– 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. PCSK9 also plays a role in the neural development.