Neuraminidase
Encyclopedia
Glycoside hydrolase
Glycoside hydrolases catalyze the hydrolysis of the glycosidic linkage to release smaller sugars...
enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s that cleave the glycosidic linkages of neuraminic acid
Neuraminic acid
Neuraminic acid is a 9-carbon monosaccharide, a derivative of a ketononose. Neuraminic acid may be visualized as the product of an aldol-condensation product of pyruvic acid and D-mannosamine...
s. Neuraminidase enzymes are a large family, found in a range of organisms. The most commonly known neuraminidase is the viral neuraminidase
Viral neuraminidase
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...
, a drug target for the prevention of the spread of influenza
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
infection. The viral neuraminidases are frequently used as an antigenic determinants found on the surface of the Influenza
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
virus. Some variants of the influenza neuraminidase confer more virulence to the virus than others. Other homologs are found in mammalian cells, which have a range of functions. At least four mammalian sialidase homologs have been described in the human genome
Human genome
The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs plus the small mitochondrial DNA. 22 of the 23 chromosomes are autosomal chromosome pairs, while the remaining pair is sex-determining...
(see NEU1
NEU1
Sialidase 1 , also known as NEU1 is a mammalian lysosomal neuraminidase enzyme which in humans is encoded by the NEU1 gene.- Function :...
, NEU2
NEU2
Sialidase-2 is an enzyme that in humans is encoded by the NEU2 gene.-Further reading:...
, NEU3
NEU3
Sialidase-3 is an enzyme that in humans is encoded by the NEU3 gene.-Further reading:...
, NEU4
NEU4
Sialidase-4 is an enzyme that in humans is encoded by the NEU4 gene.-Further reading:...
).
Neuraminidases, also called sialidases, catalyze the hydrolysis of terminal sialic acid
Sialic acid
Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone. It is also the name for the most common member of this group, N-acetylneuraminic acid...
residues from the newly formed virions and from the host cell receptors. Sialidase activities include assistance in the mobility of virus particles through the respiratory tract mucus and in the elution of virion progeny from the infected cell.
Reaction
There are two major classes of Neuraminidase that cleave exo or endo poly-sialic acids:- Exo hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)-glycosidic linkages of terminal sialic acid residues
- Endo hydrolysis of (2→8)-α-sialosyl linkages in oligo- or poly(sialic) acids
Subtypes
Swiss-Prot lists 137 types of neuraminidase from various species . Nine subtypes of influenza neuraminidase are known; many occur only in various species of duck and chicken. Subtypes N1 and N2 have been positively linked to epidemics in man, and strains with N3 or N7 subtypes have been identified in a number of isolated deaths.
The following is a list of major classes of neuraminidase enzymes:- Viral neuraminidaseViral neuraminidaseViral neuraminidase is a type of neuraminidase found on the surface of influenza viruses that enables the virus to be released from the host cell...
- Bacterial neuraminidaseBacterial neuraminidaseBacterial neuraminidase is type of neuraminidase and a virulence factor for many bacteria including Bacteroides fragilis and Pseudomonas aeruginosa....
- Mammalian neuraminidases:
Structure
InfluenzaInfluenzaInfluenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
neuraminidase exists as a mushroom-shape projection on the surface of the influenza virus. It has a head consisting of four co-planar and roughly spherical subunits, and a hydrophobic region that is embedded within the interior of the virus' membrane. It comprises a single polypeptide chain that is oriented in the opposite direction to the hemagglutinin antigen. The composition of the polypeptide is a single chain of six conserved polar amino acids, followed by hydrophilic, variable amino acids. β-sheets predominate as the secondary level of protein conformation.
Recent emergence of oseltamivirOseltamivirOseltamivir INN , an antiviral drug, slows the spread of influenza virus between cells in the body by stopping the virus from chemically cutting ties with its host cell; median time to symptom alleviation is reduced by 0.5–1 day. The drug is sold under the trade name Tamiflu, and is taken orally...
and zanamivir resistant human influenza A(H1N1H1N1'Influenza A virus is a subtype of influenza A virus and was the most common cause of human influenza in 2009. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza. H1N1 strains caused a few percent of...
