Structure of the measles virus hemagglutinin bound to its cellular receptor SLAM

Detailed analysis of low temperature inactivation of respiratory syncytial virus

Our previous findings indicated that many respiratory syncytial virus (RSV) isolates are unstable at 4 °C compared to 20 °C. Some of the strains completely lose infectivity after 24 h at 4 °C. This study analyzed the inactivation process at 4 °C using a representative strain, RSV/Sendai/851/13. After 24 h of storage at 4 °C, the virus was completely inactivated but retained its ability to attach to and to be taken into host cells. It suggested a reduced fusion ability between the viral and cellular membranes. During storage at 4 °C, the RSV fusion (F) protein underwent a conformational change and was no longer recognized by pre-fusion form-specific antibodies. When the RSV/Sendai/851/13 strain was passaged at 4 °C, a variant with an amino acid substitution, I148T, in the F protein fusion peptide was selected. Also, an amino acid change in G protein demonstrating stability at low temperatures was obtained. These results show that the inactivation of RSV at 4 °C is due to the loss of membrane fusion activity in the F protein, which cannot maintain its pre-fusion state at 4 °C.

Unveiling the affinity-stability relationship in anti-measles virus antibodies: a computational approach for hotspots prediction

Recent years have seen an uptick in the use of computational applications in antibody engineering. These tools have enhanced our ability to predict interactions with antigens and immunogenicity, facilitate humanization, and serve other critical functions. However, several studies highlight the concern of potential trade-offs between antibody affinity and stability in antibody engineering. In this study, we analyzed anti-measles virus antibodies as a case study, to examine the relationship between binding affinity and stability, upon identifying the binding hotspots. We leverage in silico tools like Rosetta and FoldX, along with molecular dynamics (MD) simulations, offering a cost-effective alternative to traditional in vitro mutagenesis. We introduced a pattern in identifying key residues in pairs, shedding light on hotspots identification. Experimental physicochemical analysis validated the predicted key residues by confirming significant decrease in binding affinity for the high-affinity antibodies to measles virus hemagglutinin. Through the nature of the identified pairs, which represented the relative hydropathy of amino acid side chain, a connection was proposed between affinity and stability. The findings of the study enhance our understanding of the interactions between antibody and measles virus hemagglutinin. Moreover, the implications of the observed correlation between binding affinity and stability extend beyond the field of anti-measles virus antibodies, thereby opening doors for advancements in antibody research.

Vaccine-induced neutralizing antibodies bind to the H protein of a historical measles virus

Measles is a highly contagious airborne viral disease. It can lead to serious complications and death and is preventable by vaccination. The live-attenuated measles vaccine (LAMV) derived from a measles virus (MV) isolated in 1954 has been in use globally for six decades and protects effectively by providing a durable humoral and cell-mediated immunity. Our study addresses the temporal stability of epitopes on the viral surface glycoprotein hemagglutinin (H) which is the major target of MV-neutralizing antibodies. We investigated the binding of seven vaccine-induced MV-H-specific monoclonal antibodies (mAbs) to cell-free synthesized MV-H proteins derived from the H gene sequences obtained from a lung specimen of a fatal case of measles pneumonia in 1912 and an isolate from a current case. The binding of four out of seven mAbs to the H protein of both MV strains provides evidence of epitopes that are stable for more than 100 years. The binding of the universally neutralizing mAbs RKI-MV-12b and RKI-MV-34c to the H protein of the 1912 MV suggests the long-term stability of highly conserved epitopes on the MV surface.

Virological characteristics of the SARS-CoV-2 Omicron XBB.1.5 variant

Circulation of SARS-CoV-2 Omicron XBB has resulted in the emergence of XBB.1.5, a new Variant of Interest. Our phylogenetic analysis suggests that XBB.1.5 evolved from XBB.1 by acquiring the S486P spike (S) mutation, subsequent to the acquisition of a nonsense mutation in ORF8. Neutralization assays showed similar abilities of immune escape between XBB.1.5 and XBB.1. We determine the structural basis for the interaction between human ACE2 and the S protein of XBB.1.5, showing similar overall structures between the S proteins of XBB.1 and XBB.1.5. We provide the intrinsic pathogenicity of XBB.1 and XBB.1.5 in hamsters. Importantly, we find that the ORF8 nonsense mutation of XBB.1.5 resulted in impairment of MHC suppression. In vivo experiments using recombinant viruses reveal that the XBB.1.5 mutations are involved with reduced virulence of XBB.1.5. Together, our study identifies the two viral functions defined the difference between XBB.1 and XBB.1.5.

Neutralizing Antibody Response to Genotypically Diverse Measles Viruses in Clinically Suspected Measles Cases

The neutralizing antibody (Nt-Ab) response to vaccine and wild-type measles viruses (MeV) was studied in suspected measles cases reported during the years 2012-2016. The neutralization activity against MeV A, D4 and D8 genotypes was studied on sera (Panel A; n = 68 (measles-immunized) and Panel B; n = 50 (unvaccinated)) that were either laboratory confirmed or not confirmed by the presence of IgM antibodies. Additionally, the Nt-Ab response in Panel A was measured against the MeV vaccine and four wild-type viruses. Neutralization results were compared using homology modeling and molecular dynamics simulation (MDS) of MeV-hemagglutinin (H) and fusion (F) proteins. Overall, the Nt-Ab titres for MeV-A were found to be significantly lower than MeV-D4 and MeV-D8 viruses for Panel A. No major difference was noted in Nt-Ab titres between MeV-D8 viruses (Jamnagar and New Delhi), whereas MeV-D4 (Sindhudurg and Bagalkot (BGK) viruses) showed significant differences between Nt-Ab titres for Panel B. Interestingly, the substitutions observed in epitopes of H-protein, L249P and G316A are observed to be unique to MeV-BGK. MDS of H-protein revealed significant fluctuations in neutralizing epitopes due to L249P substitution. The majority of the clinically suspected cases showed Nt-Abs to MeV wild-types. Higher IgG antibody avidity and Nt-Ab titres were noted in IgM-negatives than in IgM-positives cases, indicating reinfection or breakthrough. MDS revealed reduced neutralization due to decreased conformational flexibility in the H-epitope.

Crystal structure and solution state of the C-terminal head region of the narmovirus receptor binding protein

IMPORTANCE

Genetically diverse paramyxoviruses are united in their presentation of a receptor-binding protein (RBP), which works in concert with the fusion protein to facilitate host-cell entry. The C-terminal head region of the paramyxoviral RBP, a primary determinant of host-cell tropism and inter-species transmission potential, forms structurally distinct classes dependent upon protein and glycan receptor specificity. Here, we reveal the architecture of the C-terminal head region of the RBPs from Nariva virus (NarV) and Mossman virus (MosV), two archetypal rodent-borne paramyxoviruses within the recently established genus Narmovirus, family Paramyxoviridae. Our analysis reveals that while narmoviruses retain the general architectural features associated with paramyxoviral RBPs, namely, a six-bladed β-propeller fold, they lack the structural motifs associated with known receptor-mediated host-cell entry pathways. This investigation indicates that the RBPs of narmoviruses exhibit pathobiological features that are distinct from those of other paramyxoviruses.

