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Appadu A, Jelokhani-Niaraki M, DeBruin L. Conformational Changes and Association of Membrane-Interacting Peptides in Myelin Membrane Models: A Case of the C-Terminal Peptide of Proteolipid Protein and the Antimicrobial Peptide Melittin. J Phys Chem B 2015; 119:14821-30. [DOI: 10.1021/acs.jpcb.5b07375] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ashtina Appadu
- Department
of Chemistry and
Biochemistry, Wilfrid Laurier University, 75 University Ave. W., Waterloo, Ontario, Canada N2L 3C5
| | - Masoud Jelokhani-Niaraki
- Department
of Chemistry and
Biochemistry, Wilfrid Laurier University, 75 University Ave. W., Waterloo, Ontario, Canada N2L 3C5
| | - Lillian DeBruin
- Department
of Chemistry and
Biochemistry, Wilfrid Laurier University, 75 University Ave. W., Waterloo, Ontario, Canada N2L 3C5
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Yin X, Kiryu-Seo S, Kidd GJ, Feltri ML, Wrabetz L, Trapp BD. Proteolipid protein cannot replace P0 protein as the major structural protein of peripheral nervous system myelin. Glia 2014; 63:66-77. [PMID: 25066805 DOI: 10.1002/glia.22733] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Accepted: 07/14/2014] [Indexed: 11/10/2022]
Abstract
The central nervous system (CNS) of terrestrial vertebrates underwent a prominent molecular change when proteolipid protein (PLP) replaced P0 protein as the most abundant protein of CNS myelin. However, PLP did not replace P0 in peripheral nervous system (PNS) myelin. To investigate the possible consequences of a PLP to P0 shift in PNS myelin, we engineered mice to express PLP instead of P0 in PNS myelin (PLP-PNS mice). PLP-PNS mice had severe neurological disabilities and died between 3 and 6 months of age. Schwann cells in sciatic nerves from PLP-PNS mice sorted axons into one-to-one relationships but failed to form myelin internodes. Mice with equal amounts of P0 and PLP had normal PNS myelination and lifespans similar to wild-type (WT) mice. When PLP was overexpressed with one copy of the P0 gene, sciatic nerves were hypomyelinated; mice displayed motor deficits, but had normal lifespans. These data support the hypothesis that while PLP can co-exist with P0 in PNS myelin, PLP cannot replace P0 as the major structural protein of PNS myelin.
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Affiliation(s)
- Xinghua Yin
- Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio
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Lund BT, Chakryan Y, Ashikian N, Mnatsakanyan L, Bevan CJ, Aguilera R, Gallaher T, Jakowec MW. Association of MBP peptides with Hsp70 in normal appearing human white matter. J Neurol Sci 2006; 249:122-34. [PMID: 16842822 DOI: 10.1016/j.jns.2006.05.066] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Revised: 05/04/2006] [Accepted: 05/26/2006] [Indexed: 10/24/2022]
Abstract
Multiple Sclerosis is an autoimmune disease directed against myelin proteins. The etiology of MS is poorly defined though, with no definitive causative agent yet identified. It has been hypothesized that MS may be a multifactorial disease resulting in the same end product: the destruction of myelin by the immune system. In this report we describe a potential role for heat shock proteins in the pathogenesis of MS. We isolated Hsp70 from the normal appearing white matter of both MS and normal human brain and found this was actively associated with, among other things, immunodominant MBP peptides. Hsp70-MBP peptide complexes prepared in vitro were shown to be highly immunogenic, with adjuvant-like effects stimulating MBP peptide-specific T cell lines to respond to normally sub-optimal concentrations of peptide. This demonstration of a specific interaction between Hsp70 and different MBP peptides, coupled with the adjuvanticity of this association is suggestive of a possible role for Hsp70 in the immunopathology associated with MS.
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Affiliation(s)
- Brett T Lund
- Department of Neurology, Keck School of Medicine, University of Southern California, McKibben Annex, Room 246, 1333 San Pablo Street, Los Angeles, California 90033, United States.
