Carbohydrate composition of the membrane glycoprotein of vesicular stomatitis virus

Vesicular stomatitis virus glycoprotein suppresses nuclear factor kappa-B- and mitogen-activated protein kinase-mediated pro-inflammatory responses dependent on sialic acids

Vesicular stomatitis (VS), characterized by vesicular lesions, produces significant economic losses in livestock industry. Infection by its causative agent, VS virus (VSV), has been previously shown to be mediated by the glycoprotein (G) during attachment, endocytosis and membrane fusion. In the current study, we revealed a novel role of VSV G protein in negative regulation of host cell pro-inflammatory responses. We determined that VSV G protein inhibited lipopolysaccharide (LPS)-induced pro-inflammatory responses as naïve VSV virions in murine peritoneal macrophage-like cell line RAW 264.7. Furthermore, we identified that VSV G protein suppressed nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPK)-mediated pro-inflammatory pathways in a dose-dependent manner. Moreover, we demonstrated that α2-3-linked sialic acids on VSV G protein were involved in antagonizing NF-κB- and MAPK-mediated pro-inflammatory responses. All these results expand the knowledge of VSV pathogenesis and strengthen the importance of VSV G protein in host innate immunity, which support implications for the development of VSV-based vaccination and oncolysis.

Addicted to sugar: roles of glycans in the order Mononegavirales

Glycosylation is a biologically important protein modification process by which a carbohydrate chain is enzymatically added to a protein at a specific amino acid residue. This process plays roles in many cellular functions, including intracellular trafficking, cell-cell signaling, protein folding and receptor binding. While glycosylation is a common host cell process, it is utilized by many pathogens as well. Protein glycosylation is widely employed by viruses for both host invasion and evasion of host immune responses. Thus better understanding of viral glycosylation functions has potential applications for improved antiviral therapeutic and vaccine development. Here, we summarize our current knowledge on the broad biological functions of glycans for the Mononegavirales, an order of enveloped negative-sense single-stranded RNA viruses of high medical importance that includes Ebola, rabies, measles and Nipah viruses. We discuss glycobiological findings by genera in alphabetical order within each of eight Mononegavirales families, namely, the bornaviruses, filoviruses, mymonaviruses, nyamiviruses, paramyxoviruses, pneumoviruses, rhabdoviruses and sunviruses.

Membrane Glycoproteins of Enveloped Viruses

This chapter focuses on the recent information of the glycoprotein components of enveloped viruses and points out specific findings on viral envelopes. Although enveloped viruses of different major groups vary in size and shape, as well as in the molecular weight of their structural polypeptides, there are general similarities in the types of polypeptide components present in virions. The types of structural components found in viral membranes are summarized briefly in the chapter. All the enveloped viruses studied to date possess one or more glycoprotein species and lipid as a major structural component. The presence of carbohydrate covalently linked to proteins is demonstrated by the incorporation of a radioactive precursor, such as glucosamine or fucose, into viral polypeptides, which is resolved by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Enveloped viruses share many common features in the organization of their structural components, as indicated by several approaches, including electron microscopy, surface-labeling, and proteolytic digestion experiments, and the isolation of subviral components. The chapter summarizes the detailed structure of the glycoproteins of four virus groups: (1) influenza virus glycoproteins, (2) rhabdovirus G protein, (3) togavirus glycoprotein, and (4) paramyxovirus glycoproteins The information obtained includes the size and shape of viral glycoproteins, the number of polypeptide chains in the complete glycoprotein structure, and compositional data on the polypeptide and oligosaccharide portions of the molecules.

Modulation of glycosylation and transport of viral membrane glycoproteins by a sodium ionophore

Analysis of viral glycoprotein expression on surfaces of monensin-treated cells using a fluorescence-activated cell sorter (FACS) demonstrated that the sodium ionophore completely inhibited the appearance of the vesicular stomatitis virus (VSV) G protein on (Madin-Darby canine kidney) MDCK cell surfaces. In contrast, the expression of the influenza virus hemagglutinin (HA) glycoprotein on the surfaces of MDCK cells was observed to occur at high levels, and the time course of its appearance was not altered by the ionophore. Viral protein synthesis was not inhibited by monensin in either VSV- or influenza virus-infected cells. However, the electrophoretic mobilities of viral glycoproteins were altered, and analysis of pronase-derived glycopeptides by gel filtration indicated that the addition of sialic acid residues to the VSV G protein was impaired in monensin-treated cells. Reduced incorporation of fucose and galactose into influenza virus HA was observed in the presence of the ionophore, but the incompletely processed HA protein was cleaved, transported to the cell surface, and incorporated into budding virus particles. In contrast to the differential effects of monensin on VSV and influenza virus replication previously observed in monolayer cultures of MDCK cells, yields of both viruses were found to be significantly reduced by high concentrations of monensin in suspension cultures, indicating that cellular architecture may play a role in determining the sensitivity of virus replication to the drug. Nigericin, an ionophore that facilitates transport of potassium ions across membranes, blocked the replication of both influenza virus and VSV in MDCK cell monolayers, indicating that the ion specificity of ionophores influences their effect on the replication of enveloped viruses.

