The intramembranous domains of lipophilin in phosphatidylcholine vesicles are similar to those in the myelin membrane

doi:10.1016/0005-2736(86)90487-6

Biochimica et Biophysica Acta (BBA) - Biomembranes

Volume 862, Issue 1, 6 November 1986, Pages 223-226

https://doi.org/10.1016/0005-2736(86)90487-6 Get rights and content

Abstract

A membrane-permeable photolabel 3-(trifluoromethyl)-3-(m-[¹²⁵I]iodophenyl)diazirine (¹²⁵I-TID) has been used to label lipophilin in normal human myelin and after incorporation of purified lipophilin into phosphatidylcholine (PC) vesicles. The labelled protein was isolated and the specific activities for lipophilin from myelin and from PC vesicles was found to be 1.2·10¹¹ and 1.5·10¹¹ cpm/mol, respectively. The chromatographic profiles of tryptic peptides were similar in both cases and the specific activities of the C-terminal intramembranous fragments (residues 205–268) the same. We concluded that the organization of lipophilin in PC vesicles was similar to its organization in myelin and that the PC-vesicle system represents a good system in which to study the orientation and interaction of lipophilin with lipids.

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Cited by (7)

Human proteolipid protein (PLP) mediates winding and adhesion of phospholipid membranes but prevents their fusion
1998, Biochimica et Biophysica Acta - Biomembranes
Proteolipid protein (PLP or lipophilin) is a highly conserved, strongly hydrophobic, integral membrane protein, and is the major protein component of central nervous system myelin. Although PLP has been implicated in many functions, its in vivo role is still uncertain. Here, we report the investigation of PLP’s putative adhesive function using purified PLP and reconstituted phospholipid vesicles made of either 100% phosphatidylcholine (PC), or a mixture of 92% PC and 8% phosphatidylserine (PS), by weight. PLP-induced changes in the phospholipid bilayer surfaces were directly examined by transmission electron microscopy. We found that upon the introduction of PLP, larger lipid vesicles became smaller and unilamellar. At the PLP:lipid molar ratio of 1:20, vesicle membranes rolled onto themselves forming ‘croissant’-like structures that subsequently adhered to each other. The phenomena of PLP-induced bilayer rolling and adhesion were dependent on the concentration of PLP and the period of incubation, but were independent of the presence of calcium and types of phospholipids (PC or PC:PS). Furthermore, the presence of PLP in the lipid bilayers prevented the fusion of membranes. These findings show that PLP can induce membrane ‘winding’ while preventing the fusion of adjacent lipid bilayers. Hence, our data provide direct evidence for PLP’s suspected function of membrane adhesion, and also suggest that PLP could potentially play a role in the formation of the myelin sheath.
Comparative study of myelin proteolipid apoprotein solvation by multilayer membranes of synthetic DPPC and biological lipid extract from bovine brain. An FT-IR investigation
1989, Biochimie
The interaction between the aqueous form of the myelin proteolipid apoprotein (PLA) and model membranes prepared with either synthetic dipalmitoylphosphatidyl choline (DPPC) or biological lipids extracted from bovine brain (BE) has been investigated by Fourier-Transform IR spectroscopy.
IR spectra obtained with lyophilized samples of PLA demonstrated 2 main peaks (amide I and amide II) culminating at 1656 cm⁻¹ and 1545 cm⁻¹, which we assigned to helical conformation. When PLA was solvated in DPPC or BE membranes, both the amide I and amide II features remained located at 1655 cm⁻¹ and 1545 cm⁻¹, although their half-width significantly decreased, demonstrating that the lipid environment favoured α helix structures. However differences between both mixtures were detected by measuring the amide I and amide II half-widths as a function of the L:P molar ratio.
Moreover, analysis of the 1545/1515 peak intensity ratio brought evidence of different localization and/or molecular arrangement of the protein segments containing tyrosine residues, depending on the lipid composition of the membrane. According to previously published models, these data suggest that recombinants prepared with PLA and BE multilayers better mimic the biological membrane than do DPPC-PLA mixtures.
The secondary structure of a membrane-embedded peptide from the carboxy terminus of lipophilin as revealed by circular dichorism
1988, Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Several intramembranous peptides have been isolated from the major myelin proteolipid protein (lipophilin) isolated from normal human myelin membrane after labelling the protein with a membrane-permeable photolabel, $3-(trifluoromethyl)-3-(m-[^{125} I] iodophenyl)diazirine$ . Peptide T-3, comprising residues 205–268, represents the C-terminal portion of the protein. Reconstitution of peptide T-3 into lipid vesicles prepared from egg phosphatidylcholine (PC) or into lysoPC micelles yielded visually transparent preparations, free of scattering artifacts, which were used for circular dichroism studies to assess the extent of secondary structure in the peptide. Peptide T-3 had a high degree of α-helix in various environments. In aqueous environment, the secondary structure was 45% α-helix, 33% β-structure and 9% β-turns. Transfer of the peptide to PC vesicles or lysoPC micelles increased the proportion of α-helix and decreased that of β-structure. In PC vesicles, the α-helical content was 80% with little or no β-structure. Small amounts of other structures such as β-turns and unordered structures were also present. The partitioning of this C-terminal section of lipophilin into membranes may have an important role initiating and/or stabilizing the native conformation of lipophilin in the myelin membrane.
Myelin proteolipid protein-induced aggregation of lipid vesicles: Efficacy of the various molecular species
2002, Neurochemical Research
Chemical deacylation reduces the adhesive properties of proteolipid protein and leads to decompaction of the myelin sheath
2001, Journal of Neurochemistry
A Hydrophobic Inhibitor of the Nicotinic Acetylcholine Receptor Acts on the Resting State
1994, Biochemistry

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BBA reportThe intramembranous domains of lipophilin in phosphatidylcholine vesicles are similar to those in the myelin membrane

Abstract

Biochemistry

Biochim. Biophys. Acta

BBA report
The intramembranous domains of lipophilin in phosphatidylcholine vesicles are similar to those in the myelin membrane