Biophysical characterization of the cetacean morbillivirus haemagglutinin glycoprotein

Cetacean morbillivirus (CeMV) is an enveloped, non-segmented, negative-stranded RNA virus that infects marine mammals, spreading across species and causing lethal disease outbreaks worldwide. Among the eight proteins encoded by the CeMV genome, the haemagglutinin (H) glycoprotein is responsible for the virus attachment to host cell receptors. CeMV H represents an attractive target for antiviral and diagnostic research, yet the elucidation of the molecular mechanisms underlying its role in infection and inter-species transmission was hampered thus far due to the unavailability of recombinant versions of the protein. Here we present the cloning, expression and purification of a recombinant CeMV H ectodomain (rH-ecto), providing an initial characterization of its biophysical and structural properties. Sodium dodecyl sulphate - polyacrylamide gel electrophoresis (PAGE) combined to Western blot analysis and periodic acid Schiff assay showed that CeMV rH-ecto is purifiable at homogeneity from insect cells as a secreted, soluble and glycosylated protein. Miniaturized differential scanning fluorimetry, Blue Native PAGE and size exclusion chromatography coupled to multiangle light scattering revealed that CeMV rH-ecto is globularly folded, thermally stable and exists in solution in the oligomeric states of dimer and multiple of dimers. Furthermore, negative stain electron microscopy single particle analysis allowed us to delineate a low-resolution molecular architecture of the CeMV rH-ecto dimer, which recapitulates native assemblies from other morbilliviral H proteins, such as those from measles virus and canine distemper virus. This set of experiments by orthogonal techniques validates the CeMV rH-ecto as an experimental model for future biochemical studies on its structure and functions.

Development of a monoclonal antibody recognizing novel linear neutralizing epitope on H protein of canine distemper virus vaccine strains (America-1 genotype)

Canine distemper virus (CDV) is an economically important virus responsible for canine distemper (CD), a highly contagious disease that afflicts various animal species worldwide. The hemagglutinin (H) protein is the major neutralizing target of virus. Therefore, it is often considered as immunogen to prepare neutralizing antibodies. The accurate identification of neutralizing epitope will provide important antigenic information and extend the knowledge of mechanisms of virus neutralization. In this study, we generated a neutralizing monoclonal antibody (mAb) 4C6 against CDV H protein, and defined the minimal linear epitope 238DIEREFDT245, which was highly conserved in America-1 genotype of CDV strains (vaccines). The mAb 4C6 could not react with a CDV strain that had two substitutions of D238Y and R241G in the epitope, which appeared in most CDV strains of the other genotypes. Besides, a few different amino acid mutations in the epitope were also included. Collectively, the epitope 238DIEREFDT245 was variable in the other genotypes of CDV strains. The epitope 238DIEREFDT245 was exposed to the surface of CDV H protein, showing good antigenicity. These data will provide insights into structure, function and antigenicity of H protein and lay the foundation for the development of diagnostic technologies and vaccine design for CDV.

Suppression of viral RNA polymerase activity is necessary for persistent infection during the transformation of measles virus into SSPE virus

Subacute sclerosing panencephalitis (SSPE) is a fatal neurodegenerative disease caused by measles virus (MV), which typically develops 7 to 10 years after acute measles. During the incubation period, MV establishes a persistent infection in the brain and accumulates mutations that generate neuropathogenic SSPE virus. The neuropathogenicity is closely associated with enhanced propagation mediated by cell-to-cell fusion in the brain, which is principally regulated by hyperfusogenic mutations of the viral F protein. The molecular mechanisms underlying establishment and maintenance of persistent infection are unclear because it is impractical to isolate viruses before the appearance of clinical signs. In this study, we found that the L and P proteins, components of viral RNA-dependent RNA polymerase (RdRp), of an SSPE virus Kobe-1 strain did not promote but rather attenuated viral neuropathogenicity. Viral RdRp activity corresponded to F protein expression; the suppression of RdRp activity in the Kobe-1 strain because of mutations in the L and P proteins led to restriction of the F protein level, thereby reducing cell-to-cell fusion mediated propagation in neuronal cells and decreasing neuropathogenicity. Therefore, the L and P proteins of Kobe-1 did not contribute to progression of SSPE. Three mutations in the L protein strongly suppressed RdRp activity. Recombinant MV harboring the three mutations limited viral spread in neuronal cells while preventing the release of infectious progeny particles; these changes could support persistent infection by enabling host immune escape and preventing host cell lysis. Therefore, the suppression of RdRp activity is necessary for the persistent infection of the parental MV on the way to transform into Kobe-1 SSPE virus. Because mutations in the genome of an SSPE virus reflect the process of SSPE development, mutation analysis will provide insight into the mechanisms underlying persistent infection.

NgR1 binding to reovirus reveals an unusual bivalent interaction and a new viral attachment protein

Nogo-66 receptor 1 (NgR1) binds a variety of structurally dissimilar ligands in the adult central nervous system to inhibit axon extension. Disruption of ligand binding to NgR1 and subsequent signaling can improve neuron outgrowth, making NgR1 an important therapeutic target for diverse neurological conditions such as spinal crush injuries and Alzheimer's disease. Human NgR1 serves as a receptor for mammalian orthoreovirus (reovirus), but the mechanism of virus-receptor engagement is unknown. To elucidate how NgR1 mediates cell binding and entry of reovirus, we defined the affinity of interaction between virus and receptor, determined the structure of the virus-receptor complex, and identified residues in the receptor required for virus binding and infection. These studies revealed that central NgR1 surfaces form a bridge between two copies of viral capsid protein σ3, establishing that σ3 serves as a receptor ligand for reovirus. This unusual binding interface produces high-avidity interactions between virus and receptor to prime early entry steps. These studies refine models of reovirus cell-attachment and highlight the evolution of viruses to engage multiple receptors using distinct capsid components.

Metagenomics-enabled reverse-genetics assembly and characterization of myotis bat morbillivirus

Morbilliviruses are among the most contagious viral pathogens of mammals. Although previous metagenomic surveys have identified morbillivirus sequences in bats, full-length morbilliviruses from bats are limited. Here we characterize the myotis bat morbillivirus (MBaMV) from a bat surveillance programme in Brazil, whose full genome was recently published. We demonstrate that the fusion and receptor binding protein of MBaMV utilize bat CD150 and not human CD150, as an entry receptor in a mammalian cell line. Using reverse genetics, we produced a clone of MBaMV that infected Vero cells expressing bat CD150. Electron microscopy of MBaMV-infected cells revealed budding of pleomorphic virions, a characteristic morbillivirus feature. MBaMV replication reached 103-105 plaque-forming units ml-1 in human epithelial cell lines and was dependent on nectin-4. Infection of human macrophages also occurred, albeit 2-10-fold less efficiently than measles virus. Importantly, MBaMV is restricted by cross-neutralizing human sera elicited by measles, mumps and rubella vaccination and is inhibited by orally bioavailable polymerase inhibitors in vitro. MBaMV-encoded P/V genes did not antagonize human interferon induction. Finally, we show that MBaMV does not cause disease in Jamaican fruit bats. We conclude that, while zoonotic spillover into humans may theoretically be plausible, MBaMV replication would probably be controlled by the human immune system.

