InterPro domain: IPR034185

Site-1 peptidase (also known as SKI-1 or type I membrane-bound subtilisin-kexin-isoenzyme; MEROPS identifier S08.063) is a secretory Ca ²⁺ -dependent serine endopeptidase and a member of the subtilisin family S8, subfamily S8A [ 1 ]. It cleaves at nonbasic residues: Thr, Leu, and Lys. Site-1 peptidase plays a critical role in the regulation of the synthesis and metabolism of cholesterol and fatty acid metabolism [ 2 ].

The subtilisin family is one of the largest serine peptidase families characterised to date. Over 200 subtilises are presently known, more than 170 of which with their complete amino acid sequence [ 3 ]. It is widespread, being found in eubacteria, archaebacteria, eukaryotes and viruses [ 4 ]. The vast majority of the family are endopeptidases, although there is an exopeptidase, tripeptidyl peptidase [ 5 , 5 ]. Structures have been determined for several members of the subtilisin family: they exploit the same catalytic triad as the chymotrypsins, although the residues occur in a different order (HDS in chymotrypsin and DHS in subtilisin), but the structures show no other similarity [ 5 , 5 ]. Some subtilisins are mosaic proteins, while others contain N- and C-terminal extensions that show no sequence similarity to any other known protein [ 5 ].

1. Evolutionary families of peptidases. Biochem. J. 290 ( Pt 1), 205-18
2. The multifaceted proprotein convertases: their unique, redundant, complementary, and opposite functions. J. Biol. Chem. 288, 21473-81
3. Subtilases: the superfamily of subtilisin-like serine proteases. Protein Sci. 6, 501-23
4. Families of serine peptidases. Meth. Enzymol. 244, 19-61