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Abstract
This review is a personal memoir of the history of proteolipids and is limited to aspects of the field with which the author has been involved in one way or another. The discovery of proteolipids was a serendipitous observation made in the course of the study of sulfatides. Initial focus was on the chemical characterization of brain proteolipids, their behavior under different conditions and their identification as the major protein of CNS myelin. The sequence of PLP was obtained using solid phase protein sequencing techniques. This, in turn, made possible a new era in which biochemical, cellular and molecular approaches could be applied to address new questions about PLP. Identification of genetic defects in the PLP molecule and its regulation has contributed to understanding myelin biology. Studies of the encephalitogenic activity of PLP in animal models have influenced the views of inflammatory processes in multiple sclerosis. Despite remarkable progress, much remains to be learned about the structure and function of PLP.
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Affiliation(s)
- M B Lees
- Biomedical Sciences Division, E.K. Shriver Center, Waltham, MA 02254, USA
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2
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Bizzozero OA, Good LK, Evans JE. Cysteine-108 is an acylation site in myelin proteolipid protein. Biochem Biophys Res Commun 1990; 170:375-82. [PMID: 1695508 DOI: 10.1016/0006-291x(90)91284-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Myelin proteolipid protein (PLP) contains covalently bound long-chain fatty acids. A large proportion of these acyl moieties are bound in thioester linkages, as demonstrated by alkylation of newly formed SH groups upon deacylation. To identify the Cys residue(s) involved in the thioester linkage(s), reduced and carboxyamidomethylated proteolipid protein was labeled with [14C]iodoacetamide upon deacylation with neutral hydroxylamine. The labeled protein was digested with trypsin or pepsin, and peptides analyzed by RP-HPLC. Identification of the isolated radioactive peptides by amino acid analysis, peptide sequencing and/or fast-atom bombardment-mass spectrometry revealed that Cys108 in the bovine PLP sequence is an acylated site. The sequence surrounding the palmitoylation site in the myelin PLP is strikingly similar to that found in rhodopsin. Furthermore, as in rhodopsin and other members of the G protein-coupled receptor family, this Cys residue is located within a hydrophilic, basic, and possibly cytoplasmic, domain.
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Affiliation(s)
- O A Bizzozero
- Biochemistry Dept., E. K. Shriver Center, Waltham, MA 02254
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Shaw SY, Laursen RA, Lees MB. Identification of thiol groups and a disulfide crosslink site in bovine myelin proteolipid protein. FEBS Lett 1989; 250:306-10. [PMID: 2473918 DOI: 10.1016/0014-5793(89)80744-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The existence of disulfide crosslinks limits the number of possible folded structures a protein can assume. Thus localization of disulfide and thiol groups is a key to understanding the conformation and orientation of myelin proteolipid protein (PLP) in the myelin membrane. [14C]Carboxamidomethylated PLP was fragmented with chymotrypsin, and the resulting mixture was partially separated by reversed-phase HPLC. Purified 14C-labeled peptides and a disulfide containing peptide were characterized by amino acid analysis. These experiments showed that Cys-32 and Cys-34 are free thiols, and are presumably on the interior of the cell or within the membrane bilayer, and that Cys-200 and Cys-219 are joined by a disulfide bond, and are probably located on the extracellular face of the membrane. Sequence analysis experiments indicate that Cys-5, Cys-6 and Cys-9 are linked by disulfides, probably to other parts of the protein on the extracellular face of the membrane.
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Affiliation(s)
- S Y Shaw
- Department of Chemistry, Boston University, MA 02215
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4
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Lux B, Helynck G, Trifilieff E, Luu B, Gerard D. Intrinsic fluorescence of a non-myelin apoproteolipid and evidence for the existence of conformational flexibility. Biophys Chem 1984; 19:345-53. [PMID: 17005146 DOI: 10.1016/0301-4622(84)87017-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/1983] [Revised: 01/10/1984] [Accepted: 01/24/1984] [Indexed: 10/18/2022]
Abstract
An extremely hydrophobic protein (Mr = 16000), which in its native form is only soluble in organic solvents and which differs from the myelin proteolipid (Mr = 24000), was purified to homogeneity. Intrinsic fluorescence studies on this apoproteolipid have revealed a large conformational flexibility. In the water-soluble form the emitting residues appear to be buried in a hydrophobic core while in organic solvents they are exposed to the external medium. Structural changes depending on the organic solvent are also observed. The emission characteristics of reconstituted proteoliposomes may be due to the formation of a membrane-linked complex between several proteolipid monomers.
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Affiliation(s)
- B Lux
- Laboratoire de Biophysique, ERA CNRS 551, UER des Sciences Pharmaceutiques, Université Louis Pasteur, B.P. 10, 67048 Strasbourg Cedex, France
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Laursen RA, Samiullah M, Lees MB. The structure of bovine brain myelin proteolipid and its organization in myelin. Proc Natl Acad Sci U S A 1984; 81:2912-6. [PMID: 6201866 PMCID: PMC345183 DOI: 10.1073/pnas.81.9.2912] [Citation(s) in RCA: 105] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
A model, based on amino acid sequence data, is proposed for the organization of the myelin proteolipid in myelin membrane. The model has three distinctive features: three trans-membrane segments that traverse the lipid bilayer, two cis-membrane domains that enter and exit the same side of the membrane, and a highly charged segment resembling myelin basic protein on the cytoplasmic side of the membrane. It is proposed that the cis-membrane domain(s) can promote the formation and stabilization of the multilamellar myelin structure by hydrophobic interaction with the apposite bilayer across the extracellular space.
