Niemann-Pick C1 protein (NPC1) is a late-endosomal membrane protein involved in trafficking of LDL-derived cholesterol, Niemann-Pick disease type C, and Ebola virus infection. NPC1 contains 13 transmembrane segments (TMs), five of which are thought to represent a “sterol-sensing domain” (SSD). Although present also in other key regulatory proteins of cholesterol biosynthesis, uptake, and signaling, the structure and mechanism of action of the SSD are unknown. Here we report a crystal structure of a large fragment of human NPC1 at 3.6 Å resolution, which reveals internal twofold pseudosymmetry along TM 2-13 and two structurally homologous domains that protrude 60 Å into the endosomal lumen. Strikingly, NPC1’s SSD forms a cavity that is accessible from both the luminal bilayer leaflet and the endosomal lumen; computational modeling suggests that this cavity is large enough to accommodate one cholesterol molecule.
Niemann-Pick is a rare, inherited disease that affects the body’s ability to metabolize fat (cholesterol and lipids) within cells. These cells malfunction and, over time, die. Niemann-Pick disease can affect the brain, nerves, liver, spleen, bone marrow and, in severe cases, lungs.
People with this condition experience symptoms related to progressive loss of function of nerves, the brain and other organs
This 3D print of Niemann Pick C is printed in full-color sandstone and colored by the protein’s hydrophobicity. Blue is are the hydrophilic regions of the protein, and red colors the hydrophobic regions. Since this is a membrane bound protein, visualizing its hydrophobicity allows us to visually identify the hydrophobic portion that spans the plasma membrane. Models are available in multiple sizes.