NPC2 facilitates bidirectional transfer of cholesterol between NPC1 and lipid bilayers, a step in cholesterol egress from lysosomes.
Egress of lipoprotein-derived cholesterol from lysosomes requires two lysosomal proteins, polytopic membrane-bound Niemann-Pick C1 (NPC1) and soluble Niemann-Pick C2 (NPC2). The reason for this dual requirement is unknown. Previously, we showed that the soluble luminal N-terminal domain (NTD) of NPC1 (amino acids 25-264) binds cholesterol. This NTD is designated NPC1(NTD). We and others showed that soluble NPC2 also binds cholesterol. Here, we establish an in vitro assay to measure transfer of [(3)H]cholesterol between these two proteins and phosphatidylcholine liposomes. Whereas NPC2 rapidly donates or accepts cholesterol from liposomes, NPC1(NTD) acts much more slowly. Bidirectional transfer of cholesterol between NPC1(NTD) and liposomes is accelerated >100-fold by NPC2. A naturally occurring human mutant of NPC2 (Pro120Ser) fails to bind cholesterol and fails to stimulate cholesterol transfer from NPC1(NTD) to liposomes. NPC2 may be essential to deliver or remove cholesterol from NPC1, an interaction that links both proteins to the cholesterol egress process from lysosomes. These findings may explain how mutations in either protein can produce a similar clinical phenotype.
Infante
Rodney E
RE
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046, USA.
Wang
Michael L
ML
Radhakrishnan
Arun
A
Kwon
Hyock Joo
HJ
Brown
Michael S
MS
Goldstein
Joseph L
JL
D002352:Carrier Proteins / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism*; D008074:Lipoproteins / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008954:Models, Biological; D000077296:Niemann-Pick C1 Protein; D009542:Niemann-Pick Diseases / Q000378:metabolism; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D008051:Lipid Bilayers; D008074:Lipoproteins; D008081:Liposomes; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; C104585:NPC2 protein, human; D000077296:Niemann-Pick C1 Protein; D033921:Vesicular Transport Proteins; C030104:lipoprotein cholesterol; D002784:Cholesterol
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