Properties of and a New Technique for Fluorescent Detection of Influenza Virus Sialidase

Abstract

Influenza A virus (IAV) has two envelope glycoproteins, hemagglutinin (HA) and neuraminidase (NA). HA recognizes sialic acids at the terminals of glycan chains on the host cell surface as virus receptors. NA shows sialidase activity, which cleaves sialic acids from the terminals of glycan chains. The viral sialidase activity is well-known to facilitate release of progeny virus from the host cell surface by preventing virus binding to sialic acid. Low-pH stability of viral sialidase activity is a unique property for pandemic IAV NAs distinct from most epidemic IAVs. It is thought that the low-pH stability of sialidase activity contributes to the spread of infection in a pandemic of a new subtype of IAV through enhancement of virus replication. Recently, a new sialidase substrate has been developed for histochemical fluorescent visualization of viral sialidase activity. This substrate can visualize living IAV-infected cells abundantly expressing viral NA by an easy protocol in a short time. The properties and functions of IAV sialidase activity, mainly in terms of low-pH stability, and a new tool for detection of IAV sialidase activity are described in this review.