Abstract 19863: Proprotein Convertase Subtilisin/Kexin Type 9 May Associate With Lipoproteins Through Lipid Interactions
Background: Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) is a secreted plasma protein that binds and promotes degradation of cell-surface low density lipoprotein (LDL) receptors in the liver, impairing clearance of LDL from the blood. PCSK9 inhibition has become an important therapeutic avenue for hypercholesterolemia. PCSK9 also associates with LDL particles, and is inhibited by LDL in cell culture. This interaction holds implications for therapeutic development. An N-terminal region of the PCSK9 prodomain is required for PCSK9-LDL binding, and is also auto-inhibitory to the LDL receptor degrading function of PCSK9. Thus, this N-terminal region may play an allosteric role in regulating PCSK9 activity. PCSK9 polymorphisms such as the loss-of-function R46L or the gain-of-function S127R are also located in or near this N-terminal region.
Hypothesis: Specific residues within the PCSK9 prodomain N-terminal regulate the PCSK9-LDL interaction.
Methods: Targeted residues in the N-terminal region were altered by mutagenesis. Subsequent LDL binding in-vitro was determined by separation of LDL-bound and non-bound PCSK9 by gradient ultracentrifugation. Structural studies using circular dichroism (CD) assessed secondary structure of an N-terminal region peptide in hydrophobic versus aqueous conditions.
Results: LDL binding data from various targeted PCSK9 mutations suggest that the N-terminal region of PCSK9 could be involved in a lipid-induced random coil-to-helix transition, forming an amphipathic helix that could aid PCSK9-LDL binding through a lipid interaction. Preliminary CD data indicates that a coil-to-helix transition indeed occurs in a hydrophobic environment. This transition appears to be stronger for the R46L polymorphism. As well, familial hypercholesterolemia-associated PCSK9 variants S127R, D129G and L108R show loss of LDL-binding in-vitro.
Conclusions: PCSK9 activity in circulation may be regulated by LDL association, aided by lipid interactions. As well, the ability of PCSK9 to bind LDL may play a role in the mechanism of action of gain-of-function PCSK9 variants associated with familial hypercholesterolemia.
Author Disclosures: S.K. Sarkar: None. N. Goto: None. T.A. Lagace: None.
- © 2016 by American Heart Association, Inc.