proprotein convertase subtilisin/kexin type 9, C-terminal cysteine-rich domain (CRD)PCSK9 post-translationally regulates hepatic low-density lipoprotein receptors (LDLRs) by binding to LDLRs on the cell surface, leading to their degradation. Other known PSCK9 targets include very-low-density lipoprotein receptor (VLDLR), apoE receptor2, lipoprotein receptor-related protein 1, etc. This PCSK9 C-terminal CRD may play an analogous role to the P (processing) domains of Furin and Kex2 (i.e. be required for the correct functioning/folding of the protein). Structural similarity has been noted between PCSK9 C-terminal CRD and the resistin homotrimer. This alignment model represents a three-fold repeat.