-petits-ruminants virus haemagglutinin protein and cellular receptors

Peste-des-petits-ruminants virus (PPRV) haemagglutinin (H) protein mediates binding to cellular receptors and then initiates virus entry. To identify the key residues of PPRV H (Hv) protein of the Nigeria 75/1 strain involved in binding to receptors, interaction of the Hv and mutated Hv (mHv) proteins with receptors (SLAM and Nectin 4) and their mutants (mSLAM1, mSLAM2, mSLAM3 and mNectin 4) was investigated using surface plasmon resonance imaging (SPRi) and coimmunoprecipitation (co-IP) assays. The results showed that the Hv protein failed to interact with mSLAM3, but interacted at a strong or medium intensity with SLAM, mSLAM2, Nectin 4 and mNectin 4, and at a low level with mSLAM1. The mHv protein was unable to interact with SLAM and its mutants, but bound to Nectin 4 and mNectin 4 with medium and weak intensity, respectively. Further analysis showed that the Hv protein could precipitate mSLAM1, mSLAM2 and mNectin 4, but not mSLAM3. The mHv protein failed to coprecipitate with SLAM and its mutants. The binding activities of mNectin 4 and Nectin 4 to mHv were less than 30.36 and 51.94 % of the wild-type levels, respectively. Based on the results obtained, amino acids at positions R389, L464, I498, R503, R533, Y541, Y543, F552 and Y553 of H protein and I61, H62, L64, K76, K78, E123, H130, I210, A211, S226 and R227 in SLAM were identified to be essential for the specificity of H-SLAM interaction, while the critical residues of H-Nectin 4 interaction require further study. These findings would improve our understanding of the invasive mechanisms of PPRV.

Regulatory Role of the Morbillivirus Attachment Protein Head-to-Stalk Linker Module in Membrane Fusion Triggering

Morbillivirus (e.g., measles virus [MeV] and canine distemper virus [CDV]) host cell entry is coordinated by two interacting envelope glycoproteins, namely, an attachment (H) protein and a fusion (F) protein. The ectodomain of H proteins consists of stalk, connector, and head domains that assemble into functional noncovalent dimer-of-dimers. The role of the C-terminal module of the H-stalk domain (termed linker) and the connector, although putatively able to assume flexible structures and allow receptor-induced structural rearrangements, remains largely unexplored. Here, we carried out a nonconservative mutagenesis scan analysis of the MeV and CDV H-linker/connector domains. Our data demonstrated that replacing isoleucine 146 in H-linker (H-I146) with any charged amino acids prevented virus-mediated membrane fusion activity, despite proper trafficking of the mutants to the cell surface and preserved binding efficiency to the SLAM/CD150 receptor. Nondenaturing electrophoresis revealed that these charged amino acid changes led to the formation of irregular covalent H tetramers rather than functional dimer-of-dimers formed when isoleucine or other hydrophobic amino acids were present at residue position 146. Remarkably, we next demonstrated that covalent H tetramerization per se was not the only mechanism preventing F activation. Indeed, the neutral glycine mutant (H-I146G), which exhibited strong covalent tetramerization propensity, maintained limited fusion promotion activity. Conversely, charged H-I146 mutants, which additionally carried alanine substitution of natural cysteines (H-C139A and H-C154A) and thus were unable to form covalently linked tetramers, were fusion activation defective. Our data suggest a dual regulatory role of the hydrophobic residue at position 146 of the morbillivirus head-to-stalk H-linker module: securing the assembly of productive dimer-of-dimers and contributing to receptor-induced F-triggering activity.IMPORTANCE MeV and CDV remain important human and animal pathogens. Development of antivirals may significantly support current global vaccination campaigns. Cell entry is orchestrated by two interacting glycoproteins (H and F). The current hypothesis postulates that tetrameric H ectodomains (composed of stalk, connector, and head domains) undergo receptor-induced rearrangements to productively trigger F; these conformational changes may be regulated by the H-stalk C-terminal module (linker) and the following connector domain. Mutagenesis scan analysis of both microdomains revealed that replacing amino acid 146 in the H-linker region with nonhydrophobic residues produced covalent H tetramers which were compromised in triggering membrane fusion activity. However, these mutant proteins retained their ability to traffic to the cell surface and to bind to the virus receptor. These data suggest that the morbillivirus linker module contributes to the folding of functional pre-F-triggering H tetramers. Furthermore, such structures might be critical to convert receptor engagement into F activation.

