Amino acid change 335 E to K affects the sialic-acid-binding and neuraminidase activities of Urabe AM9 mumps virus hemagglutinin-neuraminidase glycoprotein

On the potentials of sialic acid derivatives as inhibitors for the mumps virus: A molecular dynamics and quantum chemistry investigation

Mumps virus is an infectious pathogen causing major health problems for humans such as encephalitis, orchitis, and parotitis. Therefore, designing an inhibitor for this virus is of great medical and public health importance. With this goal in mind, we investigate the affinity of different sialic acid-based compounds (ligands) against the hemagglutinin-neuraminidase (HN) protein of the mumps virus, using a combination of molecular dynamics (MD) simulations and quantum chemistry calculations. Our MD simulation results indicate that the ligands form stable complexes with the HN protein through a combination of electrostatic, van der Waals (vdW), and hydrogen bond (H-bond) interactions, which the electrostatic interactions play a more important role in the complexation process. Based on the obtained results from the structural analysis Arg381, Arg291, and Arg49 play a key role in the binding site interactions with the different ligands, in comparison with other residues. There are some candidates such as Neu5Acα2-6Galβ1-4GlcNAcβ, Neu5Acα2-3Galβ1-3GlcNacβ1-3Galβ1-4Glc, and Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4Glc that form more stable complexes with the HN than the α2-3-Sialyllactose confirmed by the calculated Gibbs binding energies (-39.65, -46.93, and -36.49 kcal.mol^-1, respectively). To investigate the relationship between the molecular properties of the selected compounds and their affinity to the HN receptor, density functional theory dispersion corrected (DFT-D3) calculations were employed. According to our DFT-D3 results, neutral sialic acid-based compounds have lower reactivity to the mumps virus than the negativity charge structures. Moreover, by increasing the electronic chemical potential (μ) the vdW and H-bond interactions between drugs and the HN protein increase. In other words, by elevating the electron tendency of the selected ligands their affinity to the mumps virus increases. Our quantum chemistry calculations reveal that in addition to the structural features the molecular properties of the drugs can play important roles in their affinity and reactivity against the virus. The results of this study can provide useful details to design new compounds or improve their properties against the mumps virus.

Exploring the Mumps Virus Glycoproteins: A Review

The resurgence of mumps in vaccinated adult populations has raised concerns about possible waning vaccine immunity or a potential lack of protection to the circulating strain. A number of individual studies have investigated if there are amino acid variations between the circulating wild-type strains and vaccine strains. In these studies, the HN and F mumps surface glycoproteins have been of interest, because of their role in viral infection, and because the HN protein is the target of neutralizing antibodies. Here, we summarize the single nucleotide variants and their potential effect that have been identified between mumps genotypes in the HN and F proteins.

Differential Features of Fusion Activation within the Paramyxoviridae

Paramyxovirus (PMV) entry requires the coordinated action of two envelope glycoproteins, the receptor binding protein (RBP) and fusion protein (F). The sequence of events that occurs during the PMV entry process is tightly regulated. This regulation ensures entry will only initiate when the virion is in the vicinity of a target cell membrane. Here, we review recent structural and mechanistic studies to delineate the entry features that are shared and distinct amongst the Paramyxoviridae. In general, we observe overarching distinctions between the protein-using RBPs and the sialic acid- (SA-) using RBPs, including how their stalk domains differentially trigger F. Moreover, through sequence comparisons, we identify greater structural and functional conservation amongst the PMV fusion proteins, as compared to the RBPs. When examining the relative contributions to sequence conservation of the globular head versus stalk domains of the RBP, we observe that, for the protein-using PMVs, the stalk domains exhibit higher conservation and find the opposite trend is true for SA-using PMVs. A better understanding of conserved and distinct features that govern the entry of protein-using versus SA-using PMVs will inform the rational design of broader spectrum therapeutics that impede this process.

