Which lysosomal enzyme degrades complex polysaccharides?
Lysosomal lumen houses a consortium of about sixty acid hydrolases tailored to distinct macromolecular classes, all evolutionarily optimized for acidic pH and limited activity at neutral pH to protect cell. Among them, glycosidases or glycoside hydrolases hydrolyze glycosidic linkages in oligosaccharides, N-linked glycoproteins, glycolipids and glycosaminoglycans. Examples include acid alpha-glucosidase removing alpha-1,4 linkages in glycogen, beta-galactosidase cleaving galactose from GM1 ganglioside, alpha-mannosidase, neuraminidase, fucosidase, and hexosaminidases A and B that degrade GM2 ganglioside and heparan sulfate. These enzymes sequentially trim sugar residues from non-reducing ends in highly ordered fashion, requiring preceding action by other enzymes and sulfatases to complete degradation. Synergism with sialidases that remove terminal sialic acids is needed for access. Deficiencies lead to lysosomal storage disorders such as Tay-Sachs due to hexosaminidase A loss causing GM2 accumulation in neurons, Pompe disease with acid alpha-glucosidase deficiency leading to glycogen storage in muscle, and mucopolysaccharidoses from glycosaminoglycan buildup. Combined activities with proteases, lipases, nucleases, phosphatases and sulfatases complete catabolism into monosaccharides effluxed via sugar transporters like sialin.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 13: Lysosomal Hydrolases – Glycosidases.