Short name: Saposin
Overlapping homologous superfamilies
- Saposin (IPR008373)
- Saposin, chordata (IPR021165)
Sphingolipids are bioactive compounds found in lower and higher eukaryotes. They are involved in the regulation of various cellular functions, such as growth, differentiation and apoptosis, and are believed to be essential in a healthy diet. Sphigolipids are degraded in the lysosome, and the products from their hydrolysis are used in other biosynthetic and regulatory pathways in the host.
There are a number of lysosomal enzymes involved in the breakdown of sphinogolipids, and these act in sequence to degrade the moieties [PMID: 2515150]. These enzymes require co-proteins called sphingolipid activator proteins, (SAPs or saposins), to stabilise and activate them as necessary. SAPs are non-enzymatic and usually have a low molecular weight. They are conserved across a wide range of eukaryotes and contain specific saposin domains that aid in the activation of hydrolase enzymes. There have been four human saposins described so far, sharing significant similarity with each other and with other eukaryotic SAP proteins.
Mutations in SAP genes have been linked to a number of conditions. A defect in the saposin B region leads to metachromatic leucodystrophy (MLD), while a single nucleotide polymorphism in the SAP-C region may give rise to Gaucher disease [PMID: 2019586]. More recently, an opportunistic protozoan parasite protein has shown similarity both to the higher and lower eukaryotic saposins. The pore-forming protein isolated from virulent Naegleria fowleri (Brain eating amoeba) has been dubbed Naegleriapore A. It also shares structural similarity with cytolytic bacterial peptides, although this similarity does not extend to the sequence level.
- PR01797 (SAPOSIN)