Exo-alpha-sialidase that catalyzes the hydrolytic cleavage of the terminal sialic acid (N-acetylneuraminic acid, Neu5Ac) of a glycan moiety in the catabolism of glycolipids, glycoproteins and oligosacharides. Efficiently hydrolyzes gangliosides including alpha-(2->3)-sialylated GD1a and GM3 and alpha-(2->8)-sialylated GD3 (PubMed:19506080, PubMed:22393058). Hydrolyzes poly-alpha-(2->8)-sialylated neural cell adhesion molecule NCAM1 likely at growth cones, suppressing neurite outgrowth in hippocampal neurons (PubMed:19506080, PubMed:22393058). May desialylate sialyl Lewis A and X antigens at the cell surface, down-regulating these glycan epitopes recognized by SELE/E selectin in the initiation of cell adhesion and extravasation (By similarity). Has sialidase activity toward mucin, fetuin and sialyllactose (PubMed:19506080, PubMed:22393058). Hydrolysis of alpha-(2->3)-, alpha-(2->6)-, alpha-(2->8)- glycosidic linkages of terminal sialic acid residues in oligosaccharides, glycoproteins, glycolipids, colominic acid and synthetic substrates. ganglioside GM3 + H2O = beta-D-galactosyl-(1->4)-beta-D-glucosyl-(1<->1)-ceramide + N-acetylneuraminate ganglioside GM3 (d18:1(4E)) + H2O = a beta-D-Gal-(1->4)-beta-D-Glc-(1<->1)-Cer(d18:1(4E)) + N-acetylneuraminate ganglioside GM2 + H2O = N-acetyl-beta-D-galactosaminyl-(1->4)-beta-D-galactosyl-(1->4)-beta-D-glucosyl-(1<->1')-ceramide + N-acetylneuraminate ganglioside GM2 (d18:1(4E)) + H2O = ganglioside GA2 (d18:1(4E)) + N-acetylneuraminate ganglioside GD1a + H2O = ganglioside GM1 + N-acetylneuraminate ganglioside GD1a (d18:1(4E)) + H2O = ganglioside GM1 (d18:1(4E)) + N-acetylneuraminate ganglioside GD3 + H2O = ganglioside GM3 + N-acetylneuraminate ganglioside GD3 (d18:1(4E)) + H2O = ganglioside GM3 (d18:1(4E)) + N-acetylneuraminate Optimum pH is 4.4-6.5. Highly expressed in brain, particularly in hippocampus, and at lower levels in liver and spleen. Expressed in hippocampal neurons (at protein level). Expressed at low levels in embryonic brain, then rapidly up-regulated after birth reaching a maximum at postnatal day 14, followed by a decrease. Down-regulated upon neuron differentiation. Belongs to the glycosyl hydrolase 33 family.