| Budget Amount *help |
¥7,000,000 (Direct Cost: ¥7,000,000)
Fiscal Year 1997: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1996: ¥5,700,000 (Direct Cost: ¥5,700,000)
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| Research Abstract |
Caveolae are non-clathrin-coated surface invaginations present in many cell types and function as a device to trap glycolipids, cholesterol, and other proteins for potocytosis, endocytosis, transcytosis, and intracellular signal transductions. Caveolin (caveolin-1) is a 21-24 kDa integral membrane protein, which is localized to both caveolae and trans-Golgi derived exocytic vesicles. To investigate the possible lipid interactions of caveolin, we reconstituted Esherichia coil-expressed caveolin into proteoliposomes with various lipid compositions and found that the protein was incorporated into DOPC/cholesterol proteoliposomes only when >30 mole % cholesterol was present in the lipid mixture. We also demonstrated that the protein bound cholesterol specifically. A number of proteins are known to interact with cholesterol, but to our knowledge caveolin is the first "membrane protein" that binds cholesterol. The organizing mechanism for the complexes of caveolin and cholesterol molecules has not yet been elucidated. The finding that cholesterol remained bound to the protein was completely unexpected since the final purification step of dog lung caveolin, which isolated from dog lung using biochemically, was sedimentation through a sucrose gradient containing 0.2% SDS, which should have removed associated lipids. Therefore, the binding of cholesterol to caveolin is markedly stable, suggesting lipid-protein interactions with unusual characteristics. This finding indicates that the protein plays a specific role in membrane microdomain (caveolar-related domains) formation and intracellular cholesterol trafficking.
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