Source: Active recombinant N-terminal His-tagged enzyme isolated from a HEK293 overexpression system ? MW: 71 kDa (~16 & 63 kDa purified) ? PCSK9 is a member of the subtilisin serine protease family with an important role in lipoprotein metabolism. Mutation in the PCSK9 gene is associated with autosomal dominant hypercholesterolemia which is characterized by an increase in LDL cholesterol levels.