Isolation of a low molecular weight sialidase (neuraminidase) from influenza virus

Microbial Neuraminidase Induces a Moderate and Transient Myelin Vacuolation Independent of Complement System Activation

AIMS

Some central nervous system pathogens express neuraminidase (NA) on their surfaces. In the rat brain, a single intracerebroventricular (ICV) injection of NA induces myelin vacuolation in axonal tracts. Here, we explore the nature, the time course, and the role of the complement system in this damage.

METHODS

The spatiotemporal analysis of myelin vacuolation was performed by optical and electron microscopy. Myelin basic protein-positive area and oligodendrocyte transcription factor (Olig2)-positive cells were quantified in the damaged bundles. Neuronal death in the affected axonal tracts was assessed by Fluoro-Jade B and anti-caspase-3 staining. To evaluate the role of the complement, membrane attack complex (MAC) deposition on damaged bundles was analyzed using anti-C5b9. Rats ICV injected with the anaphylatoxin C5a were studied for myelin damage. In addition, NA-induced vacuolation was studied in rats with different degrees of complement inhibition: normal rats treated with anti-C5-blocking antibody and C6-deficient rats.

RESULTS

The stria medullaris, the optic chiasm, and the fimbria were the most consistently damaged axonal tracts. Vacuolation peaked 7 days after NA injection and reverted by day 15. Olig2+ cell number in the damaged tracts was unaltered, and neurodegeneration associated with myelin alterations was not detected. MAC was absent on damaged axonal tracts, as revealed by C5b9 immunostaining. Rats ICV injected with the anaphylatoxin C5a displayed no myelin injury. When the complement system was experimentally or constitutively inhibited, NA-induced myelin vacuolation was similar to that observed in normal rats.

CONCLUSION

Microbial NA induces a moderate and transient myelin vacuolation that is not caused either by neuroinflammation or complement system activation.

Antiviral adhesion molecular mechanisms for influenza: W. G. Laver's lifetime obsession

Infection by the influenza virus depends firstly on cell adhesion via the sialic-acid-binding viral surface protein, haemagglutinin, and secondly on the successful escape of progeny viruses from the host cell to enable the virus to spread to other cells. To achieve the latter, influenza uses another glycoprotein, the enzyme neuraminidase (NA), to cleave the sialic acid receptors from the surface of the original host cell. This paper traces the development of anti-influenza drugs, from the initial suggestion by MacFarlane Burnet in 1948 that an effective 'competitive poison' of the virus' NA might be useful in controlling infection by the virus, through to the determination of the structure of NA by X-ray crystallography and the realization of Burnet's idea with the design of NA inhibitors. A focus is the contribution of the late William Graeme Laver, FRS, to this research.

In the shadow of hemagglutinin: a growing interest in influenza viral neuraminidase and its role as a vaccine antigen

Despite the availability of vaccine prophylaxis and antiviral therapeutics, the influenza virus continues to have a significant, annual impact on the morbidity and mortality of human beings, highlighting the continued need for research in the field. Current vaccine strategies predominantly focus on raising a humoral response against hemagglutinin (HA)—the more abundant, immunodominant glycoprotein on the surface of the influenza virus. In fact, anti-HA antibodies are often neutralizing, and are used routinely to assess vaccine immunogenicity. Neuraminidase (NA), the other major glycoprotein on the surface of the influenza virus, has historically served as the target for antiviral drug therapy and is much less studied in the context of humoral immunity. Yet, the quest to discern the exact importance of NA-based protection is decades old. Also, while antibodies against the NA glycoprotein fail to prevent infection of the influenza virus, anti-NA immunity has been shown to lessen the severity of disease, decrease viral lung titers in animal models, and reduce viral shedding. Growing evidence is intimating the possible gains of including the NA antigen in vaccine design, such as expanded strain coverage and increased overall immunogenicity of the vaccine. After giving a tour of general influenza virology, this review aims to discuss the influenza A virus neuraminidase while focusing on both the historical and present literature on the use of NA as a possible vaccine antigen.