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Bizzozero OA, Howard TA. Myelin proteolipid protein-induced aggregation of lipid vesicles: efficacy of the various molecular species. Neurochem Res 2002; 27:1269-77. [PMID: 12512933 DOI: 10.1023/a:1021659313213] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The different molecular species that form the myelin proteolipid protein family were isolated by size-exclusion and ion-exchange chromatography in organic solvents and their adhesive properties were tested using a vesicle aggregation assay. Addition of the major proteolipid (PLP) to phosphatidylcholine-cholesterol vesicles caused their clustering as determined by increase in O.D.(450 nm) and by transmission electron microscopy. A small fraction of the aggregated vesicles underwent fusion as determined by resonance energy transfer experiments. Vesicle aggregation by PLP, but not the dissociation of the aggregates, was influenced by pH suggesting that electrostatic interactions are important only during cluster formation. Cleavage of disulfide bonds and methylation of carboxyl groups in PLP greatly reduced the aggregating activity, indicating that the process is dependent on the protein's conformation. Unexpectedly, the proteolipid DM-20 was also effective at inducing the clustering of neutral lipid vesicles. In contrast, three protein fractions comprising the naturally-occurring PLP fragments 1-107/112, 113/125-276 and 129/131-276, bearing different net charges, displayed a much lower activity. In addition, trypsin digestion of PLP resulted in a progressive decrease in the protein's ability to induce vesicle aggregation which coincided with the disappearance of the full-length molecule. Together, these results suggest that even large PLP fragments cannot fulfill the adhesive function of the intact protein.
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Affiliation(s)
- Oscar A Bizzozero
- Department of Cell Biology and Physiology, University of New Mexico, Health Sciences Center, Albuquerque, New Mexico 87131, USA.
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Bizzozero OA, Bixler HA, Davis JD, Espinosa A, Messier AM. Chemical deacylation reduces the adhesive properties of proteolipid protein and leads to decompaction of the myelin sheath. J Neurochem 2001; 76:1129-41. [PMID: 11181833 DOI: 10.1046/j.1471-4159.2001.00116.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Myelin proteolipid protein (PLP) contains thioester-bound, long-chain fatty acids which are known to influence the structure of the molecule. To gain further insights into the role of this post-translational modification, we studied the effect that chemical deacylation of PLP had on the morphology of myelin and on the protein's ability to mediate the clustering of lipid vesicles. Incubation of rat optic nerves in isoosmotic solutions containing 100 mM hydroxylamine (HA) pH 7.4 led to deacylation of PLP and decompaction of myelin lamellae at the level of the intraperiod line. Incubation of nerves with milder nucleophilic agents (Tris and methylamine) or diluted HA, conditions that do not remove protein-bound fatty acids, caused no alterations in myelin structure. Other possible effects of HA which could have affected myelin compaction indirectly were ruled out. Incubation of optic nerves with 50 mM dithioerythritol (DTE) also led to the splitting of the myelin intraperiod line and this change again coincided with the removal of fatty acids. In addition, the apparently compacted CNS myelin in the PLP-less myelin-deficient rat, like that in tissue containing deacylated PLP, was readily decompacted upon incubation in isoosmotic buffers, suggesting that the function of PLP as a stabilizer of the interlamellar attachment is, at least in part, mediated by fatty acylation. Furthermore, in contrast to the native protein, PLP deacylated with either HA or DTE failed to induce the clustering of phosphatidylcholine/cholesterol vesicles in vitro. This phenomenon is not due to side-effects of the deacylation procedure since, upon partial repalmitoylation, the protein recovered most of its original vesicle-clustering activity. Collectively, these findings suggest that palmitoylation, by influencing the adhesive properties of PLP, is important for stabilizing the multilamellar structure of myelin.
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Affiliation(s)
- O A Bizzozero
- Department of Cell Biology and Physiology, University of New Mexico-Health Sciences Center, Albuquerque, New Mexico, USA.
