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Sialic acid linked to glycoproteins and gangliosides is used by many viruses as a receptor for cell entry. These viruses include important human and animal pathogens, such as influenza, parainfluenza, mumps, corona, noro, rota, and DNA tumor viruses. Attachment to sialic acid is mediated by receptor binding proteins that are constituents of viral envelopes or exposed at the surface of non-enveloped viruses. Some of these viruses are also equipped with a neuraminidase or a sialyl-O-acetyl-esterase. These receptor-destroying enzymes promote virus release from infected cells and neutralize sialic acid-containing soluble proteins interfering with cell surface binding of the virus. Variations in the receptor specificity are important determinants for host range, tissue tropism, pathogenicity, and transmissibility of these viruses.

To investigate the role of cytoskeletal components in canine distemper virus (CDV) replication, various agents were used that interfere with turnover of actin filaments and microtubules. Only inhibition of actin filaments significantly reduced viral infectivity. Analysis of the intracellular localization of the viral matrix (M) protein revealed that it aligned along actin filaments. Treatment with actin filament-disrupting drugs led to a marked intracellular redistribution of M protein during infection as well as transfection. In contrast, the localization of the CDV fusion (F) protein was not significantly changed during transfection. Thus, a M protein-actin filament interaction appears to be important for generation of infectious CDV.

Bovine coronavirus (BCV) initiates infection by attachment to cell surface receptors the crucial component of which is N-acetyl-9-O-acetylneuraminic acid. Inactivation of receptors by neuraminidase treatment and restoration of receptors by enzymatic resialylation of asialo-cells is described as a method to determine (i) the type of sialic acid that is recognized; (ii) the linkage specificity of the viral binding activity; (iii) the minimal amount of sialic acid required for virus attachment. Evidence is presented that both glycoproteins and glycolipids can serve as receptors for BCV provided they contain 9-O-acetylated sialic acid. A model is introduced proposing that after initial binding to sialic acid-containing receptors, the S-protein of BCV interacts with a specific protein receptor. This interaction may result in a conformational change that exposes a fusogenic domain and thus induces the fusion between the viral and the cellular membrane.