Fig. 1

There is a signal peptide (amino acids 1 to 30), a prodomain (amino acids 31 to 152), a catalytic domain (amino acids 153 to 452), and a C-terminal domain (amino acids 453 to 692) that make up the mature form of PCSK9. The signal peptide breaks apart when it gets to the endoplasmic reticulum (ER), and the PCSK9 zymogen is automatically made between Gln152 and Ser153 (serine-isoleucine-proline (SIP)/valine-phenylalanine-alanine-glutamine (VFAQ)152). Furin enzymes turn off the adult version of PCSK9, which is about 60 kDa long (aa 153 to 692). This makes it shorter, to 55 kDa. The orange boxed area shows the signal peptide (SP), the yellow boxed area shows the prodomain, the green boxed area shows the catalytic domain, and the blue boxed area shows the C-terminal domain [22]