Interaction of the Hemagglutinin Stalk Region with Cell Adhesion Molecule (CADM) 1 and CADM2 Mediates the Spread between Neurons and Neuropathogenicity of Measles Virus with a Hyperfusogenic Fusion Protein

Measles virus (MeV), the causative agent of measles, is an enveloped RNA virus of the family Paramyxoviridae, which remains an important cause of childhood morbidity and mortality. MeV has two envelope glycoproteins, the hemagglutinin (H) and fusion (F) proteins. During viral entry or virus-mediated fusion between infected cells and neighboring susceptible cells, the head domain of the H protein initially binds to its receptors, signaling lymphocytic activation molecule family member 1 (SLAM) and nectin-4, and then the stalk region of the H protein transmits the fusion-triggering signal to the F protein. MeV may persist in the human brain and cause a fatal neurodegenerative disease, subacute sclerosing panencephalitis (SSPE). Recently, we showed, using in vitro cell culture, that cell adhesion molecule (CADM) 1 and CADM2 are host factors that trigger hyperfusogenic mutant F proteins, causing cell-to-cell fusion and the transfer of the MeV genome between neurons. Unlike conventional receptors, CADM1 and CADM2 interact in cis (on the same membrane) with the H protein and then trigger membrane fusion. Here, we show that alanine substitutions in part of the stalk region (positions 171-175) abolish the ability of the H protein to mediate membrane fusion triggered by CADM1 and CADM2, but not by SLAM. The recombinant hyperfusogenic MeV carrying this mutant H protein loses its ability to spread in primary mouse neurons as well as its neurovirulence in experimentally infected suckling hamsters. These results indicate that CADM1 and CADM2 are key molecules for MeV propagation in the brain and its neurovirulence in vivo. IMPORTANCE Measles is an acute febrile illness with skin rash. Despite the availability of highly effective vaccines, measles is still an important cause of childhood morbidity and mortality in many countries. The World Health Organization estimates that more than 120,000 people died from measles worldwide in 2021. Measles virus (MeV), the causative agent of measles, can also cause a fatal progressive neurological disorder, subacute sclerosing panencephalitis (SSPE), several years after acute infection. There is currently no effective treatment for this disease. In this study, using recombinant MeVs with altered receptor usage patterns, we show that cell adhesion molecule (CADM) 1 and CADM2 are host factors critical for MeV spread in neurons and its neurovirulence. These findings further our understanding of the molecular mechanism of MeV neuropathogenicity.

SLAMF7 regulates the inflammatory response in macrophages during polymicrobial sepsis

Uncontrolled inflammation occurred in sepsis results in multiple organ injuries and shock, which contributes to the death of patients with sepsis. However, the regulatory mechanisms that restrict excessive inflammation are still elusive. Here, we identified an Ig-like receptor called signaling lymphocyte activation molecular family 7 (SLAMF7) as a key suppressor of inflammation during sepsis. We found that the expression of SLAMF7 on monocytes/macrophages was significantly elevated in patients with sepsis and in septic mice. SLAMF7 attenuated TLR-dependent MAPK and NF-κB signaling activation in macrophages by cooperating with Src homology 2-containing inositol-5'‑phosphatase 1 (SHIP1). Furthermore, SLAMF7 interacted with SHIP1 and TNF receptor-associated factor 6 (TRAF6) to inhibit K63 ubiquitination of TRAF6. In addition, we found that tyrosine phosphorylation sites within the intracellular domain of SLAMF7 and the phosphatase domain of SHIP1 were indispensable for the interaction between SLAMF7, SHIP1, and TRAF6 and SLAMF7-mediated modulation of cytokine production. Finally, we demonstrated that SLAMF7 protected against lethal sepsis and endotoxemia by downregulating macrophage proinflammatory cytokines and suppressing inflammation-induced organ damage. Taken together, our findings reveal a negative regulatory role of SLAMF7 in polymicrobial sepsis, thus providing sights into the treatment of sepsis.

Molecular Modeling Identification of Key Secondary Metabolites from Xylopia aethiopica as Promising Therapeutics Targeting Essential Measles Viral Proteins

This study computationally screened three key compounds (vanillin (VAN), oxophoebine (OPB), and dihydrochalcone (DHC)) derived from Xylopia aethiopica (Guinea pepper), a medicinal plant with known antiviral activity, against key druggable measles virus (MV) proteins (fusion protein (FUP), haemagglutinin protein (HMG), and phosphoprotein (PSP)). Each molecular species was subjected to a 100 ns molecular dynamics (MD) simulation following docking, and a range of postdynamic parameters including free binding energy and pharmacokinetic properties were determined. The docking scores of the resulting OPB-FUP (-5.4 kcal/mol), OPB-HMG (-8.1 kcal/mol), and OPB-PSP (-8.0 kcal/mol) complexes were consistent with their respective binding energy values (-25.37, -28.74, and -40.68 kcal/mol), and higher than that of the reference standard, ribavirin (RBV) in each case. Furthermore, all the investigated compounds were thermodynamically compact and stable, especially HMG of MV, and this observation could be attributed to the resulting intermolecular interactions in each system. Overall, OPB may possess inhibitory properties against MV glycoproteins (FUP and HMG) and PSP that play important roles in the replication of MV and measles pathogenesis. While OPB could serve as a scaffold for the development of novel MV fusion and entry inhibitors, further in vitro and in vivo evaluation is highly recommended.

Paramyxoviruses from bats: changes in receptor specificity and their role in host adaptation

Global metagenomic surveys have revealed that bats host a diverse array of paramyxoviruses, including species from at least five major genera. An essential determinant of successful spillover is the entry of a virus into a new host. We evaluate the role of receptor usage in the zoonotic potential of bat-borne henipaviruses, morbilliviruses, pararubulaviruses, orthorubulaviruses, and jeilongviruses; successful spillover into humans depends upon compatibility of a respective viral attachment protein with its cognate receptor. We also emphasize the importance of postentry restrictions in preventing spillover. Metagenomics and characterization of newly identified paramyxoviruses have greatly improved our understanding of spillover determinants, allowing for better forecasts of which bat-borne viruses may pose the greatest risk for cross-species transmission into humans.

Structure and function of a novel lineage-specific neutralizing epitope on H protein of canine distemper virus

Canine distemper virus (CDV) infects many sensitive species worldwide and its host range is expanding. The hemagglutinin (H) protein, the major neutralizing target, binds to cellular receptors and subsequently triggers fusion for initial viral infection. So it's necessary to clarify the precise neutralizing epitopes of H protein and extend the knowledge of mechanisms of virus neutralization. In this study, a neutralizing monoclonal antibody (mAb) 2D12 against CDV H protein, which had different reactivity with different CDV strains, was generated and characterized. A series of truncated H proteins were screened to define the minimal linear epitope 238DIEREFD244 recognized by 2D12. Further investigation revealed that the epitope was highly conserved in America-1 vaccine lineage of CDV strains, but different substitutions in the epitope appeared in CDV strains of the other lineages and two substitutions (D238Y and R241G) caused the change of antigenicity. Thus, the epitope represents a novel lineage-specific neutralizing target on H protein of CDV for differentiation of America-1 vaccine lineage and the other lineages of CDV strains. The epitope was identified to localize at the surface of H protein in two different positions in a three-dimensional (3D) structure, but not at the position of the receptor-binding site (RBS), so the mAb 2D12 that recognized the epitope did not inhibit binding of H protein to the receptor. But mAb 2D12 interfered with the H-F interaction for inhibiting membrane fusion, suggesting that the mAb plays key roles for formation of H-F protein oligomeric structure. Our data will contribute to the understanding of the structure, function, and antigenicity of CDV H protein and mechanisms of virus neutralization.

A defined anthocyanin mixture sourced from bilberry and black currant inhibits Measles virus and various herpesviruses

Background

Anthocyanin-containing plant extracts and carotenoids, such as astaxanthin, have been well-known for their antiviral and anti-inflammatory activity, respectively. We hypothesised that a mixture of Ribes nigrum L. (Grossulariaceae) (common name black currant (BC)) and Vaccinium myrtillus L. (Ericaceae) (common name bilberry (BL)) extracts (BC/BL) with standardised anthocyanin content as well as single plant extracts interfered with the replication of Measles virus and Herpesviruses in vitro.

Methods

We treated cell cultures with BC/BL or defined single plant extracts, purified anthocyanins and astaxanthin in different concentrations and subsequently infected the cultures with the Measles virus (wild-type or vaccine strain Edmonston), Herpesvirus 1 or 8, or murine Cytomegalovirus. Then, we analysed the number of infected cells and viral infectivity and compared the data to non-treated controls.

