Expression of cDNA encoding the human “protective protein≓ associated with lysosomal β-galactosidase and neuraminidase: Homology to yeast proteases

A small pool of phosphorylated PPCA precursor can be recovered extracellularly, but this secreted form can be re-internalized via mannose-6-phosphate receptor-mediated endocytosis and routed to lysosomes where it becomes catalytically active.

“A small pool of phosphorylated precursor can also be recovered extracellularly, but this secreted form can be re-internalized by cells via mannose-6-phosphate receptor-mediated endocytosis and routed to the lysosomes where it becomes catalytically active as the de novo synthesized enzyme 5,6.”

In the absence of functional PPCA, NEU1 is retained in the endosomal compartment while the pool of β-GAL reaching lysosomes is rapidly degraded; formation of the PPCA/NEU1/β-GAL complex has a reciprocal advantage for the three enzymes, which acquire active and stable conformation in lysosomes.

“In absence of functional PPCA, NEU1 is retained in the endosomal compartment while the pool of β-GAL reaching the lysosomes is rapidly degraded 36.”

NEU1 requires an accessory protein for activity-the protective protein cathepsin A (CTSA; PPCA).

“NEU1 is unique among all known mammalian, microbial, or viral sialidases, as it requires an accessory protein for activity—the protective protein cathepsin A (CTSA; PPCA) (12, 19–23).”

NEU1 is unique among all known sialidases in that it requires an accessory protein for activity.

“NEU1 is unique among all known mammalian, microbial, or viral sialidases, as it requires an accessory protein for activity—the protective protein cathepsin A (CTSA; PPCA) (12, 19–23).”