Structural Basis of Low-pH-Dependent Lysosomal Cholesterol Egress by NPC1 and NPC2

Cell. 2020 Jul 9;182(1):98-111.e18. doi: 10.1016/j.cell.2020.05.020. Epub 2020 Jun 15.


Lysosomal cholesterol egress requires two proteins, NPC1 and NPC2, whose defects are responsible for Niemann-Pick disease type C (NPC). Here, we present systematic structural characterizations that reveal the molecular basis for low-pH-dependent cholesterol delivery from NPC2 to the transmembrane (TM) domain of NPC1. At pH 8.0, similar structures of NPC1 were obtained in nanodiscs and in detergent at resolutions of 3.6 Å and 3.0 Å, respectively. A tunnel connecting the N-terminal domain (NTD) and the transmembrane sterol-sensing domain (SSD) was unveiled. At pH 5.5, the NTD exhibits two conformations, suggesting the motion for cholesterol delivery to the tunnel. A putative cholesterol molecule is found at the membrane boundary of the tunnel, and TM2 moves toward formation of a surface pocket on the SSD. Finally, the structure of the NPC1-NPC2 complex at 4.0 Å resolution was obtained at pH 5.5, elucidating the molecular basis for cholesterol handoff from NPC2 to NPC1(NTD).

Keywords: NPC1; NPC2; Niemann-Pick disease type C; cholesterol transport; cryo-EM; lysosomal cholesterol egress; structural biology.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Line
  • Cholesterol / metabolism*
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Hydrogen-Ion Concentration
  • Intracellular Signaling Peptides and Proteins / chemistry*
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Lysosomes / metabolism*
  • Models, Molecular
  • Nanoparticles / chemistry
  • Nanoparticles / ultrastructure
  • Niemann-Pick C1 Protein
  • Protein Domains
  • Structural Homology, Protein
  • Structure-Activity Relationship
  • Vesicular Transport Proteins / chemistry*
  • Vesicular Transport Proteins / metabolism*


  • Intracellular Signaling Peptides and Proteins
  • NPC1 protein, human
  • NPC2 protein, human
  • Niemann-Pick C1 Protein
  • Vesicular Transport Proteins
  • Green Fluorescent Proteins
  • Cholesterol