Cholesterol Transport in Wild-Type NPC1 and P691S: Molecular Dynamics Simulations Reveal Changes in Dynamical...

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Niemann-Pick C1 (NPC1) protein is central to NPC disease, a fatal lysosomal lipid storage disorder.
• The sterol-sensing domain (SSD) of NPC1 is implicated in cholesterol binding and trafficking, but its precise role remains unclear.
• A cryo-EM structure identified an itraconazole binding site (IBS) within the NPC1 SSD.

Purpose of the Study:

• To investigate the molecular dynamics of cholesterol binding and trafficking in wild-type (WT) NPC1 and the P691S mutant.
• To elucidate the structural basis for altered cholesterol dynamics in the P691S mutant compared to WT NPC1.

Main Methods:

• Construction of molecular models for cholesterol-bound WT and P691S NPC1.
• Performance of molecular dynamics (MD) simulations on these models.
• Analysis of structural features within the itraconazole binding site (IBS) and their impact on protein dynamics.

Main Results:

• In WT NPC1, cholesterol exhibited lateral migration towards the lipid bilayer.
• In the P691S mutant, cholesterol was observed to migrate away from the SSD towards the N-terminal domain through a newly identified tunnel.
• The P691S mutation introduces a unique hydrogen bond network involving Ser691, absent in WT NPC1, altering protein dynamics.

Conclusions:

• The P691S mutation significantly alters cholesterol dynamics within NPC1 by creating a pathway for its release from the SSD.
• The introduced hydrogen bond network at residue 691 is responsible for the altered dynamics and disrupted cholesterol trafficking in the P691S mutant.
• These findings provide a molecular explanation for experimental observations of impaired cholesterol trafficking in NPC disease.