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Lees MB, Chao BH, Lin LF, Samiullah M, Laursen RA. Amino acid sequence of bovine white matter proteolipid. Arch Biochem Biophys 1983; 226:643-56. [PMID: 6195969 DOI: 10.1016/0003-9861(83)90334-x] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The sequence of the bovine white matter proteolipid has been studied by a combination of proteolytic digestion and chemical cleavage at tryptophan residues. Alignment of peptides obtained by digestion with trypsin, chymotrypsin, clostripain, and Staphylococcus aureus protease gave the sequence of 52 residues at the amino terminus, 96 residues at the carboxyl terminus, and several additional segments. Peptides obtained by treatment of the protein with 2-(2-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine confirmed the alignment and extended the sequence. This information, combined with that of other investigators, permits us to propose the primary structure for the entire protein. On the basis of the sequence determination, the molecular weight of the proteolipid protein is 29,869.
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Stoffel W, Hillen H, Schröder W, Deutzmann R. The primary structure of bovine brain myelin lipophilin (proteolipid apoprotein). HOPPE-SEYLER'S ZEITSCHRIFT FUR PHYSIOLOGISCHE CHEMIE 1983; 364:1455-66. [PMID: 6642431 DOI: 10.1515/bchm2.1983.364.2.1455] [Citation(s) in RCA: 111] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The amino-acid sequence of bovine myelin lipophilin (proteolipid apoprotein, Folch-protein) has been completed. Lipophilin is a 276 amino acid residues containing, extremely hydrophobic membrane protein with molecular mass 30,000 Da. The sequence determination was based on automated Edman degradation of four tryptophan and four cyanogen bromide fragments and of proteolytic peptides of complete lipophilin as well as the fragments obtained by chemical cleavage. Four additional sequences were determined which led to the completion of the primary structure. Lipophilin is esterified at threonine-198 by long chain fatty acids (palmitic, stearic and oleic acid). The attachment site has been established at the same threonine residue in three different peptides isolated from thermolysinolytic, papainolytic and chymotrypsinolytic hydrolysates. This threonine residue is part of a hydrophilic segment of lipophilin. The covalent fatty acyl bond is being discussed together with important structural and functional properties of this membrane protein which can be derived from sequence information. New separation and purification methods of hydrophobic and hydrophilic polypeptides for this sequence determination (fractional solubilization, silica gel exclusion, high-performance liquid chromatography) had to be elaborated as indispensable tools. They are generally applicable to the structural analysis of hydrophobic membrane proteins. Four long (26, 29, 40 and 36 residues) and one medium long (12 residues) hydrophobic segments are separated by four predominantly positively and one negatively charged hydrophilic segments. On the basis of structural data a model for the membrane integration of lipophilin is proposed.
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Lees MB, Chao BH, Laursen RA, L'Italien JJ. A hydrophobic tryptic peptide from bovine white matter proteolipid. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 702:117-24. [PMID: 7066340 DOI: 10.1016/0167-4838(82)90034-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
A hydrophobic, chloroform-soluble tryptic peptide with a molecular weight of approximately 4000 has been purified from the bovine white matter proteolipid protein. Its primary structure was obtained by a combination of solid-phase Edman degradation and mass spectrometry. A major part of the tryptic peptide appears to be inaccessible to the action of proteolytic enzymes. The peptide spans the three cyanogen bromide peptides located by Jollès et al. (Biochem. Biophys. Res. Commun. (1979) 87, 619--626) at the COOH-terminal region of the intact protein. Secondary structure calculations for this region indicate a segregation into discrete domains, with most of the tryptic peptide corresponding to a highly ordered, hydrophobic domain; an equal probability for alpha-helical or beta-structure is predicted for this region.
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Lees MB, Macklin WB, Chao BH. A study of elastase peptides from bovine white matter proteolipid. Neurochem Res 1981; 6:1091-104. [PMID: 6917041 DOI: 10.1007/bf00964415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Bovine white matter proteolipid has been digested with elastase in the presence of deoxycholate. After acidification, the digest was separated into an acid-soluble and an acid-insoluble fraction. The acid-insoluble fraction was enriched in nonpolar amino acids and, by a combination of solvent fractionation and chromatography, a fraction was obtained which consisted of a mixture of two peptides with a molecular weight of approximately 4000 daltons. The acid-soluble peptides were separated by molecular sieve, ion exchange and high performance liquid chromatography (HPLC) in the reverse phase mode. The purified peptides were smaller than expected on the basis of their elution position from a molecular sieve column, suggesting they were in an aggregated state during the initial chromatography. Reverse phase HPLC was shown to be useful for fingerprinting these peptide mixtures. The data demonstrate the difficulties associated with the study of this proteolipid and emphasize the tendency of both the protein and the peptides derived from it to aggregate.
