Functional analysis of sites within PCSK9 responsible for hypercholesterolemia

Area of Science:

• Biochemistry
• Genetics
• Molecular Biology

Background:

• Proprotein convertase subtilisin/kexin type 9 (PCSK9) mutations are linked to familial hypercholesterolemia.
• PCSK9 binds the LDL receptor (LDLR), promoting its degradation and reducing LDL uptake.
• Certain PCSK9 mutations, like S127R and D374Y, are known to be more potent than wild-type PCSK9 in decreasing LDL uptake.

Purpose of the Study:

• To investigate the mechanistic basis by which mutations at PCSK9 residues Ser127 and Asp374 influence PCSK9 function.
• To understand how specific amino acid substitutions affect PCSK9's interaction with the LDLR and its overall efficacy.

Main Methods:

• Limited vertical scanning mutagenesis was performed at the Ser127 and Asp374 sites of PCSK9.
• Exogenous addition of wild-type and mutant PCSK9 proteins to cells to assess LDL uptake.
• In vitro assays to evaluate the interaction potency of D374 mutants with LDLR.
• Computational modeling of PCSK9 mutations at Ser127 and Asp374.

Main Results:

• Mutations S127R and S127K in PCSK9 demonstrated increased potency in reducing LDL uptake compared to wild-type.
• All tested D374 mutants exhibited enhanced potency in reducing LDL uptake when added exogenously.
• The potency of D374 mutants in lowering LDL uptake correlated with their in vitro binding affinity to LDLR.
• A combination of S127R and D374Y mutations showed an additive effect in reducing LDL uptake.

Conclusions:

• Mutations at Ser127 and Asp374 residues modulate PCSK9's regulation of LDLR function through distinct mechanisms.
• Mutations enhancing PCSK9 function may stabilize the protein (Ser127), while others may destabilize it (Asp374).
• These findings provide insights into the molecular mechanisms underlying PCSK9-related hypercholesterolemia and potential therapeutic targets.