The Sialic Acid Binding Activity of Human Parainfluenza Virus 3 and Mumps Virus Glycoproteins Enhances the Adherence of Group B Streptococci to HEp-2 Cells

In the complex microenvironment of the human respiratory tract, different kinds of microorganisms may synergistically interact with each other resulting in viral-bacterial co-infections that are often associated with more severe diseases than the respective mono-infections. Human respiratory paramyxoviruses, for example parainfluenza virus type 3 (HPIV3), are common causes of respiratory diseases both in infants and a subset of adults. HPIV3 recognizes sialic acid (SA)-containing receptors on host cells. In contrast to human influenza viruses which have a preference for α2,6-linked sialic acid, HPIV3 preferentially recognize α2,3-linked sialic acids. Group B streptococci (GBS) are colonizers in the human respiratory tract. They contain a capsular polysaccharide with terminal sialic acid residues in an α2,3-linkage. In the present study, we report that HPIV3 can recognize the α2,3-linked sialic acids present on GBS. The interaction was evident not only by the binding of virions to GBS in a co-sedimentation assay, but also in the GBS binding to HPIV3-infected cells. While co-infection by GBS and HPIV3 had a delaying effect on the virus replication, it enhanced GBS adherence to virus-infected cells. To show that other human paramyxoviruses are also able to recognize the capsular sialic acid of GBS we demonstrate that GBS attaches in a sialic acid-dependent way to transfected BHK cells expressing the HN protein of mumps virus (MuV) on their surface. Overall, our results reveal a new type of synergism in the co-infection by respiratory pathogens, which is based on the recognition of α2,3-linked sialic acids. This interaction between human paramyxoviruses and GBS enhances the bacterial adherence to airway cells and thus may result in more severe disease.

Neuraminidase activity of blue eye disease porcine rubulavirus: Specificity, affinity and inhibition studies

Porcine rubulavirus (PorPV), also known as La Piedad Michoacan Virus (LPMV) causes encephalitis and reproductive failure in newborn and adult pigs, respectively. The hemagglutinin-neuraminidase (HN) glycoprotein is the most exposed and antigenic of the virus proteins. HN plays central roles in PorPV infection; i.e., it recognizes sialic acid-containing cell receptors that mediate virus attachment and penetration; in addition, its neuraminidase (sialic acid releasing) activity has been proposed as a virulence factor. This work describes the purification and characterization of PorPV HN protein (isolate PAC1). The specificity of neuraminidase is restricted to sialyl(α2,3)lactose (3SL). HN showed typical Michaelis-Menten kinetics with fetuin as substrate (km=0.029μM, Vmax=522.8nmolmin^-1mg^-1). When 3SL was used as substrate, typical cooperative kinetics were found (S₅₀=0.15μM, Vmax=154.3nmolmin^-1mg^-1). The influenza inhibitor zanamivir inhibited the PorPV neuraminidase with IC₅₀ of 0.24μM. PorPV neuraminidase was activated by Ca²⁺ and inhibited by nucleoside triphosphates with the level of inhibition depending on phosphorylation level. The present results open possibilities to study the role of neuraminidase in the pathogenicity of PorPV infection and its potential inhibitors.

Zoonotic Potential of Emerging Paramyxoviruses: Knowns and Unknowns

The risk of spillover of enzootic paramyxoviruses and the susceptibility of recipient human and domestic animal populations are defined by a broad collection of ecological and molecular factors that interact in ways that are not yet fully understood. Nipah and Hendra viruses were the first highly lethal zoonotic paramyxoviruses discovered in modern times, but other paramyxoviruses from multiple genera are present in bats and other reservoirs that have unknown potential to spillover into humans. We outline our current understanding of paramyxovirus reservoir hosts and the ecological factors that may drive spillover, and we explore the molecular barriers to spillover that emergent paramyxoviruses may encounter. By outlining what is known about enzootic paramyxovirus receptor usage, mechanisms of innate immune evasion, and other host-specific interactions, we highlight the breadth of unexplored avenues that may be important in understanding paramyxovirus emergence.