Separation of glycopeptides by high performance liquid chromatography

A method is presented for separation of tryptic glycopeptides-containing oligosaccharides of the N-asparagine-linked type. High performance liquid chromatography (HPLC) of glycopeptides on a C18 reverse-phase system eluted with a gradient of 0%-50% acetonitrile in 0.1 M NaPO4 pH 2.2 resolves the two major glycosylation sites from the envelope glycoprotein (G) of vesicular stomatitis virus. Glycopeptides containing N-linked oligosaccharides of the complex type coelute with those containing N-linked oligosaccharides of the neutral, high mannose type, indicating that separation is based upon peptide rather than carbohydrate composition. The contribution of the carbohydrate component to glycopeptide elution, as determined by cleavage of the high mannose oligosaccharides with endo-beta-Nacetylglucosaminidase H, is that of a significant, but minor, decrease in peptide retention time. Comparison of the tryptic glycopeptide profiles of G isolated from both wild type and mutant strains of VSV illustrates the rapid, reproducible, and quantitative nature of the technique. Through HPLC analysis of appropriately treated glycopeptides, it is possible to explore both the nature and extent of glycosylation at individual sites in glycoproteins in a single step.

Electrochemical modification of vesicular stomatitis virus glycoprotein by host cell transformation

Electrochemical properties of the glycoprotein of vesicular stomatitis virus (VSV) grown in Rous sarcoma virus (RSV)-transformed cells was compared with that of its counterpart grown in nontransformed cells. In DEAE-Sephadex column chromatography, the glycoproteins of VSV derived from transformed cells appeared more heterogeneous and had a tendency to elute with higher concentrations of NaCl than those from nontransformed cells. In isoelectric focussing, the glycoproteins of VSVs derived from transformed and nontransformed cells appeared as multiple components differing in the isoelectric point, and the glycoproteins from virus from transformed cells had isoelectric points that were more acidic than their counterparts from nontransformed cells. These results show that the glycoprotein of VSV consists of populations of molecules differing in charge and their isoelectric points were shifted to the acidic side by host cell transformation.

Polarized distribution of viral envelope proteins in the plasma membrane of infected epithelial cells

The surface distribution of the envelope glycoproteins of influenza, Sendai and Vesicular Stomatitis viruses was studied by immunofluorescence and immunoelectromicroscopy in infected epithelial cell monolayers, from which these viruses bud in a polarized fashion. It was found that before the onset of viral budding, the envelope proteins are exclusively localized into the same plasma membrane domains of the epithelial cells from which the virions ultimately bud: the glycoproteins of influenza and Sendai were detected at the apical surface, while the G protein of Vesicular Stomatitis virus was concentrated at the basolateral region. On the other hand, Sendai virus nucleocapsids, which can be easily identified in the cytoplasm before viral assembly, could be observed throughout the cell, not showing any preferential localization near the surface that the virions utilize for budding. These results are consistent with a model in which the asymmetric distribution of viral envelope proteins, rather than a polarized delivery of nucleocapsids, directs the polarity of viral budding. Furthermore, the asymmetric surface localization of viral glycoproteins suggests that these proteins share with intrinsic surface proteins of epithelial cells common biogenetic mechanisms and informational features or "sorting out" signals that determine their compartmentalization in the plasma membrane.

Purification and characterization of altered cystic fibrosis liver alpha-L-fucosidase

alpha-L-Fucosidase (E.C.3.2.4.51) from two cystic fibrosis livers has been purified and characterized. Purification was accomplished by an affinity chromatographic procedure previously used for normal liver alpha-L-fucosidase. Characterization of the two cystic fibrosis alpha-L-fucosidases indicated that they were very similar to normal liver alpha-L-fucosidase with regard to pH optima profiles, Michaelis constants (Km's), subunit structure and antigenicity. However, gas liquid chromatographic analysis revealed altered carbohydrate compositions for both the cystic fibrosis alpha-L-fucosidases. The three major sugars found in normal purified liver alpha-L-fucosidase (mannose, N-acetylglucosamine and sialic acid) were reduced in the cystic fibrosis alpha-L-fucosidases, on average, to 51%, 44% and 32%, respectively, of their normal amounts.