Two birds with one stone? Possible dual-targeting H1N1 inhibitors from traditional Chinese medicine

The H1N1 influenza pandemic of 2009 has claimed over 18,000 lives. During this pandemic, development of drug resistance further complicated efforts to control and treat the widespread illness. This research utilizes traditional Chinese medicine Database@Taiwan (TCM Database@Taiwan) to screen for compounds that simultaneously target H1 and N1 to overcome current difficulties with virus mutations. The top three candidates were de novo derivatives of xylopine and rosmaricine. Bioactivity of the de novo derivatives against N1 were validated by multiple machine learning prediction models. Ability of the de novo compounds to maintain CoMFA/CoMSIA contour and form key interactions implied bioactivity within H1 as well. Addition of a pyridinium fragment was critical to form stable interactions in H1 and N1 as supported by molecular dynamics (MD) simulation. Results from MD, hydrophobic interactions, and torsion angles are consistent and support the findings of docking. Multiple anchors and lack of binding to residues prone to mutation suggest that the TCM de novo derivatives may be resistant to drug resistance and are advantageous over conventional H1N1 treatments such as oseltamivir. These results suggest that the TCM de novo derivatives may be suitable candidates of dual-targeting drugs for influenza.

Antiviral drugs for influenza: Tamiflu® past, present and future

Two antiviral drugs that are currently available for the treatment of influenza are effective against all strains of the virus, if used correctly. These are the neuraminidase inhibitors, zanamivir (Relenza®) and oseltamivir (Tamiflu®). These drugs are the result of basic research performed over a 60-year period by many people around the world. They were deliberately synthesized from a knowledge of the x-ray crystal structure of influenza virus neuraminidase. This article provides a brief historical account of some of the scientific events that lead to their creation.

Pandemic influenza: its origin and control

A "new" influenza virus will appear at some time in the future. This virus will arise by natural processes, which we do not fully understand, or it might be created by some bioterrorist. The world's population will have no immunity to the new virus, which will spread like wild-fire, causing much misery, economic disruption and many deaths. Vaccines will take time to develop and the only means of control, at least in the early stages of the epidemic, are anti-viral drugs, of which the neuraminidase inhibitors currently seem the most effective.

Characterization of influenza virus neuraminidase with hemagglutinin activity and its comparison with that of viral neuraminidase

The neuraminidase associated with the bifunctional protein, hemagglutinin-neuraminidase, of influenza virus has been characterized. The enzyme has a pH optimum of 4.5, does not require Ca2+ and is inactivated (98%) by incubation at 50 degrees C. The enzyme has a Km of 2.00 X 10(-3) M and 0.06 X 10(-3) M with the substrates 2-(3-methoxyphenyl)-N-acetylneuraminic acid and fetuin, respectively. The Ki is 400 X 10(-6) with the inhibitor 2-deoxy-2,3-dehydro-N-acetylneuraminic acid. The incorporation of labeled cysteine, valine and leucine in the hemagglutinin-neuraminidase protein is different from that of viral neuraminidase. A comparison of the properties of the neuraminidase associated with protein hemagglutinin-neuraminidase with that of viral neuraminidase or sialidase showed that the former is biochemically different and an antigenically distinct enzyme. The unique feature of the new enzyme is that it has the hemagglutinin activity as well. The two biological activities could not be separated from each other in all systems used. Apparently, protein hemagglutinin-neuraminidase is genetically transferable and it is detectable in a laboratory recombinant virus E-2971 (H3 Aichi X N7). These results suggest that protein hemagglutinin-neuraminidase is a unique surface protein of the influenza virus A/Aichi/2/68 (H3N2).