Results

The BC/BL extract inhibited wild-type Measles virus replication, syncytia formation and cell-to-cell spread. This suppression was dependent on the wild-type virus-receptor-interaction since the Measles vaccine strain was unaffected by BC/BL treatment. Furthermore, the evidence was provided that the delphinidin-3-rutinoside chloride, a component of BC/BL, and purified astaxanthin, were effective anti-Measles virus compounds. Human Herpesvirus 1 and murine Cytomegalovirus replication was inhibited by BC/BL, single bilberry or black currant extracts, and the BC/BL component delphinidin-3-glucoside chloride. Additionally, we observed that BC/BL seemed to act synergistically with aciclovir. Moreover, BC/BL, the single bilberry and black currant extracts, and the BC/BL components delphinidin-3-glucoside chloride, cyanidin-3-glucoside, delphinidin-3-rutinoside chloride, and petunidin-3-galactoside inhibited human Herpesvirus 8 replication.

Conclusions

Our data indicate that Measles viruses and Herpesviruses are differentially susceptible to a specific BC/BL mixture, single plant extracts, purified anthocyanins and astaxanthin. These compounds might be used in the prevention of viral diseases and in addition to direct-acting antivirals, such as aciclovir.

Novel and classical morbilliviruses: Current knowledge of three divergent morbillivirus groups

Currently, seven species of morbillivirus have been classified. Six of these species (Measles morbillivirus, Rinderpest morbillivirus, Small ruminant morbillivirus, Canine morbillivirus, Phocine morbillivirus, and Cetacean morbillivirus) are highly infectious and cause serious systemic diseases in humans, livestock, domestic dogs, and wild animals. These species commonly use the host proteins signaling lymphocytic activation molecule (SLAM) and nectin-4 as receptors, and this usage contributes to their virulence. The seventh species (Feline morbillivirus: FeMV) is phylogenetically divergent from the six SLAM-using species. FeMV differs from the SLAM-using morbillivirus group in pathogenicity and infectivity, and is speculated to use non-SLAM receptors. Recently, novel species of morbilliviruses have been discovered in bats, rodents, and domestic pigs. Because the ability to use SLAM and nectin-4 is closely related to the infectivity and pathogenicity of morbilliviruses, investigation of the potential usage of these receptors is useful for estimating infectivity and pathogenicity. The SLAM-binding sites in the receptor-binding protein show high similarity among the SLAM-using morbilliviruses. This feature may help to estimate whether novel morbillivirus species can use SLAM as a receptor. A novel morbillivirus species isolated from wild mice diverged from the classified morbilliviruses in the phylogenetic tree, forming a third group separate from the SLAM-using morbillivirus group and FeMV. This suggests that the novel rodent morbillivirus may exhibit a different risk from the SLAM-using morbillivirus group, and analyses of its viral pathogenicity and infectivity toward humans are warranted.

FeMV is a cathepsin-dependent unique morbillivirus infecting the kidneys of domestic cats

Feline morbillivirus (FeMV) is a recently discovered pathogen of domestic cats and has been classified as a morbillivirus in the Paramyxovirus family. We determined the complete sequence of FeMV^US5 directly from an FeMV-positive urine sample without virus isolation or cell passage. Sequence analysis of the viral genome revealed potential divergence from characteristics of archetypal morbilliviruses. First, the virus lacks the canonical polybasic furin cleavage signal in the fusion (F) glycoprotein. Second, conserved amino acids in the hemagglutinin (H) glycoprotein used by all other morbilliviruses for binding and/or fusion activation with the cellular receptor CD150 (signaling lymphocyte activation molecule [SLAM]/F1) are absent. We show that, despite this sequence divergence, FeMV H glycoprotein uses feline CD150 as a receptor and cannot use human CD150. We demonstrate that the protease responsible for cleaving the FeMV F glycoprotein is a cathepsin, making FeMV a unique morbillivirus and more similar to the closely related zoonotic Nipah and Hendra viruses. We developed a reverse genetics system for FeMV^US5 and generated recombinant viruses expressing Venus fluorescent protein from an additional transcription unit located either between the phospho-protein (P) and matrix (M) genes or the H and large (L) genes of the genome. We used these recombinant FeMVs to establish a natural infection and demonstrate that FeMV causes an acute morbillivirus-like disease in the cat. Virus was shed in the urine and detectable in the kidneys at later time points. This opens the door for long-term studies to address the postulated role of this morbillivirus in the development of chronic kidney disease.

Virological characteristics of the SARS-CoV-2 Omicron BA.2.75 variant

The SARS-CoV-2 Omicron BA.2.75 variant emerged in May 2022. BA.2.75 is a BA.2 descendant but is phylogenetically distinct from BA.5, the currently predominant BA.2 descendant. Here, we show that BA.2.75 has a greater effective reproduction number and different immunogenicity profile than BA.5. We determined the sensitivity of BA.2.75 to vaccinee and convalescent sera as well as a panel of clinically available antiviral drugs and antibodies. Antiviral drugs largely retained potency, but antibody sensitivity varied depending on several key BA.2.75-specific substitutions. The BA.2.75 spike exhibited a profoundly higher affinity for its human receptor, ACE2. Additionally, the fusogenicity, growth efficiency in human alveolar epithelial cells, and intrinsic pathogenicity in hamsters of BA.2.75 were greater than those of BA.2. Our multilevel investigations suggest that BA.2.75 acquired virological properties independent of BA.5, and the potential risk of BA.2.75 to global health is greater than that of BA.5.

Neuropathologic and molecular aspects of a canine distemper epizootic in red foxes in Germany

In the last fifteen years, an epidemic of canine distemper virus (CDV) with marked neurotropism has occurred in Europe after a longer period of endemic transmission. Many wildlife species have been infected, with red foxes (Vulpes vulpes) being particularly affected. Given that this species is assumed to mediate cross-species CDV infections to domestic and wild animals, tissue samples from foxes with confirmed CDV infection in North-Western Germany were investigated to better understand the neurotropic aspects of the disease. This analysis included histopathology, virus distribution and cell tropism, phenotyping of inflammatory responses and determination of the genotype of the viruses based on the phylogeny of the hemagglutinin (H) gene. The predominant lesion type is gliosis in both gray and white matter areas associated with an accumulation of Iba1+ macrophages/microglia and upregulation of major histocompatibility complex class II molecules in the brain, while sequestration of CD3+ T and Pax5+ B cell in CDV-infected foxes is limited. Demyelination is found in few foxes, characterized by reduced myelin staining with loss of CNPase+ oligodendrocytes in the cerebellar white matter and brainstem. In addition, axonal damage, characterized by β-amyloid precursor protein expression, is found mainly in these brain regions. In situ hybridization reveals a primary infection of the cerebral and cerebellar gray matter and brain stem. Iba1+ cells and NeuN+ neurons represent the main CDV targets. Sequencing of the CDV H open reading frame from fox tissues reveals that the virus strains belongs to three different sub-lineages of the Europe-1/South America-1 genotype, suggesting independent transmission lines.

Low-Cost Cell-Surface-Mimic Analysis of Ligand Interactions of Biotinylated Immune Receptors Using Surface Plasmon Resonance

On the immune cell surface, many immune receptors are expressed and modulate the inhibitory or activating signals to control the immune responses. Recently, some of these receptors have been categorized as immune checkpoint receptors and targeted for cancer immunity or autoimmune diseases. To analyze the weak and fast binding typical for immune receptor-ligand interactions, a real-time surface plasmon resonance (SPR) technique is useful. However, it sometimes becomes difficult to optimize the immobilization conditions and appropriate controls. Considering that receptor orientation is relevant for achieving function on the cell surface, it is important to immobilize ligand proteins using specific tags at the membrane proximal end to avoid steric hindrance and structural changes in specific binding regions. Here we introduce a sensor chip, Sensor Chip CAP (Cytiva), which enables reversible and orientation-controlled immobilization of biotinylated ligands, resulting in a significant cost-effective method. We further show preparation methods of several biotinylated immune receptor proteins for SPR analysis, which are also useful for structural and other functional analyses.

