title: Multiple Surface Regions on the Niemann-Pick C2 Protein Facilitate Intracellular Cholesterol Transport.
abstract: The cholesterol storage disorder Niemann-Pick type C (NPC) disease is caused by defects in either of two late endosomal/lysosomal proteins, NPC1 and NPC2. NPC2 is a 16-kDa soluble protein that binds cholesterol in a 1:1 stoichiometry and can transfer cholesterol between membranes by a mechanism that involves protein-membrane interactions. To examine the structural basis of NPC2 function in cholesterol trafficking, a series of point mutations were generated across the surface of the protein. Several NPC2 mutants exhibited deficient sterol transport properties in a set of fluorescence-based assays. Notably, these mutants were also unable to promote egress of accumulated intracellular cholesterol from npc2(-/-) fibroblasts. The mutations mapped to several regions on the protein surface, suggesting that NPC2 can bind to more than one membrane simultaneously. Indeed, we have previously demonstrated that WT NPC2 promotes vesicle-vesicle interactions. These interactions were abrogated, however, by mutations causing defective sterol transfer properties. Molecular modeling shows that NPC2 is highly plastic, with several intense positively charged regions across the surface that could interact favorably with negatively charged membrane phospholipids. The point mutations generated in this study caused changes in NPC2 surface charge distribution with minimal conformational changes. The plasticity, coupled with membrane flexibility, probably allows for multiple cholesterol transfer routes. Thus, we hypothesize that, in part, NPC2 rapidly traffics cholesterol between closely appositioned membranes within the multilamellar interior of late endosomal/lysosomal proteins, ultimately effecting cholesterol egress from this compartment.
authors: Department of Nutritional Sciences and Rutgers Center for Lipid Research and.
authors: Leslie A
authors: LA
authors: McCauliff
authors: Department of Nutritional Sciences and Rutgers Center for Lipid Research and.
authors: Zhi
authors: Z
authors: Xu
authors: Department of Nutritional Sciences and Rutgers Center for Lipid Research and.
authors: Ran
authors: R
authors: Li
authors: Department of Nutritional Sciences and Rutgers Center for Lipid Research and.
authors: Sarala
authors: S
authors: Kodukula
authors: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina 27710.
authors: Dennis C
authors: DC
authors: Ko
authors: Department of Developmental Biology and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305.
authors: Matthew P
authors: MP
authors: Scott
authors: Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey 08901.
authors: Peter C
authors: PC
authors: Kahn
authors: Department of Nutritional Sciences and Rutgers Center for Lipid Research and. Electronic address: storch@aesop.rutgers.edu.
authors: Judith
authors: J
authors: Storch
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002784:Cholesterol / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008563:Membrane Lipids / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D011487:Protein Conformation; D055672:Static Electricity; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; D008563:Membrane Lipids; D050505:Mutant Proteins; C104585:NPC2 protein, human; D033921:Vesicular Transport Proteins; D002784:Cholesterol
keywords: NPC2; Niemann-Pick C2; cholesterol; cholesterol-binding protein; lipid transport; lipid-protein interaction; lysosomal storage disease; membrane contact sites; protein conformation