biology

Viral neuraminidase

Viral neuraminidase is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Viral neuraminidase rather than just read about it. In short: Viral neuraminidase is a type of neuraminidase found on the surface of influenza viruses that enables the virus to be released from the host cell. Neuraminidases are enzymes that cleave sialic acid residues from glycoproteins.

Key takeaways

Viral neuraminidase belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Viral neuraminidase to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Viral neuraminidase from memory before moving on to harder problems.

Reference excerpt

Viral neuraminidase is a type of neuraminidase found on the surface of influenza viruses that enables the virus to be released from the host cell. Neuraminidases are enzymes that cleave sialic acid residues from glycoproteins. Viral neuraminidase was discovered by Alfred Gottschalk at the Walter and Eliza Hall Institute in 1957. Neuraminidase inhibitors are antiviral agents that inhibit influenza viral neuraminidase activity and are of major importance in the control of influenza. Viral neuraminidases are the members of the glycoside hydrolase family 34 CAZY GH_34 which comprises enzymes with only one known activity; sialidase or neuraminidase EC 3.2.1.18. Neuraminidases cleave the terminal sialic acid residues from carbohydrate chains in glycoproteins. Sialic acid is a negatively charged sugar associated with the protein and lipid portions of lipoproteins. To infect a host cell, the influenza virus attaches to the exterior cell surface using hemagglutinin, a molecule found on the surface of the virus that binds to sialic acid groups. Sialic acids are found on various glycoproteins at the host cell surface. The virus then moves from sialic acid group to sialic acid group until it finds the proper cell surface receptor (whose identity remains unknown). Neuraminadase enables this movement by cleaving sialic acid groups that hemagglutinin was attached to. After the virus has entered the cell and has replicated, new viral particles bud from the host cell membrane. The hemagglutinin on new viral particles remains attached to sialic acid groups of glycoproteins on the external cell surface and the surface of other viral particles; neuraminidase cleaves these groups and thereby allows the release of viral particles and prevents self-aggregation. Neuraminadase also facilitates the movement of virus particles in the presence of mucus rich in sialic acid. A single hemagglutinin-neuraminidase protein can combine neuraminidase and hemagglutinin functions, such as in mumps virus and human parainfluenza virus.

Function The enzyme helps viruses to be released after budding from the plasma membrane of a host cell. Influenza virus membranes contain two glycoproteins: hemagglutinin and neuraminidase. While the hemagglutinin on the surface of the virion is needed for infection, its presence inhibits release of the particle after budding. Viral neuraminidase cleaves terminal sialic acid residues from glycan structures on the surface of the infected cell. This promotes the release of progeny viruses and the spread of the virus from the host cell to uninfected surrounding cells. Neuraminidase also cleaves sialic acid residues from viral proteins, preventing aggregation of viruses.

Inhibitors

Neuraminidase has been targeted in structure-based enzyme inhibitor design programmes that have resulted in the production of two drugs, zanamivir (Relenza) and oseltamivir (Tamiflu). Administration of neuraminidase inhibitors is a treatment that limits the severity and spread of viral infections. Neuraminidase inhibitors are useful for combating influenza infection: zanamivir, administered by inhalation; oseltamivir, administered orally; and under research is peramivir administered parenterally, that is through intravenous or intramuscular injection.

Neuraminidase inhibition resistance On February 27, 2005, a 14-year-old Vietnamese girl was documented to be carrying an H5N1 influenza virus strain that was resistant to the drug oseltamivir. The drug is used to treat patients that have contracted influenza. However, the Vietnamese girl who had received a prophylactic dose (75 mg once a day) was found to be non-responsive to the medication. In growing fears of a global avian flu pandemic, scientists began to look for a cause of resistance to the Tamiflu medication. The cause was determined to be a histidine-to-tyrosine (amino acid) substitution at position 274 in its neuraminidase protein. As strains of influenza are continuously mutating, it is essential that scientists quickly and efficiently determine the correct neuraminidase subtype that is responsible for the drug resistance in order to develop medications that will combat specific strains of influenza. A new class of neuraminidase inhibitors that covalently attach to the enzyme have shown activity against drug-resistant virus in vitro.

Specificity In ideal circumstances, influenza virus neuraminidase (NA) should act on the same type of receptor the virus hemagglutinin (HA) binds to, a phenomenon that does not always happen. It is not quite clear how the virus manages to function when there is no close match between the specificities of NA and HA.

Exo- and endo- Neuraminidase enzymes can have endo- or exo-glycosidase activity, and are classified as EC 3.2.1.29 (endo-neuraminidase) and EC 3.2.1.18 (exo-neuraminidases). In general, mammalian sialic acid residues are at terminal positions (non-reducing end) in complex glycans, and so viral neuraminidases - which are exo-glycosidase enzymes - use these terminal residues as their substrates.

See also H5N1 genetic structure Antigenic shift Influenza research Hemagglutinin

References

External links

Influenza Research Database Database of influenza sequences (including neuraminidase). Proteopedia Influenza Neuraminidase, Tamiflu and Relenza Avian Influenza Neuraminidase, Tamiflu and Relenza

Illustrations

Worked examples

Example 1 — a first encounter with Viral neuraminidase

Start with the simplest possible case. Write down what Viral neuraminidase claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Viral neuraminidase before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Viral neuraminidase ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Viral neuraminidase

In research: Viral neuraminidase appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Viral neuraminidase in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Viral neuraminidase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 3.2.1, Glycoside hydrolase families, Influenza A virus, so understanding it makes those chapters shorter.
In everyday life: Look for Viral neuraminidase outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Viral neuraminidase in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Viral neuraminidase means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Viral neuraminidase out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Viral neuraminidase in simple terms?

Why does Viral neuraminidase matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Viral neuraminidase?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Viral neuraminidase.