Genetic variation in the HN and SH genes of mumps viruses: a comparison of strains from mumps cases with and without neurological symptoms

BACKGROUND

It is known that mumps virus (MuV) strains may vary in their neurovirulent capacity, and certain MuV strains may be highly neurotropic. In animal models and epidemiological studies, mutations at specific amino acids (aa) have been proposed to be associated with neurovirulence. To assess whether these genetic variations can be observed in clinical samples from patients and if they correlate with neurovirulence as determined by clinical symptoms, 39 mumps patients with or without neurological symptoms were investigated.

PRINCIPAL FINDINGS

Respiratory samples, oral fluids, throat swabs, and neurological and cerebrospinal fluid samples were tested by RT-PCR and products sequenced. Sequences of the entire small hydrophobic (SH) gene and the partial hemagglutinin-neuraminidase (HN) gene were compared.

CONCLUSIONS

The results showed there was no significant difference between the samples of the two groups of patients at the aa sites in either the HN protein or the SH protein, which have previously been hypothesized to be associated with neurovirulence or antigenicity. The occurrence of neurological symptoms of mumps does not appear to be due to a single point mutation in either the HN or SH gene.

The use of sialidase therapy for respiratory viral infections

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DAS181 is a novel inhaled therapy for the treatment of influenza.

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Treatment targets sialic acid on the cell surface.

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The sialidase removes both α2-3 and α2-6 linked sialic acids.

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The use of an amphiregulin tag to the sialidase anchors it to the cell surface.

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Treatment for 3 days appears effective in treating influenza and parainfluenza.

DAS181 is an inhaled bacterial sialidase which functions by removing sialic acid (Sia) from the surface of epithelial cells, preventing attachment and subsequent infection by respiratory viruses that utilize Sia as a receptor. DAS181 is typical of bacterial sialidases in cleaving Sia α2-3 and Sia α2-6 linkages, and it also has a demonstrated effect against acetylated and hydroxylated forms of Sia. The potency of the compound has been enhanced by coupling the active sialidase with an amphiregulin tag, allowing a longer duration of action and minimizing spread to the systemic circulation. DAS181 is now in Phase II development for the treatment of influenza, and it has also demonstrated activity in individual cases of parainfluenza in immunosuppressed patients. Continued evaluation of the roles and activities of bacterial sialidases is required to expand the range of successful antiviral therapies targeting Sia or its derivatives.

Interaction of mumps virus V protein variants with STAT1-STAT2 heterodimer: experimental and theoretical studies

Background

Mumps virus V protein has the ability to inhibit the interferon-mediated antiviral response by inducing degradation of STAT proteins. Two virus variants purified from Urabe AM9 mumps virus vaccine differ in their replication and transcription efficiency in cells primed with interferon. Virus susceptibility to IFN was associated with insertion of a non-coded glycine at position 156 in the V protein (VGly) of one virus variant, whereas resistance to IFN was associated with preservation of wild-type phenotype in the V protein (VWT) of the other variant.

Results

VWT and VGly variants of mumps virus were cloned and sequenced from Urabe AM9 vaccine strain. VGly differs from VWT protein because it possesses an amino acid change Gln₁₀₃Pro (Pro¹⁰³) and the Gly¹⁵⁶ insertion. The effect of V protein variants on components of the interferon-stimulated gene factor 3 (ISGF3), STAT1 and STAT2 proteins were experimentally tested in cervical carcinoma cell lines. Expression of VWT protein decreased STAT1 phosphorylation, whereas VGly had no inhibitory effect on either STAT1 or STAT2 phosphorylation. For theoretical analysis of the interaction between V proteins and STAT proteins, 3D structural models of VWT and VGly were predicted by comparing with simian virus 5 (SV5) V protein structure in complex with STAT1-STAT2 heterodimer. In silico analysis showed that VWT-STAT1-STAT2 complex occurs through the V protein Trp-motif (W¹⁷⁴, W¹⁷⁸, W¹⁸⁹) and Glu⁹⁵ residue close to the Arg⁴⁰⁹ and Lys⁴¹⁵ of the nuclear localization signal (NLS) of STAT2, leaving exposed STAT1 Lys residues (K⁸⁵, K⁸⁷, K²⁹⁶, K⁴¹³, K⁵²⁵, K⁶⁷⁹, K⁶⁸⁵), which are susceptible to proteasome degradation. In contrast, the interaction between VGly and STAT1-STAT2 heterodimer occurs in a region far from the NLS of STAT2 without blocking of Lys residues in both STAT1 and STAT2.

