Isolation and Characterization of the Acetylesterase of Hemagglutinating Encephalomyelitis Virus (HEV)
Receptor-destroying enzymes have long been thought to be present only on influenza viruses and paramyxoviruses but not on other animal viruses. Paramyxoviruses as well as influenza A and B viruses are able to inactivate their own receptors by virtue of a neuraminidase which cleaves terminal sialic acid from glycoproteins or gangliosides (Drzeniek, 1972). The corresponding enzyme of influenza C virus is a sialate 9-0-acetylesterase which releases acetyl residues from position C-9 of N-acetyl-9-O-acetyl-neuraminic acid (Neu5,9Ac2) (Herrler et al., 1985). Recently, sequencing of the genome of mouse hepatitis virus revealed an open reading frame which surprisingly showed some similarity to the glycoprotein HEF of influenza C virus (Luytjes et al., 1988). This finding prompted a search which resulted in the discovery that bovine Coronavirus (BCV) contains a sialate O-acetylesterase similar to the receptor-destroying enzyme of influenza C virus (Vlasak et al., 1988a). This enzyme is inhibited by diisopropylfluorophos-phate (DFP), which binds covalently to serine in the active-site of serine proteases and esterases. By using a radioactive form of this inhibitor protein E3 of BCV was identified as esterase (Vlasak et al., 1988b). The same glycoprotein has been shown previously to be involved in the hemagglutinating activity of BCV (King et al., 1985). Therefore, E3 is designated HE.
KeywordsEsterase Activity Hemagglutinating Activity Neuraminic Acid Mouse Hepatitis Virus Terminal Sialic Acid
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