[Molecular basis for the multiplication of negative-strand RNA viruses: basic research and potential applications in vaccine development]

Viruses achieve their efficient reproduction by utilizing their limited components (nucleic acids, lipids, and proteins) and host cell machineries. A detailed understanding of virus-virus and virus-host interactions will lead to the elucidation of mechanisms underlying viral pathogenesis and the development of novel medical countermeasures. We elucidated the details of several such interactions and their roles in the multiplication of negative-strand RNA viruses, measles virus, and Lassa virus. These discoveries were harnessed to develop a novel genetic approach for the generation of live-attenuated vaccine candidates with a well-defined molecular mechanism of attenuation. This article describes our findings.

Short-stalk isoforms of CADM1 and CADM2 trigger neuropathogenic measles virus-mediated membrane fusion by interacting with the viral hemagglutinin

Measles virus (MeV), an enveloped RNA virus in the family Paramyxoviridae, usually causes acute febrile illness with skin rash, but in rare cases persists in the brain, causing a progressive neurological disorder, subacute sclerosing panencephalitis (SSPE). MeV bears two envelope glycoproteins, the hemagglutinin (H) and fusion (F) proteins. The H protein possesses a head domain that initially mediates receptor binding and a stalk domain that subsequently transmits the fusion-triggering signal to the F protein. We have recently shown that cell adhesion molecule 1 (CADM1, also known as IGSF4A, Necl-2, SynCAM1) and CADM2 (also known as IGSF4D, Necl-3, SynCAM2) are host factors enabling cell-cell membrane fusion mediated by hyperfusogenic F proteins of neuropathogenic MeVs as well as MeV spread between neurons lacking the known receptors. CADM1 and CADM2 interact in cis with the H protein on the same cell membrane, triggering hyperfusogenic F protein-mediated membrane fusion. Multiple isoforms of CADM1 and CADM2 containing various lengths of their stalk regions are generated by alternative splicing. Here we show that only short-stalk isoforms of CADM1 and CADM2 predominantly expressed in the brain induce hyperfusogenic F protein-mediated membrane fusion. While the known receptors interact in trans with the H protein through its head domain, these isoforms can interact in cis even with the H protein lacking the head domain and trigger membrane fusion, presumably through its stalk domain. Thus, our results unveil a new mechanism of viral fusion triggering by host factors. Importance Measles, an acute febrile illness with skin rash, is still an important cause of childhood morbidity and mortality worldwide. Measles virus (MeV), the causative agent of measles, may also cause a progressive neurological disorder, subacute sclerosing panencephalitis (SSPE), several years after acute infection. The disease is fatal, and no effective therapy is available. Recently, we have reported that cell adhesion molecule 1 (CADM1) and CADM2 are host factors enabling MeV cell-to-cell spread in neurons. These molecules interact in cis with the MeV attachment protein on the same cell membrane, triggering the fusion protein and causing membrane fusion. CADM1 and CADM2 are known to exist in multiple splice isoforms. In this study, we report that their short-stalk isoforms can induce membrane fusion by interacting in cis with the viral attachment protein independently of its receptor-binding head domain. This finding may have important implications for cis-acting fusion triggering by host factors.

Molecular epidemiology of peste des petits ruminants virus emergence in critically endangered Mongolian saiga antelope and other wild ungulates

Peste des petits ruminants virus (PPRV) causes disease in domestic and wild ungulates, is the target of a Global Eradication Programme, and threatens biodiversity. Understanding the epidemiology and evolution of PPRV in wildlife is important but hampered by the paucity of wildlife-origin PPRV genomes. In this study, full PPRV genomes were generated from three Mongolian saiga antelope, one Siberian ibex, and one goitered gazelle from the 2016-2017 PPRV outbreak. Phylogenetic analysis showed that for Mongolian and Chinese PPRV since 2013, the wildlife and livestock-origin genomes were closely related and interspersed. There was strong phylogenetic support for a monophyletic group of PPRV from Mongolian wildlife and livestock, belonging to a clade of lineage IV PPRV from livestock and wildlife from China since 2013. Discrete diffusion analysis found strong support for PPRV spread into Mongolia from China, and phylogeographic analysis indicated Xinjiang Province as the most likely origin, although genomic surveillance for PPRV is poor and lack of sampling from other regions could bias this result. Times of most recent common ancestor (TMRCA) were June 2015 (95 per cent highest posterior density (HPD): August 2014 to March 2016) for all Mongolian PPRV genomes and May 2016 (95 per cent HPD: October 2015 to October 2016) for Mongolian wildlife-origin PPRV. This suggests that PPRV was circulating undetected in Mongolia for at least 6 months before the first reported outbreak in August 2016 and that wildlife were likely infected before livestock vaccination began in October 2016. Finally, genetic variation and positively selected sites were identified that might be related to PPRV emergence in Mongolian wildlife. This study is the first to sequence multiple PPRV genomes from a wildlife outbreak, across several host species. Additional full PPRV genomes and associated metadata from the livestock-wildlife interface are needed to enhance the power of molecular epidemiology, support PPRV eradication, and safeguard the health of the whole ungulate community.

M protein of subacute sclerosing panencephalitis virus, synergistically with the F protein, plays a crucial role in viral neuropathogenicity

Subacute sclerosing panencephalitis (SSPE) is a rare fatal neurodegenerative disease caused by a measles virus (MV) variant, SSPE virus, that accumulates mutations during long-term persistent infection of the central nervous system (CNS). Clusters of mutations identified around the matrix (M) protein in many SSPE viruses suppress productive infectious particle release and accelerate cell–cell fusion, which are features of SSPE viruses. It was reported, however, that these defects of M protein function might not be correlated directly with promotion of neurovirulence, although they might enable establishment of persistent infection. Neuropathogenicity is closely related to the character of the viral fusion (F) protein, and amino acid substitution(s) in the F protein of some SSPE viruses confers F protein hyperfusogenicity, facilitating viral propagation in the CNS through cell–cell fusion and leading to neurovirulence. The F protein of an SSPE virus Kobe-1 strain, however, displayed only moderately enhanced fusion activity and required additional mutations in the M protein for neuropathogenicity in mice. We demonstrated here the mechanism for the M protein of the Kobe-1 strain supporting the fusion activity of the F protein and cooperatively inducing neurovirulence, even though each protein, independently, has no effect on virulence. The occurrence of SSPE has been estimated recently as one in several thousand in children who acquired measles under the age of 5 years, markedly higher than reported previously. The probability of a specific mutation (or mutations) occurring in the F protein conferring hyperfusogenicity and neuropathogenicity might not be sufficient to explain the high frequency of SSPE. The induction of neurovirulence by M protein synergistically with moderately fusogenic F protein could account for the high frequency of SSPE.

Genetic Characterizations and Molecular Evolution of the Measles Virus Genotype B3's Hemagglutinin (H) Gene in the Elimination Era

Measles virus (MeV) genotype B3 is one globally significant circulating genotype. Here, we present a systematic description of long-term evolutionary characterizations of the MeV genotype B3's hemagglutinin (H) gene in the elimination era. Our results show that the B3 H gene can be divided into two main sub-genotypes, and the highest intra-genotypic diversity was observed in 2004. MeV genotype B3's H gene diverged in 1976; its overall nucleotide substitution rate is estimated to be 5.697 × 10^-4 substitutions/site/year, and is slowing down. The amino acid substitution rate of genotype B3's H gene is also decreasing, and the mean effective population size has been in a downward trend since 2000. Selection pressure analysis only recognized a few sites under positive selection, and the number of positive selection sites is getting smaller. All of these observations may reveal that genotype B3's H gene is not under strong selection pressure, and is becoming increasingly conservative. MeV H-gene or whole-genome sequencing should be routine, so as to better elucidate the molecular epidemiology of MeV in the future.