) H274Y has emphasized the need for suitable expression systems to obtain large quantities of highly pure and stable, recombinantRecombinantRecombinant may refer to:* A recombinant organism - an organism that contains a different combination of alleles from either of its parents.* Recombinant DNA - a form of artificial DNA* Recombinant virus - a virus formed by recombining genetic material...
neuraminidase through two separate artificial tetramerization domains that facilitate the formation of catalytically active neuraminidase homotetramers from yeastYeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
and StaphylothermusStaphylothermusIn taxonomy, Staphylothermus is a genus of the Desulfurococcaceae.-External links:...
marinus, which allow for secretion of FLAG-tagFLAG-tagFLAG-tag, or FLAG octapeptide, is a polypeptide protein tag that can be added to a protein using recombinant DNA technology. It can be used for affinity chromatography, then used to separate recombinant, overexpressed protein from wild-type protein expressed by the host organism...
ged proteins and further purification.
Mechanism
The enzymatic mechanism of influenza virus sialidase has been studied by Taylor and coworkers, shown in Figure 1. The enzyme catalysis process has four steps. The first step involves the distortion of the α-sialoside from a 2C5 chair conformation (the lowest-energy form in solution) to a pseudoboat conformation when the sialoside binds to the sialidase. The second step leads to an oxocarbocation intermediate, the sialosyl cation. The third step is the formation of Neu5Ac initially as the α-anomer, and then mutarotation and release as the more thermodynamically-stable β-Neu5Ac.
Inhibitors
Neuraminidase inhibitorNeuraminidase inhibitorNeuraminidase inhibitors are a class of antiviral drugs targeted at the influenza virus, which work by blocking the function of the viral neuraminidase protein, thus preventing the virus from reproducing by budding from the host cell....
s are useful for combating influenzaInfluenzaInfluenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
infection: zanamivir, administered by inhalation; oseltamivirOseltamivirOseltamivir INN , an antiviral drug, slows the spread of influenza virus between cells in the body by stopping the virus from chemically cutting ties with its host cell; median time to symptom alleviation is reduced by 0.5–1 day. The drug is sold under the trade name Tamiflu, and is taken orally...
, administered orally; and under research is peramivirPeramivirPeramivir is an experimental antiviral drug developed by BioCryst Pharmaceuticals for the treatment of influenza. It has been authorized for the emergency use of treatment of certain hospitalized patients with known or suspected 2009 H1N1 influenza....
administered parenterally, that is through intravenous or intramuscular injection.
There are two major proteins on the surface of influenza virus particles. One is the lectin haemagglutinin protein with three relatively shallow sialic acid-binding sites and the other is enzyme sialidase with the active site in a pocket. Because of the relative deep active site in which low molecular weight inhibitors can make multiple favorable interactions and approachable methods of designing transition state analogues in the hydrolysis of sialosides, the sialidase becomes more attractive anti-influenza drug target than the haemagglutinin. After the X-ray crystal structures of several influenza virus sialidases were available, the structure-based inhibitor design was applied to discover potent inhibitors of this enzyme.
The unsaturated sialic acid (N-acetylneuraminic acid [Neu5ac]) derivative 2-deoxy-2, 3-didehydro-D-N-acetylneuraminic acid (Neu5Ac2en), a sialosyl cation transition-state (Figure 2) analogue, is believed the most potent inhibitor core template.
To prepare structurally modified Neu5Ac2en derivatives may give more effective inhibitors.
Many Neu5Ac2en-based compounds have been synthesized and tested for their influenza virus sialidase inhibitory potential. For example:
The 4-substituted Neu5Ac2en derivatives (Figure 3), 4-amino-Neu5Ac2en (Compound 1), which showed two orders of magnitude better inhibition of influenza virus sialidase than Neu5Ac2en5 and 4-guanidino-Neu5Ac2en (Compound 2), known as Zanamivir, which is now marketed for treatment of influenza virus as a drug, have been designed by von Itzstein and coworkers. A series of amide-linked C9 modified Neu5Ac2en have been reported by Megesh and colleagues as NEU1 inhibitors.
External links
- Orthomyxoviruses, Robert B. Couch, UTMB. Article includes a good clear line drawing of a neuraminidase on an influenza virus.
- Viral neuraminidase