REVIEW Mammalian sialidases: Physiological and pathological roles in cellular functions

Sialic acids are terminal acidic monosaccharides, which in-fluence the chemical and biological features of glycoconju-gates. Their removal catalyzed by a sialidase modulates various biological processes through change in conform-ation and creation or loss of binding sites of functional molecules. Sialidases exist widely in vertebrates and also in a variety of microorganisms. Recent research on mam-malian sialidases has provided evidence for great import-ance of these enzymes in various cellular functions, including lysosomal catabolism, whereas microbial siali-dases appear to play roles limited to nutrition and patho-genesis. Four types of mammalian sialidases have been identified and characterized to date, designated as NEU1, NEU2, NEU3 and NEU4. They are encoded by different genes and differ in major subcellular localization and en-zymatic properties including substrate specificity, and each has been found to play a unique role depending on its particular properties. This review is an attempt to concisely summarize current knowledge concerning mammalian sialidases, with an especial focus on their properties and physiological and pathological roles in cellular functions