Conclusions

Our results suggest that VWT protein of Urabe AM9 strain of mumps virus may be more efficient than VGly to inactivate both the IFN signaling pathway and antiviral response due to differences in their finest molecular interaction with STAT proteins.

Identification of genetic mutations associated with attenuation and changes in tropism of Urabe mumps virus

Although several effective mumps virus vaccines have been developed, almost nothing is known about the genetic changes responsible for loss of virulence. One vaccine, Urabe AM9, was withdrawn from the market because of insufficient attenuation. The vaccine was found to contain a mixture of viruses that could be distinguished based on the sequence of the hemagglutinin-neuraminidase gene (HN). Viruses containing lysine at HN amino acid position 335 were isolated from cases of post-vaccination parotitis or meningitis whereas viruses containing glutamic acid at this position were not associated with post-vaccination disease. Using a rat based model of mumps neurovirulence, we demonstrate that this latter virus is significantly attenuated compared to a virus isolated from a patient with post-vaccination meningitis. Complete sequence analysis of the genomes of the two viruses identified sixteen genetic differences, some or all of which must be responsible for differences in virulence. These same genetic differences also account for changes in tropism in cell culture.

Molecular characterization of the hemagglutinin-neuraminidase gene of porcine rubulavirus isolates associated with neurological disorders in fattening and adult pigs

"Blue eye disease" is a viral infection of swine endemic in Mexico, which produces fatal encephalitis accompanied by respiratory signs and corneal opacity in suckling piglets. An atypical blue eye disease outbreak presented high rates of neurological signs in fattening and adult pigs from 2000 to 2003. In order to identify the basis of increased neurovirulence, the hemagglutinin-neuraminidase (HN) gene of several porcine rubulavirus isolates were sequenced and compared with that of La Piedad Michoacan virus and other isolates that did not produce neurological disorders in weaned pigs. Nine amino acid mutations distinguished the high neurovirulent PAC6-PAC9 viruses, whereas five mutations characterized the low neurovirulent PAC2 and PAC3 viruses. HN protein three-dimensional models showed that the main conformation and functional domains were preserved, although substitutions A223T and A291D occurred in PAC2 and PAC3 viruses, as well as A511K and E514K presented in PAC6-PAC9 viruses considerably modified the properties of the HN protein surface. The increased positive charge of the HN protein of PAC6-PAC9 viruses seems to be associated with their increased neurovirulence.

Differential sensitivity to interferon influences the replication and transcription of Urabe AM9 mumps virus variants in nerve cells

Urabe AM9 mumps virus vaccine causes post-vaccination meningitis. Two variants of Urabe AM9 virus differ in their replication efficiency in human nerve cells, HN-A(1081) variant being more neurotropic than HN-G(1081). The effect of interferon (IFN) on viral replication and transcription was analyzed. Priming of nerve cells with IFN reduced more significantly the replication of HN-G(1081) variant (from 10(2.5) to 10(1.3) TCID(50)) than that of HN-A(1081) (from 10(3.5) to 10(2.6) TCID(50)). IFN-priming also reduced the transcription of HN-G(1081) genes, but not of HN-A(1081). The effect of viral infection on the transcription of cellular IFN responsive genes was analyzed. HN-A(1081) virus reduced the transcription of STAT1, STAT2, p48 and MxA in both unprimed and IFN-primed cells; whereas HN-G(1081) virus just reduced MxA transcription. Since rubulavirus V protein inhibits IFN signaling, the V mRNA was cloned and sequenced, finding that HN-G(1081) but not HN-A(1081) presented three extra G in the P/V edition site, producing the insertion of Gly156 in the V protein. Our results suggest that the replication efficiency of Urabe AM9 mumps virus variants is influenced by their sensitivity to interferon and their capacity to reduce the antiviral response.