PCSK9, a member of the peptidase S8 family (enzymes that preferentially catalyze the hydrolysis of leucine residues at the N-terminus of peptides and proteins), reveals four major components in the pre-processed protein: the signal peptide ; the N-terminal prodomain; the catalytic domain; and the C-terminal domain.
PCSK9 is a member of the peptidase S8 family. Leucyl aminopeptidases (EC , leucine aminopeptidase, LAPs, leucyl peptidase, peptidase S, cytosol aminopeptidase, cathepsin III, L-leucine aminopeptidase, leucinaminopeptidase, leucinamide aminopeptidase, FTBL proteins, proteinates FTBL, aminopeptidase II, aminopeptidase III, aminopeptidase I) are enzymes that preferentially catalyze the hydrolysis of leucine residues at the N-terminus of peptides and proteins. The solved structure of PCSK9 reveals four major components in the pre-processed protein: the signal peptide (residues 1-30); the N-terminal prodomain (residues 31-152); the catalytic domain (residues 153-425); and the C-terminal domain (residues 426-692), which is further divided into three modules. 
