Here we describe a novel approach to sialidase activity estimation. Sialidases (EC 184.108.40.206, exo-α-sialidases), also
known as neuraminidases, are the group of enzymes, which hydrolyze the glycoside bound between terminal sialic acid
and subsequent carbohydrate residue in glycoproteins and glycolipids. Sialic acids are the group of monosaccharides
with acidic properties, since they are acetylated or glycolylated derivates of neuraminic acid. Flu and some other viruses
use neuraminidase activity to infect host cells. The level of sialylation was shown to be tightly connected with tumor cell
invasiveness and metastatic potential, sialylation level also determines the clearance of aged or virus-infected cells. Thus,
detection of sialidase activity is of primary importance for clinical diagnostics as well as life science research.
The authors developed the assay for both visualization and estimation of sialidase activity in living cells. Previously
known methods for sialidase activity detection required destruction of cellular material, or were low-sensitive, or
provided no information on the activity localization in certain intracellular compartment. To overcome these problems, a
fluorogenic neuraminidase substrate, 4-MUNA was utilized, and the method for detection of neuraminidase activity
using fluorescent microscopy was proposed, it provided a high signal level and information on cellular localization of the
studied enzyme. By using this approach the increase of sialidase activity on apoptotic cells was demonstrated in
comparison to viable and primary necrotic cells.