Purification of the influenza hemagglutinin glycoprotein and characterization of its carbohydrate components

Hemagglutinin from influenza A/PR8 virus was purified after treatment of the virus with sodium deoxycholate followed by extraction with tri-n-butyl phosphate. This fully disrupted the virus while preserving hemagglutinating activity. The hemagglutinin was obtained in the form of small aggregates that could be separated from other viral components. Purified hemagglutinin was hydrolyzed to determine carbohydrate composition and digested with Pronase to analyze oligosaccharide structures. Sugars present in the hemagglutinin were galactose, mannose, fucose, and glucosamine in molar rates of about 6:11:2:5, and these comprised 16% of the hemagglutinin glycoprotein. Oligosaccharides obtained from virus included a major component of a molecular weight of 2,800, composed of glucosamine, galactose, mannose, and fucose, and a minor heterogenous component of a molecular weight of 1,500 to 2,000, containing predominantly mannose. The 2,800-molecular-weight oligosaccharide was a constituent of the hemagglutinin, and treatment of this large oligosaccharide with specific exo-glycosidases demonstrated the presence of terminal galactose and fucose and allowed the deduction of a general structure for this component.

Carbohydrate composition of purified human liver alpha-L-fucosidase

Human liver alpha-L-fucosidase was purified to apparent homogeneity and analyzed for carbohydrate content primarily by gas-liquid chromatography (glc). The enzyme is about 7% carbohydrate by weight and contains the following sugars (residues per 50, 000 molecular weight subunit): mannose (8.3), glucosamine (4.3) (presumably N-acetylated), sialic acid (1.6) and glucose (1.6). Galactose (0.8) and L-fucose (1.8) were also found but their presence may be due to artifacts of the purification procedure.

Oligosaccharides of the glycoprotein of rabies virus

The number of oligosaccharide side chains on rabies virus glycoprotein (G-protein) was investigated. Analysis of glycopeptides obtained by protease digestion of desialated G-protein revealed three discrete glycopeptides. Comparison of the protease digestion products from desialated and from untreated G-protein indicated a heterogeneity among the glycopeptides in the sialic acid content. Two major tryptic glycopeptides were isolated from desialated rabies virus G-protein and analyzed after protease digestion; one contained two oligosaccharide side chains and the other contained a single oligosaccharide side chain.

Glycosylation of VSV glycoprotein is similar in cystic fibrosis, heterozygous carrier, and normal human fibroblasts

The single envelope glycoprotein of vesicular stomatitis virus was used as a specific probe of glycosyltransferase activities in fibroblasts from two cystic fibrosis patients, an obligate heterozygous carrier and a normal individual. Gel filtration of pronase-digested glycopeptides from both purified virions and infected cell-associated VSV glycoprotein which had been labeled with[3H] glucosamine did not reveal any significant differences in the glycosylation patterns between the different cell cultures. All 4 cell lines were apparently able to synthesize the mannose- and glucosamine- containing core structure and branch chains terminating in sialic acid which are characteristic of asparagine-linked carbohydrate side chains in cellular glycoproteins. Analysis of tryptic glycopeptides by anion-exchange chromotography indicated that the same 2 major sites on the virus polypeptide were recognized and glycosylated in all 4 VSV-infected cell cultures. These studies suggest that the basic biochemical defect(s) in cystic fibrosis is not an absence or deficiency in enzymes responsible for the biosynthesis of complex carbohydrate side chains.

Purification and composition of the proteins from Sindbis virus grown in chick and BHK cells

Procedures are described for the purification of the Sindbis virus structural proteins. The amino acid and carbohydrate compositions of the purified proteins are presented for virus grown in BHK-21/13 and chicken embryo cells. Glycoprotein E1 from virus grown in BHK cells is deficient in a mannose-rich glycopeptide found on that glycoprotein when virus is grown in chicken embryo cells. The complex glactose-containing glycopeptides appear similar for virus grown in both hosts. However, when virus is grown in BHK cells, both glycoproteins are enriched in those glycopeptides containing more sialic acid. Since the two viral glycoproteins are difficult to separate cleanly during purification, it is suggested that there may be strong, but noncovalent, interactions between glycoproteins E1 and E2. It is also suggested that there may be an interaction between glycoprotein E2 and a component of the nucleocapsid.

Carbohydrate composition of the membrane glycoprotein of vesicular stomatitis virus grown in four mammalian cell lines

The carbohydrate composition of the membrane glycoprotein of vesicular stomatitis virus has been determined for virus grown in four different mammalian cell lines. The glycoprotein contains mannose, galactose, N-acetylglucosamine, and neuraminic acid as the major carbohydrate components, whereas N-acetyl-galactosamine and fucose are present in lesser amounts. The glycoprotein contains approximately 9-10% carbohydrate regardless of the host cell in which it is synthesized. Small quantitative differences are evident in the composition of the component sugars of the glycoprotein when the virus is grown in different host cells, and the glycoprotein of virus grown in a mouse fibroblast line (L cells) lacks fucose. The major oligosaccharide moieties of the virus glycoprotein from all cells are approximately the same size (3000-3400 daltons). The data presented here, in conjunction with previous data, indicate that the viral glycoprotein contains two major oligosaccharide constituents regardless of the host cell in which it is synthesized.