A microplate assay for sialidase activity using plant lectin binding to N-acetyllactosamine

This paper presents a sensitive assay for sialidase activity based on the specific binding of lecting to N-acetyllactosamine. The substrate used for sialidase assay is fetuin (30-100 ng/50 microliters) with sialylated oligosaccharides, which was then coated on a 96-well microtiterplate. After removing sialic acids from the terminal positions of the glycoconjugate glycans by sialidase, it was subjected to biotin-labeled lectin (Ricinus communis agglutinin 120), which binds specifically to N-acetyllactosamine. This was followed by the addition of a peroxidase conjugated avidin-biotin complex. The amount of bound peroxidase was determined by a colorimetric assay. The sensitivity was enhanced 1000- to 10,000-fold compared to the colorimetric assay using a synthetic substrate such as 2-O-(p-nitrophenyl)-N-acetyl-alpha-D-neuraminic acid (PNPN). In the established method, only very small amounts of substrate and sialidase were required; therefore, it can be applied to the quantitative assay of some sialidases from Vibrio cholerae, streptococcus, the influenza virus and rat liver.