Neuraminidases Sialidases

10 Sialidases (Neuraminidases). The three sialidase families (GH 33, 34 and 83) all have the same catalytic machinery, an aspartate, which appears to act as a proton donor, and a probable nucleophilic tyrosine, rather than a carboxylate, activated in all likelihood by a glutamate. GH 33 contains all transialidases as well as simple hydrolytic enzymes, whereas GH 34 and GH 83 contain only enzymes from viruses which are mammalian or avian pathogens. GH 33 and GH 34 act with retention of the anomeric configuration and it is currently assumed that GH 83 is similar. Obtaining crystal structures with mechanistically informative ligands bound is complicated by the facility with which sialidases dehydrate A -acetylneuraminic acid to its 2,3-dehydro derivative, DANA the process is most facile with GH 33 enzymes. The influenza sialidase in GH 34 was more amenable and not only bound the minor anomer of NANA, but bound it in the conformation. Structures of GH 83 sialidases are available only with uninformative ligands such as p-NANA bound. 

A similar situation to that with the lytic transglycosylases occurs with a leech sialidase (sialidase L), which gives 2,7-anhydro-A-acetylneuraminic acid, despite being in GH 33 like all other non-viral sialidases and transialidases. This enzyme binds a C-glycoside substrate-analogue (aNeuNAc-CH2-CH=CH2) and product in the conformation. The conformation of glycosyl-enzyme 

The similarity of the /iig values obtained for the acid-catalytic mutant of the M. viridifaciens enzyme and wild-type V. cholerae, S. typhimurium, influenza and M. decora enzymes confirm indicate that, at least with unnatural, activated substrates the application of acid catalysis is minimal. Further evidence is the high intrinsic leaving group effects, suggesting that the loss of bonding between C2 and 02 is not offset by partial protonation. 

Very remarkably, site-directed mutagenesis of the supposedly nucleophilic tyrosine of the GH 33 sialidase from Micromonospora viridifaciens yields enzymes which still work, and some of them act with inversion, rather than retention. A detailed examination of the inverting Y 370G mutant revealed that the hole left by removal of the tyrosine side-chain was now filled with water molecules surprisingly, the effect of removing the nucleophilic tyrosine 

Levansucrase is a transfructosylase which converts sucrose to levan , a largely p(2 6)-linked fructofuranose polymer, and has been investigated because of its synthesis by oral bacteria. The levans and dextrans produced from dietary sucrose are sparingly water soluble and contribute to the build-up of dental plaque on the teeth. The enzyme from Bacillus subtilis was shown to have ping-pong kinetics,and the intermediacy of a covalent, fructosylated 

---

An overview of the role of the virus-associated glycoprotein sialidase (neuraminidase) and some of the most recent developments towards the discovery of anti-influenza drugs based on the inhibition of influenza virus sialidase is provided in this chapter. 

Achyuthan KE, Achyuthan AM (2001) Comparative enzymology, biochemistry and pathophysiology of human cxo-alpha-sialidases (neuraminidases). Compar Biochem Physiol B Biochem Mol Biol 129 29-64... 

Mucolipidoses Sialidosis MU Sialidase (neuraminidase) Glycoprotein fragments... 

There are other lysosomal disorders in addition to those shown in Figure 9.20 and Table 9.1. For instance, several types of fucosidoses exist, which affect such structures as glycoproteins and blood group substances. Sialidoses also exist. However, lysosomal fucosidase and sialidase (neuraminidase) deficiencies do not affect the degradation of gangliosides. 

Sialidase. Neuraminidase. N-acylneuraminate glycohydrolase. Alpha-neuraminidase. 

Glycoprotein sialidase (neuraminidase) (EC 3.2.1.18). Other lysosomal activities in liver sometimes increased. Sialyloligosaccharides accumulate. Mental retardation, skeletal abnormalities and Hurler-type facial features may be present in varying degrees, or absent. Hepatosplenomegaly, renal involvement and hydrops fetalis sometimes present. 

Animal V. The first stage of infection is adsorption of the vims to the exterior surface of the animal cell membrane. Adsorption occurs by interaction between a virus-coded protein on the surface of the virion and a receptor moleeule on the cell membrane. Most cell receptors are glycoproteins. Moreover, they are normal membrane glycoproteins with specific functions unrelated to virus infection. The interaction is specific. Thus, the binding protein of influenza virus interacts with the o2 3 linked terminal sialic add residue of the host cell membrane glycopFOtein treatment of a cell with sialidase (neuraminidase) renders it resistant to infection, and glycoproteins with al 6 linked siaUc acid do not serve as receptors. Under natural conditions, the presence of appropriate receptor molecules on the cell membrane is a precondition for virus infection, i.e. in the absence of receptors, the cell is not permissive for virus infection... 

Woods, JA4., Bethell, R.C., Coates, J.A.V., Healy, N., Hiscox, S.A., Pearson, BA., Ryan, DA4., Ticehurst, J., Tilling, J., Walcott, S.M., and Penn, CJl. (1993) 4-Guanidino-2,4-dideoxy-23-dehydro-Af-acetylneuraminic acid is a highly effective inhibitor both of the sialidase (neuraminidase) and of growth of a wide range of influenza A and influenza B viruses in vitro. Antimicrobial... 

Exosialidases (exo-a-sialidase, neuraminidase) are hydrolases chopping off terminal residues from the non-reducing end of glycans... 

Warren, L., and Spearing, C. W., 1960, Mammalian sialidase (neuraminidase), Biochem. Biophys. Res. Commun. 3 489-492. 

It is not surprising that free sialic acid can be found in human feces since there is present considerable amounts of sialidase (neuraminidase), probably of bacterial origin (unpublished). 

Sialidase (neuraminidase, N-acetylneuraminosyl glycohydrolase, EC 3.2.1.18) catalyzes the hydrolysis of sialic acid from sialic-acid-contain-ing glycoproteins, glycolipids, and oligo- and polysaccharides. Sialidases recently have attracted very wide interest. 

Seto, J. T., 1964, Sialidase (neuraminidase) activity of standard and incomplete virus, Biochim. Biophys. Acta 90 420-427. 

---