science

Hemagglutinin esterase

Hemagglutinin esterase is a science 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 Hemagglutinin esterase rather than just read about it. In short: Hemagglutinin esterase (HEs) is a glycoprotein that certain enveloped viruses possess and use as an invading mechanism. HEs helps in the attachment and destruction of certain sialic acid receptors that are found on the host cell surface.

Key takeaways

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

Reference excerpt

Hemagglutinin esterase (HEs) is a glycoprotein that certain enveloped viruses possess and use as an invading mechanism. HEs helps in the attachment and destruction of certain sialic acid receptors that are found on the host cell surface. Viruses that possess HEs include influenza C virus, toroviruses, and coronaviruses of the subgenus Embecovirus (which does not include SARS-like coronaviruses). HEs is a dimer transmembrane protein consisting of two monomers, each monomer is made of three domains. The three domains are: membrane fusion, esterase, and receptor binding domains. The different HEs enzyme activities include: receptor binding activity, receptor hydrolysis (esterase) activity, and membrane fusion activity. The receptor binding activity involve the attachment of HEs to N-acetyl-9-O-acetylneuraminic acid (9-O-Ac- Neu5Ac) of glycolipids and glycoproteins and in turn serve as viral receptor. Receptor hydrolysis (esterase) activity allows virus particles to escape the infected cell by removing an acetyl group from the C9 position of terminal 9-O-Ac-Neu5Ac residues. Membrane fusion activity helps in incorporation viral genome into the host cell cytoplasm by enhancing the attachment between the viral envelope and host cell membrane. In certain influenza viruses, the cell surface consists of both hemagglutinin (HA) and neuraminidase (NA) proteins that encompass enzymatic activities, whereas hemagglutinin-esterase fusion (HEF) proteins have been found to be the primary single spike protein that combines all of the enzymatic activities listed above. HEF proteins have been tested to be high-temperature and low-pH resistant and are the primary source of virulence in viruses. Influenza C have been shown to have unique HEF structure proteins that enhance its ability to infect the host cell compared to influenza A and B. The folding of different domains in the hemagglutinin-esterase protein is important for intracellular transport of proteins from the endoplasmic reticulum to the Golgi apparatus. The presence of oligosaccharide chains in the E, F, and R domains of the HE enzyme also influence intracellular transport. Acylation of the hemagglutinin-esterase has shown to play an essential role in virus particle assembly replication. The exact process of enzyme catalytic cleavage has not yet been detailed out. However, proteolytic cleavage must occur before hemagglutinin-esterase membrane fusion activity. HEF proteins have a unique spikes hexagonal arrangement. This feature is unique to influenza C virus particles. The arrangement is a covering outside of the particle.

Structure Certain studies revealed that coronavirus and toroviruses HE was originated from HEF glycoprotein that is found in influenza C viruses which resulted from alteration of hemagglutinin esterase from a trimer into a dimer glycoprotein. During this process, the receptor destroying enzyme acetyl esterase domain stayed unchanged. However, the HE receptor binding domain has been altered in which that the ligand is bound in opposite orientation than before. Both coronavirus and toroviruses HE monomers are made up of the same three domains: central esterase/hydrolase domain, receptor binding lectin domain, and membrane proximal domain which is small. The two monomers of HE dimer in both CoV and ToV involve the same two contact regions (CR 1 and 2). CR 1 contain the receptor binding domain and contact region 2 that contain membrane proximal domain. Yet, ToV HE contacts region 2 contain additional esterase domain. As a result, the CR 2 surface is larger in ToV HEs than in CoV HEs. However, close to the carboxylic terminal membrane anchor, there are number of disulfide bridges between Cys385 of coronavirus HE that in turn keep the HE dimers connected to each other. In CoV HE, the two R domain beta sheets are connected to each other forming a continuous intermolecular beta sheet across the dimer interface. On the other hand, in ToV they are oriented at angles. As a result, the beta sheet of receptor binding domain in ToV is more twisted, the contact region 1 is smaller, and the R domains position are shifted along the Beta strands compared to CoV.

Crystalline structure "Initial studies using electron microscopy showed that the HEF spike forms a mushroom-shaped trimer consisting of a membrane-near stalk and a globular head". Later studies were able to examine and show a higher resolution structure (4.5 Å) of the hemagglutinin esterase fusion trimer using X-ray crystallography of the bromelain-cleaved ectodomain. Both hemagglutinin and hemagglutinin esterase fusion protein are similar in terms of structure and the folding of individual segments. yet, only 12% amino acid are identical between HA and HEF. One significant difference between HE and HEF is the presence of an additional bulge in HEF globular domain (bottom part of the domain) which contains the esterase region. The receptor-binding region in both HA and HEF is found in the upper part of the domain and contain only HEF1 residues. The stalk is made of three 60 Å long α- helices that contain: all sequences of HEF2 sequence, and certain HEF1 residues which are N-terminal residues (1–40), and C-terminal residues (367–432). The crystalline structure shows that the way that HEF binds to 9-O-Ac- Neu5Ac is the same as the way HA binds to Neu5Ac. The binding parts include an α-helix, a loop and an extended strand. There are hydrogen bonds between the amino acids (Tyr127, Thr170, Gly172, Tyr227 and Arg292) and the hydroxyl-groups of the ligand, and other residues form the structural support of the receptor binding site. A unique hydrophobic pocket is present in the HEF binding site that in turn accommodates the acetyl methyl group.

Activity

Receptor binding activity Glycolipids and glycoproteins contain N-acetyl-9-O-acetylneuraminic acid (9-O-Ac- Neu5Ac) that serve as viral receptor in which HEF binds to. HEF can bind to its receptor whether or not 9-O-Ac-Neu5Ac is attached by an α-2,3 or α-2,6 linkage to the next galactosyl residue. However, host specificity can be affected by terminal N-acetylneuraminic acid (Neu5Ac) and the glycosidic linkage of Neu5Ac. Influenza C virus can recognize 9-O-Ac-Neu5Ac on the surface of different cells due to its unique receptor specificity.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Hemagglutinin esterase

Start with the simplest possible case. Write down what Hemagglutinin esterase claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Hemagglutinin esterase 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 Hemagglutinin esterase 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 Hemagglutinin esterase

In research: Hemagglutinin esterase appears in science 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 Hemagglutinin esterase 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: Hemagglutinin esterase is common in secondary-school and first-year university syllabi. It links to neighbouring topics Viral enzymes, so understanding it makes those chapters shorter.
In everyday life: Look for Hemagglutinin esterase 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 Hemagglutinin esterase in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hemagglutinin esterase 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 Hemagglutinin esterase out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hemagglutinin esterase in simple terms?

Why does Hemagglutinin esterase matter?

Because it connects several science 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 Hemagglutinin esterase?

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 Hemagglutinin esterase.