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Sakura JD. Physical properties of bovine white matter proteolipid apoprotein-sodium dodecyl sulfate complexes. J Neurosci Res 1981; 6:689-700. [PMID: 7334530 DOI: 10.1002/jnr.490060602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The interaction of bovine white matter proteolipid apoproteins with sodium dodecyl sulfate (SDS) was studied. Equilibrium dialysis binding measurements show that the apoprotein binds approximately 1.5 gm SDS per gram protein at high ionic strength (gamma/2 = 0.17). At low ionic strength (gamma/2 = 0.01) the protein binds only 0.90 gm per gram protein. The Stokes radius of the proteolipid protein is 40 A. Based on the circular dichroism spectrum, the apoprotein contains less than 20% alpha -helix structure in either aqueous or 0.1% sodium dodecyl sulfate solution. Analytical SDS-PAGE (polyacrylamide gel electrophoresis) revealed two polypeptides. The major proteolipid protein migrated with an apparent molecular weight of 26,000 daltons. The minor proteolipid protein exhibited a molecular weight of 22,200 daltons. The apoprotein showed a marked tendency to aggregate on 8 M urea-SDS-polyacrylamide gels or when heated at 100 degree in excess detergent. These results suggest that the proteolipid proteins have hydrophobic regions that are not embedded within the detergent micelle but are exposed to the solvent. These regions may serve as sites for intermolecular aggregation.
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Ting-Beall HP, Lees MB, Robertson JD. Interactions of Folch-Lees proteolipid apoprotein with planar lipid bilayers. J Membr Biol 1979; 51:33-46. [PMID: 522128 DOI: 10.1007/bf01869342] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Water-soluble Folch-Lees proteolipid apoprotein from bovine CNS white matter induces a voltage-dependent conductance in black lipid membranes. Na+ is required for the induced conductance change but the established conductance has very low ionic selectivity. The induced conductance fluctuates with a minimum amplitude of 10(-11)--10(-10) mho. The magnitude of the conductivity change is dependent on protein concentration and on the composition of lipid bilayers. At a fixed voltage the induced conductance of a phosphatidylcholine-cholesterol membrane is proportional to the sixth power of the protein concentration and the first power of Na+ concentration. The interactions between the apoprotein and the lipids are both electrostatic and hydrophobic, but the interaction leading to the conductance increase appears to be mainly hydrophobic. Both the increase in conductance and the current fluctuations remain after extensive washing of the chambers to remove the protein. Furthermore, pronase or glutaraldehyde added to either the cis or trans side of the membrane does not affect the apoprotein-established conductance. However, if the bilayer is formed in the presence of both the apoprotein and pronase or if the apoprotein is treated with pronase prior to its addition to the chamber, no conductance change is observed. The association of the apoprotein with the membrane thus appears to render the protein inaccessible to proteolytic digestion, suggesting that the apoprotein is at least partially imbedded in the membrane interior.
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Lees MB, Sakura JD, Sapirstein VS, Curatolo W. Structure and function of proteolipids in myelin and non-myelin membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 559:209-30. [PMID: 157777 DOI: 10.1016/0304-4157(79)90002-9] [Citation(s) in RCA: 84] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Lavialle F, de Foresta B, Vacher M, Nicot C, Alfsen A. The molecular size and shape of the Folch-Pi apoprotein in aqueous and organic solvents. EUROPEAN JOURNAL OF BIOCHEMISTRY 1979; 95:561-7. [PMID: 446482 DOI: 10.1111/j.1432-1033.1979.tb12997.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In 1% acetic acid, sedimentation velocity measurements and equilibrium ultracentrifuge experiments demonstrate that the Folch-Pi apoprotein is not monodisperse. The weight-average molecular weight calculated from ultracentrifuge experiments and combining sedimentation coefficient and viscosity measurements, ranged from 64000 to 80000. The intrinsic viscosity value suggests an asymetric shape for the apoprotein if a low value of hydration is considered. In dioxan/1% acetic acid (2:3, v/v) a smaller sedimentation coefficient was found, the intrinsic viscosity value remaining identical to that in 4% acetic acid. In pure 2-chloroethanol, light-scattering experiments led to a molecular weight of 165000 indicating that even in this solvent the protein is not monomeric. Intrinsic viscosity and light scattering measurements on the one hand, primary sequence on the other hand (six proline residues per monomer of Mr 23500) suggest that the molecule in 2-chloroethanol may consist of rod-like segments with flexible junctions.
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Jollès J, Schoentgen F, Jollès P, Vacher M, Nicot C, Alfsen A. Structural studies of the apoprotein of the Folch-Pi bovine brain myelin proteolipid : characterization of the CNBr-fragments and of a long C-terminal sequence. Biochem Biophys Res Commun 1979; 87:619-26. [PMID: 444242 DOI: 10.1016/0006-291x(79)91839-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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