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Myelin Proteins in Reverse Micelles: Tight Lipid Association Required for Insertion of the Folch‐Pi Proteolipid into a Membrane‐Mimetic System
Author(s) -
Vacher Monique,
Waks Marcel,
Nicot Claude
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb10905.x
Subject(s) - micelle , chemistry , myelin , proteolipid protein 1 , solubility , myelin proteolipid protein , chromatography , integral membrane protein , lipid bilayer , membrane , biochemistry , membrane protein , aqueous solution , biophysics , myelin basic protein , organic chemistry , biology , central nervous system , neuroscience
The solubility and reactivity of the Folch‐Pi proteolipid from bovine CNS have been studied in reverse micelles of sodium bis(2‐ethylhexyl)sulfosuccinate, isooctane, and water. Such a membrane‐mimetic system resembles the aqueous spaces of the native myelin sheath in terms of its physicochemical properties. Although the proteolipid is completely insoluble in water, it can be inserted into the water‐containing micellar system. In contrast, the lipid‐depleted protein failed to be incorporated into these organized assemblies. The lipid requirements for insertion of the proteolipid were studied, therefore, after delipidation by several precipitations with isooctane, a nondenaturing solvent. Novel extraction procedures and quantitative analyses by HPLC of the protein‐bound lipids revealed the persistence of a lipidprotein complex (6 ± 1 mol of lipid/mol of protein) displaying optimal micellar solubilization. Competition experiments carried out with brain lipids provide evidence for a preference of the myelin protein for sulfatide, phosphatidylinositol, and phosphatidylserine, in that order. The resulting proteolipid, although differing in relative composition, showed good solubility in the membrane‐mimetic system. In contrast, reconstitution experiments carried out with the lipid‐depleted protein resulted in weak lipid binding and poor micellar incorporation. These results suggest that the tightly bound acidic lipids may stabilize a protein conformation required for insertion into the micellar system.