Niemann-Pick disease type C (NPC) is associated with mutations in NPC1 and NPC2, whose gene products are key players in the endosomal/lysosomal egress of low-density lipoprotein-derived cholesterol. NPC1 is also the intracellular receptor for Ebola virus (EBOV). Here, we present a 4.4 Å structure of full-length human NPC1 and a low-resolution reconstruction of NPC1 in complex with the cleaved glycoprotein (GPcl) of EBOV, both determined by single-particle electron cryomicroscopy. NPC1 contains 13 transmembrane segments (TMs) and three distinct lumenal domains A (also designated NTD), C, and I. TMs 2-13 exhibit a typical resistance-nodulation-cell division fold, among which TMs 3-7 constitute the sterol-sensing domain conserved in several proteins involved in cholesterol metabolism and signaling. A trimeric EBOV-GPcl binds to one NPC1 monomer through the domain C. Our structural and biochemical characterizations provide an important framework for mechanistic understanding of NPC1-mediated intracellular cholesterol trafficking and Ebola virus infection.

ABCA1, an ATP-binding cassette (ABC) subfamily A exporter, mediates the cellular efflux of phospholipids and cholesterol to the extracellular acceptor apolipoprotein A-I (apoA-I) for generation of nascent high-density lipoprotein (HDL). Mutations of human ABCA1 are associated with Tangier disease and familial HDL deficiency. Here, we report the cryo-EM structure of human ABCA1 with nominal resolutions of 4.1 Å for the overall structure and 3.9 Å for the massive extracellular domain. The nucleotide-binding domains (NBDs) display a nucleotide-free state, while the two transmembrane domains (TMDs) contact each other through a narrow interface in the intracellular leaflet of the membrane. In addition to TMDs and NBDs, two extracellular domains of ABCA1 enclose an elongated hydrophobic tunnel. Structural mapping of dozens of disease-related mutations allows potential interpretation of their diverse pathogenic mechanisms. Structural-based analysis suggests a plausible "lateral access" mechanism for ABCA1-mediated lipid export that may be distinct from the conventional alternating-access paradigm.

The Hedgehog (Hh) pathway involved in development and regeneration is activated by the extracellular binding of Hh to the membrane receptor Patched (Ptch). We report the structures of human Ptch1 alone and in complex with the N-terminal domain of human Sonic hedgehog (ShhN) at resolutions of 3.9 and 3.6 angstroms, respectively, as determined by cryo-electron microscopy. Ptch1 comprises two interacting extracellular domains, ECD1 and ECD2, and 12 transmembrane segments (TMs), with TMs 2 to 6 constituting the sterol-sensing domain (SSD). Two steroid-shaped densities are resolved in both structures, one enclosed by ECD1/2 and the other in the membrane-facing cavity of the SSD. Structure-guided mutational analysis shows that interaction between ShhN and Ptch1 is steroid-dependent. The structure of a steroid binding-deficient Ptch1 mutant displays pronounced conformational rearrangements.