Viral Lectins for the Detection of 9-O-Acetylated Sialic Acid on Glycoproteins and Glycolipids

A number of viruses are able to recognize specific carbohydrate structures and to use these structures for the attachment to the cell surface. Influenza C virus and bovine coronavirus specifically attach to receptors containing N-acetyl-9-O-acetylneuraminic acid. Therefore, they can be used as lectins for the detection of glycoconjugates containing this type of sialic acid. These viruses also contain an acetylesterase on their surface which can be exploited for the detection of virions bound to immobilized glycoconjugates (Zimmer et al. 1992). As shown in Fig. 1, in the case of influenza C virus the acetylesterase activity is a function of the surface glycoprotein HEF that also mediates the binding to N-acetyl-9-O-acetylneuraminic acid. In the case of bovine coronavirus the acetylesterase is a function of the HE protein. Though this protein also recognizes 9-O-acetylated sialic acid, the binding of virus is primarily due to a another surface glycoprotein designated S (Schultze et al. 1991). The esterases of both viruses are able to cleave the synthetic substrate α-naphthyl acetate giving rise to naphthol. The latter compound reacts with a diazonium ion such as Fast Red resulting in a coloured insoluble complex, which reveals the presence of bound virus.