Human Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) is a secretory subtilase belonging to the proteinase K subfamily. PCSK9 is synthesized as a soluble zymogen that undergoes autocatalytic intramolecular processing in the ER , the pro domain and mature chain secrete together through noncovalent interactions. PCSK9 binds with low-density lipoprotein receptor (LDLR) and plays a major regulatory role in cholesterol homeostasis. Inhibition of PCSK9 function by preventing PCSK9/LDLR interaction is currently being explored as a means of lowering cholesterol levels. PCSK9 also binds to apolipoprotein receptor 2 (ApoER2), and play a role in the neural development.