Zoonotic potential of a novel bat morbillivirus

Bats are significant reservoir hosts for many viruses with zoonotic potential1. SARS-CoV-2, Ebola virus, and Nipah virus are examples of such viruses that have caused deadly epidemics and pandemics when spilled over from bats into human and animal populations2,3. Careful surveillance of viruses in bats is critical for identifying potential zoonotic pathogens. However, metagenomic surveys in bats often do not result in full-length viral sequences that can be used to regenerate such viruses for targeted characterization4. Here, we identify and characterize a novel morbillivirus from a vespertilionid bat species (Myotis riparius) in Brazil, which we term myotis bat morbillivirus (MBaMV). There are 7 species of morbilliviruses including measles virus (MeV), canine distemper virus (CDV) and rinderpest virus (RPV)5. All morbilliviruses cause severe disease in their natural hosts6–10, and pathogenicity is largely determined by species specific expression of canonical morbillivirus receptors, CD150/SLAMF111 and NECTIN412. MBaMV used Myotis spp CD150 much better than human and dog CD150 in fusion assays. We confirmed this using live MBaMV that was rescued by reverse genetics. Surprisingly, MBaMV replicated efficiently in primary human myeloid but not lymphoid cells. Furthermore, MBaMV replicated in human epithelial cells and used human NECTIN4 almost as well as MeV. Our results demonstrate the unusual ability of MBaMV to infect and replicate in some human cells that are critical for MeV pathogenesis and transmission. This raises the specter of zoonotic transmission of a bat morbillivirus.

Canine Morbillivirus from Colombian Lineage Exhibits In Silico and In Vitro Potential to Infect Human Cells

Canine morbillivirus (CDV) is a viral agent that infects domestic dogs and a vast array of wildlife species. It belongs to the Paramyxoviridae family, genus Morbillivirus, which is shared with the Measles virus (MeV). Both viruses employ orthologous cellular receptors, SLAM in mononuclear cells and Nectin-4 in epithelial cells, to enter the cells. Although CDV and MeV hemagglutinin (H) have similar functions in viral pathogenesis and cell tropism, the potential interaction of CDV-H protein with human cellular receptors is still uncertain. Considering that CDV is classified as a multi-host pathogen, the potential risk of CDV transmission to humans has not been fully discarded. In this study, we aimed to evaluate both in silico and in vitro, whether there is a cross-species transmission potential from CDV to humans. To accomplish this, the CDV-H protein belonging to the Colombian lineage was modelled. After model validations, molecular docking and molecular dynamics simulations were carried out between Colombian CDV-H protein and canine and human cellular receptors to determine different aspects of the protein-protein interactions. Moreover, cell lines expressing orthologous cellular receptors, with both reference and wild-type CDV strains, were conducted to determine the CDV cross-species transmission potential from an in vitro model. This in silico and in vitro approach suggests the possibility that CDV interacts with ortholog human SLAM (hSLAM) and human Nectin-4 receptors to infect human cell lines, which could imply a potential cross-species transmission of CDV from dogs to humans.

Unique Tropism and Entry Mechanism of Mumps Virus

Mumps virus (MuV) is an important human pathogen that causes parotitis, orchitis, oophoritis, meningitis, encephalitis, and sensorineural hearing loss. Although mumps is a vaccine-preventable disease, sporadic outbreaks have occurred worldwide, even in highly vaccinated populations. MuV not only causes systemic infection but also has a unique tropism to glandular tissues and the central nervous system. In general, tropism can be defined by multiple factors in the viral life cycle, including its entry, interaction with host factors, and host-cell immune responses. Although the underlying mechanisms of MuV tropism remain to be fully understood, recent studies on virus-host interactions have provided insights into viral pathogenesis. This review was aimed at summarizing the entry process of MuV by focusing on the glycan receptors, particularly the recently identified receptors with a trisaccharide core motif, and their interactions with the viral attachment proteins. Here, we describe the receptor structures, their distribution in the human body, and the recently identified host factors for MuV and analyze their relationship with MuV tropism.

Application of error-prone PCR to functionally probe the morbillivirus Haemagglutinin protein

The enveloped morbilliviruses utilise conserved proteinaceous receptors to enter host cells: SLAMF1 or Nectin-4. Receptor binding is initiated by the viral attachment protein Haemagglutinin (H), with the viral Fusion protein (F) driving membrane fusion. Crystal structures of the prototypic morbillivirus measles virus H with either SLAMF1 or Nectin-4 are available and have served as the basis for improved understanding of this interaction. However, whether these interactions remain conserved throughout the morbillivirus genus requires further characterisation. Using a random mutagenesis approach, based on error-prone PCR, we targeted the putative receptor binding site for SLAMF1 interaction on peste des petits ruminants virus (PPRV) H, identifying mutations that inhibited virus-induced cell-cell fusion. These data, combined with structural modelling of the PPRV H and ovine SLAMF1 interaction, indicate this region is functionally conserved across all morbilliviruses. Error-prone PCR provides a powerful tool for functionally characterising functional domains within viral proteins.

A durable protective immune response to wild-type measles virus infection of macaques is due to viral replication and spread in lymphoid tissues

Infection with wild-type (WT) measles virus (MeV) is an important cause of childhood mortality that leads to lifelong protective immunity in survivors. WT MeV and the live-attenuated MeV used in the measles vaccine (LAMV) are antigenically similar, but the determinants of attenuation are unknown, and protective immunity induced by LAMV is less robust than that induced by WT MeV. To identify factors that contribute to these differences, we compared virologic and immunologic responses after respiratory infection of rhesus macaques with WT MeV or LAMV. In infected macaques, WT MeV replicated efficiently in B and T lymphocytes with spreading throughout lymphoid tissues resulting in prolonged persistence of viral RNA. In contrast, LAMV replicated efficiently in the respiratory tract but displayed limited spread to lymphoid tissue or peripheral blood mononuclear cells. In vitro, WT MeV and LAMV replicated similarly in macaque primary respiratory epithelial cells and human lymphocytes, but LAMV-infected lymphocytes produced little virus. Plasma concentrations of interleukin-1β (IL-1β), IL-12, interferon-γ (IFN-γ), CCL2, CCL11, CXCL9, and CXCL11 increased in macaques after WT MeV but not LAMV infection. WT MeV infection induced more protective neutralizing, hemagglutinin-specific antibodies and bone marrow plasma cells than did LAMV infection, although numbers of MeV-specific IFN-γ- and IL-4-producing T cells were comparable. Therefore, MeV attenuation may involve altered viral replication in lymphoid tissue that limited spread and decreased the host antibody response, suggesting a link between lifelong protective immunity and the ability of WT MeV, but not LAMV, to spread in lymphocytes.

Sendai Virus-Vectored Vaccines That Express Envelope Glycoproteins of Respiratory Viruses

Human respiratory syncytial virus (HRSV), human metapneumovirus (HMPV), and human parainfluenza viruses (HPIVs) are leading causes of respiratory disease in young children, the elderly, and individuals of all ages with immunosuppression. Vaccination strategies against these pneumoviruses and paramyxoviruses are vast in number, yet no licensed vaccines are available. Here, we review development of Sendai virus (SeV), a versatile pediatric vaccine that can (a) serve as a Jennerian vaccine against HPIV1, (b) serve as a recombinant vaccine against HRSV, HPIV2, HPIV3, and HMPV, (c) accommodate foreign genes for viral glycoproteins in multiple intergenic positions, (d) induce durable, mucosal, B-cell, and T-cell immune responses without enhanced immunopathology, (e) protect cotton rats, African green monkeys, and chimpanzees from infection, and (f) be formulated into a vaccine cocktail. Clinical phase I safety trials of SeV have been completed in adults and 3–6-year-old children. Clinical testing of SeVRSV, an HRSV fusion (F) glycoprotein gene recombinant, has also been completed in adults. Positive results from these studies, and collaborative efforts with the National Institutes of Health and the Serum Institute of India assist advanced development of SeV-based vaccines. Prospects are now good for vaccine successes in infants and consequent protection against serious viral disease.