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Chávez A, Pujol M, Haro I, Alsina MA, Cajal Y. Membrane fusion by an RGD-containing sequence from the core protein VP3 of hepatitis A virus and the RGA-analogue: implications for viral infection. Biopolymers 2001; 58:63-77. [PMID: 11072230 DOI: 10.1002/1097-0282(200101)58:1<63::aid-bip70>3.0.co;2-l] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The interaction of an RGD-containing epitope from the hepatitis A virus VP3 capsid protein and its RGA-analogue with lipid membranes was studied by biophysical methods. Two types of model membrane were used: vesicles and monolayers spread at the air/water interface, with a composition that closely resembles the lipid moiety of hepatocyte membranes: PC/SM/PE/PC (40:33:12:15; PC: 1-palmitoyl-2-oleoylglycero-sn-3-phosphocholine; SM: sphingomyelin from chicken egg yolk; PE, 1,2-dipalmitoyl-phosphatidylethanolamine; PS: L-alpha-phosphatidyl-L-serine from bovine brain). In addition, zwitterionic PC/SM/PE (47:39:14) and cationic PC/SM/PE/DOTAP (40:33:12:15; DOTAP: 1,2-dioleoyl-3-trimethylammonium-propane) membranes were also prepared in order to dissect the electrostatic and hydrophobic components in the interaction. Changes in tryptophan fluorescence, acrylamide quenching, and resonance energy transfer experiments in the presence of vesicles, as well as the kinetics of insertion in monolayers, indicate that both peptides bind to the three types of membrane at neutral and acidic pH; however, binding is irreversible only at low pH. Membrane-destabilizing and fusogenic activities are triggered by acidification at pH 4-6, characteristic of the endosome. Fluorescence experiments show that VP3-RGD and VP3-RGA induce mixing of lipids and leakage or mixing of aqueous contents in anionic and cationic vesicles at pH 4-6, indicating leaky fusion. Interaction with zwitterionic vesicles (PC/SM/PE) results in leakage without lipid mixing, indicating pore formation. Replacement of aspartic acid in the RGD motif by alanine maintains the membrane-destabilizing properties of the peptide at low pH, but not its antigenicity. Since the RGD tripeptide is related to receptor-mediated cell adhesion and antigenicity, results suggest that receptor binding is not a molecular requirement for fusion. The possible involvement of peptide-induced membrane destabilization in the mechanism of hepatitis A virus infection of hepatocytes by the endosomal route is discussed.
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Affiliation(s)
- A Chávez
- Department of Physical Chemistry, School of Pharmacy, University of Barcelona, Avn. Joan XXIII s/n, 08028 Barcelona, Spain
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Palaniyar N, Semotok JL, Wood DD, Moscarello MA, Harauz G. Human proteolipid protein (PLP) mediates winding and adhesion of phospholipid membranes but prevents their fusion. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1415:85-100. [PMID: 9858696 DOI: 10.1016/s0005-2736(98)00180-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
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.
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Affiliation(s)
- N Palaniyar
- Department of Molecular Biology and Genetics, The University of Guelph, 50 Stone Road East, Guelph, Ont. N1G 2W1, Canada
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van der Haar ME, Visser HW, de Vries H, Hoekstra D. Transport of proteolipid protein to the plasma membrane does not depend on glycosphingolipid cotransport in oligodendrocyte cultures. J Neurosci Res 1998; 51:371-81. [PMID: 9486772 DOI: 10.1002/(sici)1097-4547(19980201)51:3<371::aid-jnr10>3.0.co;2-a] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The possibility that transport of proteolipid protein (PLP) from its site of synthesis to the plasma membrane is dependent on cotransport with (sulfo)galacto-cerebrosides was investigated in primary cultured oligodendrocytes and Chinese hamster ovary (CHO) cells expressing PLP. Sulfation was inhibited by growing oligodendrocytes in the presence of a competitive inhibitor of this process, sodium chlorate. Under these circumstances, sulfatide synthesis was inhibited by 85%. Nevertheless, PLP was still delivered to the plasma membrane in quantitative amounts. Furthermore, when PLP was expressed in CHO cells, which normally synthesize very low amounts of galactosyl ceramide (GalCer) and no sulfatide, PLP was transported to the plasma membrane. Moreover, in CHO cells coexpressing PLP and ceramide galactosyl transferase, PLP cell surface labeling was unaltered. Noting that it has been demonstrated that proteins destined for the apical surface of epithelial cells colocalize with glycolipid-enriched microdomains, we isolated detergent-insoluble membrane complexes from cultured oligodendrocytes. We found, however, that most of the PLP is present in the detergent-soluble fraction and, furthermore, that PLP could not be chased into or out of the insoluble fraction. Taken together, these data make it very likely that in oligodendrocytes PLP transport takes place irrespective of the presence of glycosphingolipids GalCer and sulfatide.
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Affiliation(s)
- M E van der Haar
- Department of Physiological Chemistry, Faculty of Medical Sciences, University of Groningen, The Netherlands
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