Sialidase activity

The sialidase active site contains a relatively high number of charged amino acids and, in total, there are ten polar (Arg/Asp/Glu) and four non-polar residues that... 

Fig. 4 The influenza A viras sialidase active site showing some key interactions...

Analysis of Potential Binding Interactions within the Influenza Virus Sialidase Active Site... 

Fig. 7 The influenza virus A sialidase active site showing the five potential inhibitor binding subsites (with S5 containing the hydrophobic pocket formed by reorientation of the Glu276 side-chain), with oseltamivir carboxylate 18 placed in the active site...

An interesting feature of the influenza virus sialidase active site that offers the potential for developing inhibitors specific for N1 sialidases, including avian influenza A/H5N1 virus sialidase, has recently been revealed by X-ray crystallography. The... 

Viruses that contain amino acid substitutions in the sialidase that impart resistance to the developed inhibitors have been isolated from serial passage of virus in the presence of drug in cell culture and from the clinical setting (reviewed in McKimm-Breschkin 2000 Zambon and Hayden 2001 Cinatl et al. 2007a Reece 2007). In addition, influenza B virus variants with reduced drug sensitivity have been isolated from previously untreated patients (Hurt et al. 2006 Hatakeyama et al. 2007). The types of mutations that are observed are sub-type specific. The mutations present in variants isolated from clinical samples are shown in Table 1, and their locations within the sialidase active site are shown diagrammatically in Fig. 9. 

Strain Mutation Drug Level of sialidase activity and/or viral fitness... 

Usuki, S., Hoops, P., and Sweeley, C. C. (1988). Growth control of human foreskin fibroblasts and inhibition of extracellular sialidase activity by 2-deoxy-2,3-dehydro-N-acetylneura-minic acid. /. Biol. Chem. 263, 10595-10599. 

Several ganglioside analogs containing an a-thioglycoside of sialic acid, derived for example from (29 c) (Scheme 8), have been found to be potent inhibitors of sialidase activities of different subtypes of influenza virus [64]. 

Variable sialidase activities are known to occur physiologically during ontogenesis."0 In chick retina, the lowest enzyme activity was observed in the 8-day-old embryo, whereas the highest activity was measured at hatching. Gangliosides were shown to be the best substrates... 

Sialidase activity (nmol/mg protein/h) /Ygalactosidasc activity (nmol/mg protein/h)... 

Exposure of HeLa cells to butyrate had no effect on the activity of GM3-sialidase when GM3 specifically labeled in the sialic acid residue was used as substrate (Fig. 3a). We were unable to detect any "ecto"-sialidase activity in either control or butyrate-treated cells (14) although others have postulated that such an enzyme is important in regulating plasma membrane gangliosides (15,16). In contrast, the activity of the specific sialyl transferase involved in GM3 biosynthesis increased over 20-fold following butyrate treatment (Fig. 3b). The effect was specific as activities of the other glycosphingolipid transferases that could be measured in HeLa cells were not altered in butyrate-treated cells (4,8,17). 

HeLa cells were cultured for 24 hr with (open bars) and without (closed bars) 5 mM sodium butyrate, harvested, and assayed for indicated enzyme activity. A GM3-sialidase activity assayed with GM3 specifically labeled with [,iC]- N-acetylneuraminic acid as substrate ("14JJ. B Sialyltrasferase activity assayed with CMP-[, acetylneuraminic acid and lactosylceramide as substrates, and synthesis of labeled GM3 determined (17). Data... 

Fig. 3. A schematic representation of some key interactions of Neu5Ac2en 5 with conserved influenza virus A sialidase active site residues.

To facilitate the description of the binding between a-Neu5Ac and NA, the influenza virus sialidase active site can be divided into five regions (Fig. 17.7) [31,69], Subsite 1... 

FIGURE 17.12 Interaction of oseltamivir carboxylate (20) with the influenza virus sialidase active site. 

FIGURE 17.16 Comparison of group 1 and group 2 sialidase active sites, (a) Oseltamivir carboxylate binds into the open catalytic site of group 1 sialidase Nl. (b) Binding between oseltamivir carboxylate and group 2 sialidase N9 with the closed 150-loop. 

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