Hemagglutinin protein of measles virus induces apoptosis of HeLa cells via both extrinsic and intrinsic pathways

In this study, we investigated the potential for different components of the measles virus (MV) to induce apoptosis of HeLa cells and explored the apoptotic molecular mechanisms. After testing the 2 envelope glycoproteins hemagglutinin (H) and fusion (F), we found that MV H alone was sufficient to induce the apoptosis of HeLa cells, whereas MV F did not. MV F also had no influence on MV-H-mediated apoptosis. MV H could induce cellular apoptosis in HeLa cells through its interaction with the cellular receptor CD46 via both the TRAIL-mediated extrinsic pathway and the mitochondria-controlled intrinsic pathway, and that cross talk between these 2 pathways occurred during the process. These findings extend the functions of MV envelope glycoproteins in the pathogenesis of MV infection and suggest that MV H may be a potential therapeutic in the treatment of some cancers.

Canine distemper viruses expressing a hemagglutinin without N-glycans lose virulence but retain immunosuppression

Paramyxovirus glycoproteins are posttranslationally modified by the addition of N-linked glycans, which are often necessary for correct folding, processing, and cell surface expression. To establish the contribution of N glycosylation to morbillivirus attachment (H) protein function and overall virulence, we first determined the use of the potential N-glycosylation sites in the canine distemper virus (CDV) H proteins. Biochemical characterization revealed that the three sites conserved in all strains were N glycosylated, whereas only two of the up to five additional sites present in wild-type strains are used. A wild-type virus with an H protein reproducing the vaccine strain N-glycosylation pattern remained lethal in ferrets but with a prolonged course of disease. In contrast, introduction of the vaccine H protein in the wild-type context resulted in complete attenuation. To further characterize the role of N glycosylation in CDV pathogenesis, the N-glycosylation sites of wild-type H proteins were successively deleted, including a nonstandard site, to ultimately generate a nonglycosylated H protein. Despite reduced expression levels, this protein remained fully functional. Recombinant viruses expressing N-glycan-deficient H proteins no longer caused disease, even though their immunosuppressive capacities were retained, indicating that reduced N glycosylation contributes to attenuation without affecting immunosuppression.

Variations in measles vaccine–specific humoral immunity by polymorphisms in SLAM and CD46 measles virus receptors

BACKGROUND

Measles infection requires 2 cellular receptors, signaling lymphocyte activation molecule (SLAM) and CD46. Known and novel single nucleotide polymorphisms (SNPs) in SLAM and CD46 genes might influence the immune response to measles vaccine.

OBJECTIVE

We sought to identify SNP associations in SLAM and CD46 genes with variations in measles antibody response.

METHODS

We genotyped known SNPs in SLAM and CD46 genes in 339 subjects vaccinated with 2 doses of measles-mumps-rubella vaccine. We also sequenced the measles virus-binding domains of SLAM and CD46 to identify novel SNPs.

RESULTS

Increased representation of minor alleles for rs3796504 and rs164288 in the SLAM gene was associated with an allele dose-related decrease (4-fold) in measles-specific antibodies. Heterozygous genotype TC for rs12076998 located in the untranslated region 33 bp upstream of the measles virus-binding domain of the SLAM gene was associated with higher median antibody levels (1991 vs 1467 IU/L, P = .01) compared with wild-type TT. Within the CD46 gene, the minor allele C for intronic SNP (rs11118580) was associated with an allele dose-related decrease in measles antibodies (1072 vs 1795 IU/L, P < .01). Decreases in minor allele counts for rs3796504, rs164288, and rs1118580 demonstrated a significant (P < .001) additive effect on measles-specific antibodies.

CONCLUSION

Our data suggest that specific SNPs present in both the SLAM and CD46 genes are associated with measurable and significant variations in antibody response after measles vaccination.

CLINICAL IMPLICATIONS

Understanding the immunogenetics of measles vaccine receptors is important to better understand variations in immune responses to vaccines and to design better vaccines.

