Lysosomal neuraminidase : a unique member of the sialidase superfamily

Lysosomal neuraminidase initiates the hydrolysis of oligosaccharldes, gangliosides, glycolipids and glycoprotelns by removing their terminal sialic acid residues. The enzyme functions exclusively In a multi-enzyme complex, together with flgalactosidase and protective protein/cathepsin A (PPCA) and Is dependent for Its activity and stability on the latter protein. Mutations In the neuraminidase gene are the basis for the lysosomal storage disorder sialidosls, while mutations In the PPCA gene Indirectly results In the Impairment of neuraminidase and p·galactosidase activity, causing the lysosomal storage disorder galactoslalldosls. The experimental work that is described in this thesis involves the Isolation and characterization of the cDNA's encoding human and mouse lysosomal neuraminidase. Structural and functional analysis of this enzyme has focused on the Interaction with PPCA in relation to Its transport to the Iysosomes and the mechanism of catalytic activation. These studies, In combination with the Identification and functional analysis of a large number of novel mutations In slalidosls patients, have given new Insights Into the biochemical functions and properties of neuraminidase and provided reliable phenotype-genotype correlations. The results presented In this thesis may form the basis for understanding the structural characteristics of this unusual lysosomal protein and for the future development of strategies for therapy of both slalldosis and galactoslalldosis patients.