O-acetylated sialic acids and neural infections

Research project P 14104 O-acetylated sialic acids and neural infection Reinhard VLASAK 24.01.2000 Glycosylation of proteins is an important modification with biological significance. One particular sugar present in many glycoproteins and glycolipids, sialic acid (neuraminic acid), is involved in cell recognition and modulation of immune responses. Sialic acid binding proteins in the brain are involved in maintenance of the myelin sheet, neurite outgrowth etc. Viruses in many instances use sialic acids as receptor determinants to infect target cells. We have recently identified a viral enzyme interacting specifically with 5-N-acetyl-4-0-acetyl sialic acid (Neu4,5AC2). This sialic acid is present in high concentrations in glycoproteins of guinea pigs and horses. The occurence in other animals is not studied in detail. Other forms of sialic acids are not recognized by this viral enzyme, which is present in murine coronavirus, which cause infection of the central nervous system. Several coronavirus strains containing the sialic acid-specific enzyme exhibit preference to infect neurons. Since one of the murine coronavirus strains used in our institute also binds to Neu4,5Ac2, we want to determine whether infection is mediated by this sialic acid. First, we want to define the substrate specificity of other coronavirus enzymes related to the murine viruses. By using a recombinant esterase protein, we want to determine the distribution of Neu4,5Ac2 in mice. In an international collaboration with Prof. Schauer (Univ. Kiel) the recombinant protein will be used to identifiy this sialic acid in other species. We will test neural cells for its presence as well. Employing two variants (with and without the sialic acid hydrolyzing enzyme) of puffinosis virus, which also infect mice, we want to determine the significance of the viral enzyme in infection of isolated neurons, oligodendrocytes, astrocytes and microglia cells. Furthermore, it will be tested whether cells derived from guinea pigs and horses can be infected with murine coronavirus. With recombinant virus-like particles, we want to determine whether the viral enzyme or the second surface protein, termed spike protein, is mediating binding to sialic acid. Last, but not least it will be tested whether puffinosis virus, which was originally isolated in 1982 from Manx shearwater (Puffinus puffinus) is really an avian virus. Due to the isolation procedure it may be a murine coronavirus strain. During the next outbreak of "puffinosis" tissue samples will be collected from dead animals found on the island of Skomer offshore the coast of Wales and transported to our institute. Here the samples will be tested for presence of viral genes by a combination of reverse transcription and polymerase chain reaction. In case we can proof the origin of the virus, a natural reservoir for coronaviruses would be identified.