Identification of Hendra virus G glycoprotein residues that are critical for receptor binding

Hendra virus (HeV) is an emerging paramyxovirus capable of infecting and causing disease in a variety of mammalian species, including humans. The virus infects its host cells through the coordinated functions of its fusion (F) and attachment (G) glycoproteins, the latter of which is responsible for binding the virus receptors ephrinB2 and ephrinB3. In order to identify the receptor binding site, a panel of G glycoprotein constructs containing mutations was generated using an alanine-scanning mutagenesis strategy. Based on a predicted G structure, charged amino acids residing in regions that could be homologous to those in the measles virus H attachment glycoprotein known to be involved in its protein receptor interaction were targeted. Using a coprecipitation-based assay, seven single-amino-acid substitutions in HeV G were identified as having significantly impaired binding to both the ephrinB2 and ephrinB3 viral receptors: D257A, D260A, G439A, K443A, G449A, K465A, and D468A. The impairment of receptor interaction conferred a concomitant diminution in their abilities to promote membrane fusion when coexpressed with F. The G glycoprotein mutants were also recognized by three or more conformation-dependent monoclonal antibodies of a panel of five, were expressed on the cell surface, and retained their abilities to bind and coprecipitate F. Interestingly, some of these mutant G glycoproteins coprecipitated with F more efficiently than wild-type G. Taken together, these data provide strong biochemical and functional evidence that some of these residues could be part of a conformation-dependent, discontinuous, and overlapping ephrinB2 and -B3 binding domain within the HeV G glycoprotein.

Identification of Amino Acid Residues Involved in the Interaction between Measles Virus Haemagglutin (MVH) and Its Human Cell Receptor(Signaling Lymphocyte Activation Molecule, SLAM)

Signaling lymphocyte activation molecule (SLAM; also known as CD150) is a newly identified cellular receptor for measles virus (MV). The interaction between MV Haemagglutin (MVH) and SLAM is an initial step for MV entry. We have identified several novel SLAM binding sites at residues S429, T436 and H437 of MVH protein and MVH mutants in these residues dramatically decrease the ability to interaction with the cell surface SLAM and fail to coprecipitation with SLAM in vivo as well as malfunction in syncytium formation. At the same time, K58, S59 and H61 of SLAM was also identified to be critical for MVH and SLAM binding. Further, these residues may be useful targets for the development of measles therapy.

Identification of one peptide which inhibited infectivity of avian infectious bronchitis virus in vitro

Purified avian infectious bronchitis virus (IBV) was used to screen a random phage display peptide library. After the fourth panning, 10 positive phages were sequenced and characterized. The phages specifically inhibited IBV infectivity in HeLa cells and blocked IBV haemagglutination. One linear peptide "GSH HRH VHS PFV" from the positive phages with the highest neutralization titer was synthesized and this peptide inhibited IBV infection in HeLa as well. The results may contribute to development of antiviral therapeutics for IBV and studying the determinants for viral and cell interaction.

Location of, immunogenicity of and relationships between neutralization epitopes on the attachment protein (G) of Hendra virus

Epitopes involved in a protective immune response to Hendra virus (HeV) (Henipavirus, Paramxyoviridae) were investigated by generating five neutralizing monoclonal antibodies (mAbs) to the virus attachment protein (G) of HeV (HeV G) and sequencing of the G gene of groups of neutralization-escape variants selected with each mAb. Amino acid substitutions occurred at eight distinct sites on HeV G. Relationships between these sites were investigated in binding and neutralization assays using heterologous combinations of variants and mAbs. The sites were also mapped to a proposed structural model for the attachment proteins of Paramyxoviridae. Their specific locations and the nature of their interactions with the mAb panel provided the first functional evidence that HeV G in fact resembled the proposed structure. Four sites (aa 183-185, 417, 447 and 570) contributed to a major discontinuous epitope, on the base of the globular head, that was similar to immunodominant virus neutralization sites found in other paramyxoviruses. Amino acid similarity between HeV and Nipah virus was relatively highly conserved at these sites but decreased significantly at the other sites identified in this study. These included another discontinuous epitope on the base of the head region defined by sites aa 289 and 324 and well separated epitopes on the top of the head at sites aa 191-195 and 385-356. The latter epitope corresponded to immunodominant neutralization sites found in Rinderpest virus and Measles virus.