In vitro enhancement of human natural cell-mediated cytotoxicity by purified influenza virus glycoproteins

The role of the glycoproteins of influenza virus, hemagglutinin (HA), and neuraminidase (NA) in the in vitro stimulation of natural cell-mediated cytotoxicity (NCMC) or natural killer activity of human peripheral blood lymphocytes was evaluated with radiolabeled K562 cells as target cells in an overnight chromium release assay. Three different approaches were used. (i) Purified viral proteins were obtained by extraction with Nonidet P-40, separation on a sucrose gradient, and further purification by affinity chromatography. Ficoll-Hypaque-purified peripheral blood lymphocytes exposed to HA or NA individually or to a mixture of both significantly increased NCMC (32 to 50%). (ii) Treatment of HA and NA with their respective homologous antisera or F(ab')2 antibody abrogated the stimulation of NCMC by these glycoproteins. (iii) Virions treated with proteolytic enzymes resulted in viral cores lacking either HA or NA or both activities. Compared to whole virions, viral cores devoid of HA activity only induced a 50% increase in NCMC, whereas viral cores lacking HA activity and with traces of NA activity stimulated only 10% of the NCMC. These results suggest that influenza virus-induced cell-mediated cytotoxicity is largely due to its glycoproteins.

Evidence for the contribution of the host species to the extent of antigenic variation of N1 influenza virus neuraminidase

N1 influenza virus neuraminidases (NA) derived from avian, swine and human virus isolates, including the genetically related classic strains A/FPV/Rostock/34, A/Swine/1976/31, A/PR8/34 and A/FM1/47, were analysed serologically by neuraminidase inhibition (NI), inhibition of virus release (IVR) and competitive radio-immunoassays (competitive RIA). Comparing the three tests, competitive RIA appeared to be more reliable than NI and IVR for a quantitative assessment of antigenic relatedness. Together with evidence presented by others, these studies indicate that the host species contributes to the extent of antigenic variation of NAses. In contrast to NAses of human viruses where antigenic drift occurs readily, NAses of animal influenza viruses, from birds or mammalians, undergo far fewer antigen changes.

Simple and rapid separation of ortho- and paramyxovirus glycoproteins

The hemagglutinin (HA) and neuraminidase (NA) of influenza viruses, as well as the fusion protein (F) and hemagglutinin-neuraminidase (HN) of paramyxoviruses, have been separated in native form using a two-step procedure. The glycoproteins are efficiently extracted from virions using the on-ionic detergent octyl-beta-D-glucoside and are then applied to a column of agarose beads coupled with tyrosine-sulfanilic acid. Pure HA and F are obtained in good yield in the flow-through from this column. NA and HN bind strongly and can be eluted, albeit somewhat contaminated with HA or F, by raising the pH of the column buffer. The separated non-denatured fractions can be used for structural, functional, and antigenic studies.

Preparation-conditioned changes of the antigenicity of influenza virus neuraminidases

The influenza virus strains A/Sing/1/57 (H2N2), A/Bel/42 (H0N1) and A/Bel/42 (HO)-A/Sing/1/57 (N2) were treated with bromelain under reducing conditions and with reducing agent alone, and the antigenicity of the neuraminidase (NA) of intact virus and of the split products was tested comparatively. It was found that the antigenicity of NA was influenced quantitatively and qualitatively by the preparation procedure. Antineuraminidase (AN) antibodies obtained after vaccination of guinea pigs with intact virus and with split products differed in their cross-reactivity with heterologous neuraminidases. In several cases, the quantity of AN antibody formation depended on the hemagglutinin (HA) dose present in the vaccines. The N2 NA on the recombinant virus was significantly more sensitive to treatment with reducing agent than was the N2 NA on the parent virus. AN antibodies directed against N2 NA on the recombinant differed qualitatively from that directed against N2 NA of parent virus. The results warrant the conclusion that the antigenicity of isolated NA or of NA on recombinant virus can differ from that of the NA on intact homologous virus and that such alterations could influence the determination of antigenic relationship between neuraminidases.

