title: Identification of surface residues on Niemann-Pick C2 essential for hydrophobic handoff of cholesterol to NPC1 in lysosomes.
abstract: Water-soluble Niemann-Pick C2 (NPC2) and membrane-bound NPC1 are cholesterol-binding lysosomal proteins required for export of lipoprotein-derived cholesterol from lysosomes. The binding site in NPC1 is located in its N-terminal domain (NTD), which projects into the lysosomal lumen. Here we perform alanine-scanning mutagenesis to identify residues in NPC2 that are essential for transfer of cholesterol to NPC1(NTD). Transfer requires three residues that form a patch on the surface of NPC2. We previously identified a patch of residues on the surface of NPC1(NTD) that are required for transfer. We present a model in which these two surface patches on NPC2 and NPC1(NTD) interact, thereby opening an entry pore on NPC1(NTD) and allowing cholesterol to transfer without passing through the water phase. We refer to this transfer as a hydrophobic handoff and hypothesize that this handoff is essential for cholesterol export from lysosomes.
authors.affiliation: Department of Molecular Genetics, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Wang
authors.forename: Massoud
authors.initials: M
authors.lastname: Motamed
authors.forename: Rodney E
authors.initials: RE
authors.lastname: Infante
authors.forename: Lina
authors.initials: L
authors.lastname: Abi-Mosleh
authors.forename: Hyock Joo
authors.initials: HJ
authors.lastname: Kwon
authors.forename: Michael S
authors.initials: MS
authors.lastname: Brown
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Goldstein
mesh_terms: D000409:Alanine / Q000737:chemistry / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D016466:CHO Cells; D002352:Carrier Proteins / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D047908:Intracellular Signaling Peptides and Proteins; D008247:Lysosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D016296:Mutagenesis; D000077296:Niemann-Pick C1 Protein; D017434:Protein Structure, Tertiary; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; C104585:NPC2 protein, human; D000077296:Niemann-Pick C1 Protein; D033921:Vesicular Transport Proteins; D002784:Cholesterol; D000409:Alanine