Identification of Three gp350/220 Regions Involved in Epstein-Barr Virus Invasion of Host Cells

Epstein-Barr virus (EBV) invasion of B-lymphocytes involves EBV gp350/220 binding to B-lymphocyte CR2. The anti-gp350 monoclonal antibody (mAb)-72A1 Fab inhibits this binding and therefore blocks EBV invasion of target cells. However, gp350/220 regions interacting with mAb 72A1 and involved in EBV invasion of target cells have not yet been identified. This work reports three gp350/220 regions, defined by peptide 11382, 11389, and 11416 sequences, that are involved in EBV binding to B-lymphocytes. Peptides 11382, 11389, and 11416 bound to CR2(+) but not to CR2(-) cells, inhibited EBV invasion of cord blood lymphocytes (CBLs), were recognized by mAb 72A1, and inhibited mAb 72A1 binding to EBV. Peptides 11382 and 11416 binding to peripheral blood lymphocytes (PBLs) induced interleukin-6 protein synthesis in these cells, this phenomenon being inhibited by mAb 72A1. The same behavior has been reported for gp350/220 binding to PBLs. Anti-peptide 11382, 11389, and 11416 antibodies inhibited EBV binding and EBV invasion of PBLs and CBLs. Peptide 11382, 11389, and 11416 sequences presented homology with the C3dg regions coming into contact with CR2 (C3dg and gp350 bound to similar CR2 regions). These peptides could be used in designing strategies against EBV infection.

Interactions among measles virus hemagglutinin, fusion protein and cell receptor signaling lymphocyte activation molecule (SLAM) indicating a new fusion-trimer model

For measles viruses, fusion on the cell membrane is an important initial step in the entry into the infected cells. The recent research indicated that hemagglutinin firstly leads the conformational changes in the fusion protein then co-mediates the membrane fusion. In the work, we use the co-immunoprecipitation and pull-down techniques to identify the interactions among fusion protein, hemagglutinin and signaling lymphocyte activation molecule (SLAM), which reveal that the three proteins can form a functional complex to mediate the SLAM-dependent fusion. Moreover, under the confocal microscope, fusion protein and hemagglutinin protein can show the cocapping mediated by the SLAM. So fusion protein not only is involved in the fusion but also might directly interact with the SLAM to be a new fusion-trimer model, which might account for the infection mechanism of measles virus.

Is mRNA and protein level of CD46 altered in measles virus vaccine strain S191-infected cells?

Previous research showed that the expression of measles virus receptor CD46 was downregulated after expression of measles virus hemagglutinin protein on the surface of the virus infected cell or triggered by infected cell-to-cell contact. We reported here that the mRNA level of CD46 in MV infected cells was not changed which was tested by real-time quantitative PCR. To further analyse the surface expression alteration of CD46 after MV infection, flow cytometric analysis and indirect immunofluorescence were used to detect the protein level of CD46. Altogether, our results provided a demonstration that the expression of CD46 was not downregulated by the infection of MV strain S191 both on mRNA level and cellular surface protein level. Previous results reported that the "downregulation" of CD46 expression on the cell surface may take place because H protein masks the antibody recognition site on CD46 which results in "downregulation" of the expression of CD46.

Identifying gp85-regions involved in Epstein-Barr virus binding to B-lymphocytes

Epstein-Barr virus lacking glycoprotein gp85 cannot infect B-cells and epithelial cells. The gp85 belongs to the molecular complex required for virus invasion of B-lymphocyte or epithelial cells. Moreover, there is evidence that gp85 is necessary for virus attachment to epithelial cells. Thirty-six peptides from the entire gp85-sequence were tested in epithelial and lymphoblastoid cell line binding assays to identify gp85-regions involved in virus-cell interaction. Five of these peptides presented high binding activity to Raji, Ramos, P3HR-1, and HeLa cells, but not to erythrocytes; Raji-cell affinity constants were between 80 and 140nM. Of these five peptides, 11435 ((181)TYKRVTEKGDEHVLSLVFGK(200)), 11436 ((201)TKDLPDLRGPFSYPSLTSAQ(220)), and 11438 ((241)YFVPNLKDMFSRAVTMTAAS(260)) bound to a 65kDa protein on Raji-cell surface. These peptides and antibodies induced by them (recognising live EBV-infected cells) inhibited Epstein-Barr virus interaction with cord blood lymphocytes. It is thus probable that gp85-regions defined by peptides 11435, 11436, and 11438 are involved in EBV invasion of B-lymphocytes.