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Lipid transporters and binding proteins; MsbA and NPC1
Author(s) -
Sharom Frances J.
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.408.1
Subject(s) - npc1 , endosome , flippase , atp binding cassette transporter , biochemistry , transport protein , chemistry , sterol regulatory element binding protein , microbiology and biotechnology , membrane protein , vesicle , biology , sterol , transporter , intracellular , membrane , cholesterol , gene , phospholipid , phosphatidylserine
Understanding the molecular mechanism of proteins that translocate or transfer lipids presents a special challenge. The bacterial ABC protein, MsbA, is a homodimeric “half‐transporter” of known structure, which is thought to act as an outwardly‐directed ATP‐driven flippase for lipid A and possibly some phospholipids. We have purified MsbA with high ATPase activity and established its binding affinity for putative substrates using fluorescence spectroscopic tools. Reconstituted MsbA displays a high level of flippase activity for certain phospholipids, providing an excellent opportunity to explore the mechanism of lipid translocation at the molecular level. Mutations in NPC1 cause Niemann‐Pick Type C disease, a fatal neurodegenerative condition characterized by accumulation of cholesterol and glycolipids in the late endosomes. NPC1 is a 190 kDa integral protein found in the late endosomal membrane. It is known to be a key player in intracellular cholesterol trafficking, but the nature of its substrates and its exact role remain enigmatic. Recent studies on purified NPC1 have shown that it binds several sterols, and the binding site has been localized to the N‐terminal luminal domain, which has been crystallized in sterol‐bound form. NPC1 may accept sterol from NPC2, a small soluble protein in the lumen of late endosomes, and transfer it to either the membrane, or an as yet unidentified cytoplasmic acceptor.