This review focuses on the biological role and clinical relevance of relatively poor studied enzymes
known as sialidases. We describe structure and function of sialic acid, in particular as a component of gangliosides
and plasma lipoproteins. Several types of sialidases are known in mammals, of which trans-sialidase is of
special interest, since it is capable of removing sialic acid from low density lipoprotein (LDL) particles and transferring
it to different acceptors in blood plasma. Desialylation of LDL, in turn, endows it a capacity to accumulate
in the smooth muscle cells of human aortic intima, and therefore is important for atherogenesis. Moreover, sialidases
appear to be involved in a variety of pathological processes, including viral infections and cancer, which
makes these enzymes an attractive therapeutic target.