Whole genomes reveal multiple candidate genes and pathways involved in the immune response of dolphins to a highly infectious virus

Wildlife species are challenged by various infectious diseases that act as important demographic drivers of populations and have become a great conservation concern particularly under growing environmental changes. The new era of whole genome sequencing provides new opportunities and avenues to explore the role of genetic variants in the plasticity of immune responses, particularly in non-model systems. Cetacean morbillivirus (CeMV) has emerged as a major viral threat to cetacean populations worldwide, contributing to the death of thousands of individuals of multiple dolphin and whale species. To understand the genomic basis of immune responses to CeMV, we generated and analysed whole genomes of 53 Indo-Pacific bottlenose dolphins (Tursiops aduncus) exposed to Australia's largest known CeMV-related mortality event that killed at least 50 dolphins from three different species. The genomic data set consisted of 10,168,981 SNPs anchored onto 23 chromosome-length scaffolds and 77 short scaffolds. Whole genome analysis indicated that levels of inbreeding in the dolphin population did not influence the outcome of an individual. Allele frequency estimates between survivors and nonsurvivors of the outbreak revealed 15,769 candidate SNPs, of which 689 were annotated to 295 protein coding genes. These included 50 genes with functions related to innate and adaptive immune responses, and cytokine signalling pathways and genes thought to be involved in immune responses to other morbilliviruses. Our study characterised genomic regions and pathways that may contribute to CeMV immune responses in dolphins. This represents a stride towards clarifying the complex interactions of the cetacean immune system and emphasises the value of whole genome data sets in understanding genetic elements that are essential for species conservation, including disease susceptibility and adaptation.

Computational Analysis Reveals a Critical Point Mutation in the N-Terminal Region of the Signaling Lymphocytic Activation Molecule Responsible for the Cross-Species Infection with Canine Distemper Virus

Infection of hosts by morbilliviruses is facilitated by the interaction between viral hemagglutinin (H-protein) and the signaling lymphocytic activation molecule (SLAM). Recently, the functional importance of the n-terminal region of human SLAM as a measles virus receptor was demonstrated. However, the functional roles of this region in the infection process by other morbilliviruses and host range determination remain unknown, partly because this region is highly flexible, which has hampered accurate structure determination of this region by X-ray crystallography. In this study, we analyzed the interaction between the H-protein from canine distemper virus (CDV-H) and SLAMs by a computational chemistry approach. Molecular dynamics simulations and fragment molecular orbital analysis demonstrated that the unique His28 in the N-terminal region of SLAM from Macaca is a key determinant that enables the formation of a stable interaction with CDV-H, providing a basis for CDV infection in Macaca. The computational chemistry approach presented should enable the determination of molecular interactions involving regions of proteins that are difficult to predict from crystal structures because of their high flexibility.

Mink SLAM V-Region V74I Substitutions Contribute to the Formation of Syncytia Induced by Canine Distemper Virus

The Signal lymphatic activation molecule (SLAM, also known as CD150) as the cellular receptor of canine distemper virus (CDV) plays an important role in the virus-host interaction. However, it is still unknown whether amino acid differences in the SLAM variable (V) region affect the formation of syncytia. Here, using raccoon dog SLAM (rSLAM) and mink SLAM (mSLAM), we performed SLAM-V homologous modeling, site-directed mutagenesis, and surface expression analysis, as well as a cell fusion assay, to study the interaction between SLAM and CDV. More specifically, our investigation focused on two amino acid residues (74 and 129) of SLAM, previously predicted to play a relevant role in receptor-ligand interaction. Our results indicated that only residues at position 60, 74, and 129 were different between rSLAM and mSLAM among the 29 amino acids that might interact with CDV H, and residues 74 and 129 were located in the interface region interacting with CDV H. The amino acid substitution at the positions of 74 have a significant effect on the expression of mSLAM. The SLAM-V74I mutation in mink significantly improved the cell fusion efficiency of CDV. In contrast, the SLAM-I74V mutation in the raccoon dog significantly decreased cell fusion efficiency. We conclude that residue 74 of SLAM plays an important role during the the formation of syncytia. Only when implementing CDV infection analysis, the rSLAM-Q129R can significantly decreased the mean number of syncytia, but the mSLAM-R129Q can't. Additionally, residue 60 show variability between rSLAM and mSLAM. We believe that our study makes a significant contribution to the literature because we provide molecular data, partially accounting for the differences in host membrane and virus interaction laying the foundation for further molecular work.

Interaction of Signaling Lymphocytic Activation Molecule Family 1 (SLAMF1) receptor with Trypanosoma cruzi is strain-dependent and affects NADPH oxidase expression and activity

The receptor Signaling Lymphocyte-Activation Molecule Family 1 (SLAMF1) controls susceptibility to Infection by the lethal Trypanosoma cruzi Y strain. To elucidate whether genetic diversity of the parasite was related with disease susceptibility, we further analyzed the role of SLAMF1 using 6 different Trypanosoma cruzi strains including Y. The interaction of SLAMF1 receptor with T. cruzi was evidenced by fluorescence microscopy, flow cytometry and quantitative PCR. All the strains, except VFRA, showed a decrease in parasite load in infected macrophages in Slamf1^-/- compared to BALB/c. In macrophages gene expression NADPH oxidase (NOX2), and reactive oxygen species (ROS) production increased in Slamf1^-/- compared to BALB/c in 5 out of 6 strains. However, Slamf1^-/-macrophages infected with VFRA strain exhibited a divergent behavior, with higher parasite load, lower NOX2 expression and ROS production compared to BALB/c. Parasitological and immunological studies in vivo with Y strain showed that in the absence of SLAMF1 the immune response protected mice from the otherwise lethal Y infection favoring a proinflammatory response likely involving CD4, CD8, dendritic cells and classically activated macrophages. In the case of VFRA, no major changes were observed in the absence of SLAMF1. Thus, the results suggest that the T. cruzi affects SLAMF1-dependent ROS production, controlling parasite replication in macrophages and affecting survival in mice in a strain-dependent manner. Further studies will focus in the identification of parasite molecules involved in SLAMF1 interaction to explain the immunopathogenesis of the disease.

Chagas disease, caused by Trypanosoma cruzi, is characterized by an acute phase, with low mortality, and after many years without any sign of disease, patients develop a symptomatic chronic phase, characterized by cardiomyopathy and/or digestive mega syndromes. These differences have been attributed to the high genetic variability of this parasite. We have shown that the receptor Signaling Lymphocyte-Activation Molecule Family 1 (SLAMF1) controls susceptibility to Infection by the lethal T. cruzi Y strain. Here we studied in detail the immunopathogenic role of SLAMF1 using 6 genetically diverse strains of T. cruzi using in vitro and in vivo approaches. Our results indicate an important role of SLAMF1 in T. cruzi infection which is parasite strain-dependent. We found that parasites interact with SLAMF1 in macrophages affecting NADPH oxidase (NOX2) expression and reactive oxygen species (ROS) production 5 out of 6 strains tested. Y and VFRA strains showed a divergent behavior in vitro and the role of SLAMF1 in the in vivo infection was also strikingly different. The Y strain caused 70% mortality in BALB/c mice but not in Slamf1^-/- mice. The proinflammatory response was stronger in the last, suggesting that SLAMF1 was repressing protective immune responses of mice infected with the Y strain. In contrast, for VFRA, SLAMF1 deficiency resulted in 100% survival of BALB/c mice, without major changes in the immune response in the absence of SLAMF1. Thus, the results indicate that SLAMF1 receptor interacts with T. cruzi, affecting parasite replication and ROS production in macrophages as well as the adaptive immune response in mice in a parasite strain-dependent manner. Future studies will focus in understanding the immunopathogenic role of SLAMF1 during T. cruzi infection.