The chemical reactions of the haemagglutinins and neuraminidases of different strains of influenza viruses. 3. Effects of proteolytic enzymes

The action of trypsin and pronase on the haemagglutinins and neuraminidases of eight strains of influenza virus has been examined.The haemagglutinins of all the strains were highly susceptible to digestion by pronase but there were great variations in resistance to trypsin.The neuraminidases of the eight strains were of three types. The neuraminidases of the A 1 strains and the DSP strain of virus A were highly susceptible to destruction by both enzymes. The neuraminidases of the PR 8 and Swine strains showed partial resistance especially to trypsin, while the A 2 strains and the LEE strains of virus B possessed neuraminidases that were completely resistant to both trypsin and pronase.Proteolytic enzymes released free neuraminidases from the A 2 and LEE viruses the morphology of which was different from that of neuraminidases released by detergent treatment.

Functional significance of sialidase during influenza virus multiplication: an electron microscope study

Morphological evidence has been obtained by electron microscopy in support of previous findings that one of the most important functions of sialidase is associated with the release of virus from infected host cells. Highly specific antiserum against fowl plague virus enzyme and specific antiserum against X7 recombinant influenza virus enzyme were shown to influence the morphology of cells infected with their homologous virus. In the presence of enzyme antiserum, an accumulation and aggregation of virus particles were evident on the cell surface and in the extracellular space of infected host cells. The aggregation of virus particles was interpreted to result from the inhibition of the release of virus.

The chemical reactions of the haemagglutinins and neuraminidases of different strains of influenza viruses. II. Effects of reagents modifying the higher order structure of the protein molecule

The results of treatment of influenza virus strains with chemical reagents acting on the higher-order structure of protein molecules shows that both the haemagglutinating and enzymic activities are susceptible to these agents but there are considerable differences between the different strains and the neuraminidase activity is more sensitive than the haemagglutinating activity.

The neuraminidase activity of A and A1strains is destroyed by urea, guanidine, urea+dithiothreitol and mercuric chloride. The haemagglutinin of the PR 8 and SWINE strains is resistant to urea and mercuric chloride but destroyed by guanidine and by urea+dithiothreitol. The haemagglutinin of the DSP strain of virus A and the A1strains is resistant to urea, guanidine and mercuric chloride but is destroyed by urea+dithiothreitol.

The neuraminidase activity of the A2strains is more resistant than that of the A and A1strains. It is resistant to mercuric chloride and partially resistant to urea but is destroyed by guanidine and by urea+dithiothreitol. The A2haemagglutinin is resistant to urea, urea+dithiothreitol, and mercuric chloride but is destroyed by guanidine.

The LEE virus neuraminidase is resistant to urea and partially resistant to guanidine but is destroyed by urea+dithiothreitol and mercuric chloride. The LEE haemagglutinin is resistant to urea, guanidine and mercuric chloride but is destroyed by urea+dithiothreitol.

It is suggested that the surface projections of the virus particle are protein polymers each made up of three or four monomers which are the components of the V antigen complex. Antigenic activity is a function of the primary or secondary structure of the monomers, haemagglutinin activity is a function of the tertiary structure of the monomers, while neuraminidase activity is a function of the quaternary structure of the polymer.

From studies of the chemical reactions of their haemagglutinins and neuraminidases strains of influenza virus A can be classified into groups. These groups are very similar to but not precisely identical with groupings made by serological methods.

Envelope protein of influenza virus. I. Hemagglutinating activity of reassociated subunits

The hemagglutinating properties of influenza virus envelope protein, prepared by reassociation of polypeptide subunits, have been defined and compared with those of virus and ether-split hemagglutinin. In general, the characteristics of the intact and ether-split virus were found to be similar, whereas those of the envelope protein were distinctly different. The use of chicken, pigeon, and guinea pig erythrocytes both at 23 and 4 C disclosed that the hemagglutinating titers of envelope protein preparations were particularly dependent on the system employed. Under optimal conditions, with guinea pig cells at 4 C, the titers of envelope protein preparations were equivalent to those of the original virus concentrates. The hemagglutinating activity of envelope protein was particularly sensitive to elevated temperature, concentrated urea, sulfhydryl-reducing reagents, and tryptic digestion at high salt concentrations. In all these respects, the intact virus was more resistant than the envelope protein. Interpretation of the data indicates that the hemagglutinin is stabilized when associated with the lipid micelle at the surface of the virus.