PCSK9 encodes a proprotein convertase belonging to the proteinase K subfamily of the secretory subtilase family. The encoded protein is synthesized as a soluble zymogen that undergoes autocatalytic intramolecular processing in the endoplasmic reticulum. The protein may function as a proprotein convertase. This protein plays a role in cholesterol homeostasis and may have a role in the differentiation of cortical neurons. Mutations in this gene have been associated with a third form of autosomal dominant familial hypercholesterolemia (HCHOLA3).