Human parainfluenza virus fusion complex glycoproteins imaged in action on authentic viral surfaces

Infection by human parainfluenza viruses (HPIVs) causes widespread lower respiratory diseases, including croup, bronchiolitis, and pneumonia, and there are no vaccines or effective treatments for these viruses. HPIV3 is a member of the Respirovirus species of the Paramyxoviridae family. These viruses are pleomorphic, enveloped viruses with genomes composed of single-stranded negative-sense RNA. During viral entry, the first step of infection, the viral fusion complex, comprised of the receptor-binding glycoprotein hemagglutinin-neuraminidase (HN) and the fusion glycoprotein (F), mediates fusion upon receptor binding. The HPIV3 transmembrane protein HN, like the receptor-binding proteins of other related viruses that enter host cells using membrane fusion, binds to a receptor molecule on the host cell plasma membrane, which triggers the F glycoprotein to undergo major conformational rearrangements, promoting viral entry. Subsequent fusion of the viral and host membranes allows delivery of the viral genetic material into the host cell. The intermediate states in viral entry are transient and thermodynamically unstable, making it impossible to understand these transitions using standard methods, yet understanding these transition states is important for expanding our knowledge of the viral entry process. In this study, we use cryo-electron tomography (cryo-ET) to dissect the stepwise process by which the receptor-binding protein triggers F-mediated fusion, when forming a complex with receptor-bearing membranes. Using an on-grid antibody capture method that facilitates examination of fresh, biologically active strains of virus directly from supernatant fluids and a series of biological tools that permit the capture of intermediate states in the fusion process, we visualize the series of events that occur when a pristine, authentic viral particle interacts with target receptors and proceeds from the viral entry steps of receptor engagement to membrane fusion.

Measles Virus Hemagglutinin Protein Establishes a Specific Interaction With the Extreme N-Terminal Region of Human Signaling Lymphocytic Activation Molecule to Enhance Infection

Measles virus (MV) is a human pathogen that is classified in the genus Morbillivirus in the family Paramyxoviridae together with several non-human animal morbilliviruses. They cause severe systemic infections by using signaling lymphocytic activation molecule (SLAM) and poliovirus receptor-like 4 expressed on immune and epithelial cells, respectively, as receptors. The viral hemagglutinin (H) protein is responsible for the receptor-binding. Previously determined structures of MV-H and SLAM complexes revealed a major binding interface between the SLAM V domain and MV-H with four binding components (sites 1–4) in the interface. We studied the MV-H and human SLAM (hSLAM) complex structure in further detail by in silico analyses and determined missing regions or residues in the previously determined complex structures. These analyses showed that, in addition to sites 1–4, MV-H establishes a unique interaction with the extreme N-terminal region (ExNTR) of hSLAM. The first principles calculation-based fragment molecular orbital computation method revealed that methionine at position 29 (hSLAM-Met29) is the key residue for the interaction. hSLAM-Met29 was predicted to establish a CH-π interaction with phenylalanine at position 549 of MV-H (MVH-Phe549). A cell-cell fusion assay showed that the hSLAM-Met29 and MVH-Phe549 interaction is important for hSLAM-dependent MV membrane fusion. Furthermore, Jurkat cell lines expressing hSLAM with or without Met29 and recombinant MV possessing the H protein with or without Phe549 showed that the hSLAM-Met29 and MVH-Phe549 interaction enhanced hSLAM-dependent MV infection by ~10-fold. We speculate that in the evolutionary history of morbilliviruses, this interaction may have contributed to MV adaptation to humans because this interaction is unique for MV and only MV uses hSLAM efficiently among morbilliviruses.

Characterization and Comparison of SLAM/CD150 in Free-Ranging Coyotes, Raccoons, and Skunks in Illinois for Elucidation of Canine Distemper Virus Disease

Canine distemper virus (CDV) is a cause of significant disease in canids and increasingly recognized as a multi-host pathogen, particularly of non-canid families within Carnivora. CDV outbreaks in sympatric mesocarnivores are routinely diagnosed in the Forest Preserve District of Cook County, Illinois. CDV is diagnosed more commonly and the disease more severe in raccoons and striped skunks than in coyotes. Research in other species suggests host cell receptors may play a role in variable disease outcome, particularly, the signaling lymphocyte activation molecule (SLAM) located on lymphoid cells. To evaluate receptor differences, partial SLAM genes were sequenced, and predicted amino acid (AA) sequences and structural models of the proposed viral interface assessed. Of 263 aligned nucleotide base pairs, 36 differed between species with 24/36 differences between canid and non-canids. Raccoon and skunk predicted AA sequences had higher homology than coyote and raccoon/skunk sequences and 8/11 residue differences were between coyote and raccoons/skunks. Though protein structure was similar, few residue differences were associated with charge and electrostatic potential surface alterations between canids and non-canids. RNAScope^®(Advanced Cell Diagnostics, Silicon Valley, USA) ISH revealed low levels of expression that did not differ significantly between species or tissue type. Results suggest that differences in host receptors may impact species-specific disease manifestation.

Structural characteristics of measles virus entry

Measles virus, a member of the genus Morbillivirus, is highly contagious and still shows considerable mortality with over 100000 deaths annually, although efficient attenuated vaccines exist. Recent studies of measles virus haemagglutinin (MeV-H) and its receptor, including crystallographic and electron microscopic structural analyses combined with functional assays, have revealed how the MeV-H protein recognizes its cognate receptors, SLAM and Nectin-4, and how the glycan shield ensures effective vaccination. In addition, the crystal structure of the MeV-F protein indicated its similarity to those of other paramyxoviruses. Taking into account these data, several models of viral entry/membrane fusion of measles viruses and related paramyxoviruses have been proposed. Furthermore, anti-MeV-F inhibitors targeted to specific regions to inhibit MeV-F protein activation were reported, with potency for preventing MeV infection. The inhibitors targeted for entry events may potentially be applied to treatment of MeV-derived diseases, although escape mutations and drug profiles should be considered.

Large-Scale Expression and Purification of Mumps Virus Hemagglutinin-Neuraminidase for Structural Analyses and Glycan-Binding Assays

Many viruses utilize cell-surface glycans as receptors for host cell entry. Viral surface glycoproteins specifically interact with glycan motifs, which strongly contributes to viral tropism. Recently, the interactions between host cell glycan receptors and the mumps virus (MuV) hemagglutinin-neuraminidase (MuV-HN) protein were characterized by determining the co-crystal structure of MuV-HN in complex with glycan receptors. Here, we describe protocols for large-scale expression, purification and crystallization of MuV-HN proteins for structural analyses and glycan-binding assays with the overarching goal of investigating glycan-protein interactions.

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.

Expanding Diversity of Susceptible Hosts in Peste Des Petits Ruminants Virus Infection and Its Potential Mechanism Beyond

Peste des petits ruminants (PPR) is a severe respiratory and digestive tract disease of domestic small ruminants caused by PPR virus (PPRV) of the genus Morbillivirus. Although the primary hosts of PPRV are goats and sheep, the host range of PPRV has been continuously expanding and reported to infect various animal hosts over the last decades, which could bring a potential challenge to effectively control and eradicate PPR globally. In this review, we focused on current knowledge about host expansion and interspecies infection of PPRV and discussed the potential mechanisms involved.