Nidovirus Sialate-O-Acetylesterases

Abstract

Many viruses achieve reversible attachment to sialic acid (Sia) by encoding envelope glycoproteins with receptor-binding and receptor-destroying activities. Toroviruses and group 2 coronaviruses bind to O-acetylated Sias, presumably via their spike proteins (S), whereas other glycoproteins, the hemagglutinin-esterases (HE), destroy Sia receptors by de-O-acetylation. Here, we present a comprehensive study of these enzymes. Sialate-9-O-acetylesterases specific for 5-N-acetyl-9-Oacetylneuraminic acid, described for bovine and human coronaviruses, also occur in equine coronaviruses and in porcine toroviruses. Bovine toroviruses, however, express novel sialate-9-O-acetylesterases, which prefer the di-O-acetylated substrate 5-N-acetyl-7(8),9-di-O-acetylneuraminic acid. Whereas most rodent coronaviruses express sialate-4-O-acetylesterases, the HE of murine coronavirus DVIM cleaves 9-O-acetylated Sias. Under the premise that HE specificity reflects receptor usage, we propose that two types of Sias serve as initial attachment factors for coronaviruses in mice. There are striking parallels between orthomyxo-and nidovirus biology. Reminiscent of antigenic shifts in orthomyxoviruses, rodent coronaviruses exchanged S and HE sequences through recombination to extents not appreciated before. As for orthomyxovirus reassortants, the fitness of nidovirus recombinant offspring probably depends both on antigenic properties and on compatibility of receptor-binding and receptor-destroying activities.

Isolation and properties of two sialate-O-acetylesterases from horse liver with 4- and 9-O-acetyl specificities

“…This has also been reported from the rat liver esterase [46]. Only the esterase from bovine toroviruses hydrolyses a Sia with a 7-O-acetyl group, since it seems to prefer Sia di-O-acetylated at C-7 or C-8 and at C-9 of its side chain [29]. An explanation for Fig.…”

“…In contrast to these eukaryotic enzymes a variety of viruses were found to exhibit sialate esterase activities strongly specific for either 4-O-acetyl or 9-O-acetyl groups, respectively [28][29][30][31]. These Sia have receptor functions for these viruses.…”

“…The first example was the 9-O-acetyl-specific esterase isolated from influenza C virus and considered as a "receptor-destroying" enzyme [27,28]. Since then besides this orthomyxovirus such esterases were discovered in a variety of corona-and toroviruses, which preferentially hydrolyse either the 4-or 9-mono-O-acetylated or the sidechain di-O-acetylated Sia [29]. Several of these enzymes were cloned [30,31].…”

Assays of sialate-O-acetyltransferases and sialate-O-acetylesterases

“…Furthermore, a regulatory influence of these two enzymes on the expression of Neu5,9Ac 2 in E. coli [12] and group B Streptococcus [19] has been discussed. Sialate-O-acetylesterases have frequently been detected in animals of the deuterostome lineage, in bacteria and in viruses, some of which were partly or totally purified and the respective genes cloned [20][21][22][23][24]. The techniques of the analysis of SOAE activities will therefore be included.…”

Identification of a Sialate O-Acetyltransferase from Campylobacter jejuni

“…Therefore O-acetylated gangliosides could serve as targets for directed cancer therapies. O-Acetylation has contrasting effects on the process of viral attachment to membrane-bound sialoglycans; this is an obligatory modification for the association of some enteric and respiratory viruses but inhibits binding by others (8,9). As a final example, the sialylated polysaccharide capsules of group B Streptococcus (10), Escherichia coli K1 (11,12), and Neisseria meningitidis serogroups C, W-135, and Y (13) have been shown to be O-acetylated in some cases, which results in altered immunogenic properties.…”