Protective protein appears to be essential for both the activity of beta-galactosidase and neuraminidase, it associates with these enzymes and exerts a protective function necessary for their stability and activity. This protein is also a carboxypeptidase and can deamidate tachykinins. Release of a C-terminal amino acid with broad specificity. Heterodimer of a 32 kDa chain and a 20 kDa chain; disulfide-linked. Belongs to the peptidase S10 family.