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At least 19 recordsLinked to original sources
PubMed1990

Developmental study of proteolipids in bovine brain: a novel proteolipid and DM-20 appear before proteolipid protein (PLP) during myelination.

In a developmental study, we have shown that DM-20 is present before proteolipid protein (PLP) in the fetal bovine cerebral hemispheres. When the white matter appears (27-30 weeks of gestation), the amount of DM-20 drastically increases. DM-20 remains the major proteolipid until birth. PLP is detected only 2-4 weeks after the appearance of white matter, that is, more than 4 weeks after the appearance of DM-20. The early appearance of DM-20 at the beginning of myelination raises the question of its particular function. In the adult bovine cerebral hemispheres, PLP is the major proteolipid but DM-20 remains quantitatively important because the PLP/DM-20 ratio ranges from 1.5 to 1.7. In the same developmental study we have, in the fetal cerebral hemispheres, isolated and characterized a novel proteolipid (apparent Mr 20,000), which appears even before DM-20 and is not detected in the adult brain. It is structurally related to PLP and DM-20 because the first 31 N-terminal amino acid residues are the same. However, in immunoblot, it did not react either with the antitridecapeptide 117-129 antiserum of PLP or with the anti-C-terminal hexapeptide antiserum of PLP.

Animals↗
PubMed1987

[The DM-20 proteolipid is a major protein of the brain. It is synthetized in the fetus earlier than the major myelin proteolipid (PLP)].

By studying highly purified CNS proteolipids, we have shown that DM-20 proteolipid, which was considered, until now, to be a minor brain proteolipid is, in fact, almost as abundant as the Major Myelin Proteolipid known also as Proteolipid Protein (PLP). DM-20 proteolipid is even the major brain proteolipid in young foetuses. It is only during myelinisation that the "Proteolipid Protein" increases rapidly and becomes equivalent in weight to DM-20 proteolipid. This study raises the question of the particular function of DM-20 proteolipid.

Animals↗
PubMed1982

Interactions between bacterial pyrogen and proteolipid extracted from the cerebrum. (III). Variation in affinity of proteolipid proteins derived from rabbit, rat and chicken cerebrums to bacterial pyrogen.

We undertook comparative studies on the binding of cerebral proteolipids to LPS using rabbits, rats and chickens in order to clarify the differences in inactivating effects of proteolipids from these three sources on the pyrogenicity of LPS. The Sephadex LH-20 column elution profiles of lipid phosphorus and cerebrosides were not significantly different for the three sources of proteolipid, but a larger amount of proteolipid-protein possessing LPS pyrogenicity inactivating potency was eluted with chloroform (C)/methanol(M) (4:1) in rats and chickens than in rabbits. A complex of proteolipid-protein with LPS was obtained in C effluent from incubation mixtures of rat and chicken proteolipids with LPS, corresponding to our previous observation with rabbit proteolipid. The increasing order of binding capacity of the proteolipids derived from the three species was as follows: chicken, rat and rabbit, which was in parallel with pyrogenic inactivating potency. From these data, we suggest that the difference in pyrogenic inactivating potency among the proteolipids of some species depends on the difference in binding capacity of the proteolipids to LPS or probably lipid A.

Animals↗
PubMed1987

Cyst(e)ine residues of bovine white-matter proteolipid proteins. Role of disulphides in proteolipid conformation.

Cyst(e)ine residues of bovine white-matter proteolipid proteins were characterized in a highly purified preparation. From a total of 10.6 cyst(e)ine residues/molecule of protein, as determined by performic acid oxidation, 2.5-3 thiol groups were freely accessible to iodoacetamide, iodoacetic acid and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), when the proteins were solubilized in chloroform/methanol (C/M) (2:1, v/v). The presence of lipids had no effect on thiol-group exposure. One thiol group available to DTNB in C/M could not be detected when proteolipids were solubilized in the more polar solvent n-butanol. In a C/M solution of purified proteolipid proteins, SDS did not increase the number of reactive thiol groups, but the cleavage of one disulphide bridge made it possible to alkylate six more groups. C.d. and fluorescence studies showed that rupture of this disulphide bond changed the protein conformation, which was reflected in partial loss of helical structure and in a greater exposure to the solvent of at least one tryptophan residue. Cyst(e)ine residues were also characterized in the different components [PLP (principal proteolipid protein), DM20 and LMW (low-Mr proteins)] of the proteolipid preparation. Although the numbers of cyst(e)ine residues in PLP and DM20 were similar, in LMW fewer residues were alkylated under four different experimental conditions. The differences, however, are not simply related to differences in Mr.

Animals↗
PubMed1983

Isolation of cardiac membrane proteolipids by high pressure liquid chromatography. A comparison of reticular and sarcolemmal proteolipids, phospholamban and calciductin.

Membrane-bound phosphorylatable proteolipids were reported to play a role in the regulation of transmembrane Ca2+ fluxes by catecholamines. A generally applicable purification procedure is described by which such proteolipids as the cardiac sarcoplasmic reticulum phospholamban is purified by solvent extraction followed by high pressure liquid chromatography on microparticulate silica. Phospholamban is thereby purified with a yield of 3.37 mg from 100 mg of sarcoplasmic reticulum proteins, significantly higher than that obtained by any of the previously reported procedures. It appeared homogeneous upon dodecyl sulfate-polyacrylamide gel electrophoresis where it is stained by Coomassie blue and detected by autoradiography. The same procedure is applicable to cardiac sarcolemmal calciductin. Both proteolipids exhibit the same Mr 11 000 and pI 3.7 upon two-dimensional gel electrophoresis. Their amino acid compositions are very similar if not identical. This raises the intriguing possibility that phospholamban and calciductin are identical though they obviously belong to different membranes.

Amino Acids↗
PubMed2004

Analyses of proteolipid protein mutants show levels of proteolipid protein regulate oligodendrocyte number and cell death in vitro and in vivo.

Previous tissue culture studies indicate that the level of native proteolipid protein (PLP) or mutated PLP regulates the number of oligodendrocytes (Olgs). The regulation of Olg number is most likely due to toxicity of over-expression of native PLP or mis-sense mutations of PLP. We tested, in vivo and in vitro, the hypothesis that the absence of native PLP or reduced amounts of mutated PLP leads to an increase in numbers of Olgs and a corresponding decrease in the number of apoptotic Olgs. In cultures derived from PLP deficient mice, the number of Olgs is twofold greater than in wild-type mice. In primary glial cultures or in enriched OLG cultures, in which the synthesis of native PLP is blocked using antisense technology, the number of apoptotic cells is several-fold reduced. Injection of PLP antisense oligodeoxynucleotides into jimpy (jp) mice reduces the number of dying glia in spinal cord 3x compared to controls, and increased the number of myelinated fibers. These studies demonstrate that inhibition of native or mutant PLP synthesis directly reduces apoptosis. The regulation of apoptosis by PLP gene expression occurs independently of myelination, indicating that the PLP gene has multiple primary functions.

Animals↗
PubMed1998

T cell recognition of myelin proteolipid protein and myelin proteolipid protein peptides in the peripheral blood of multiple sclerosis and control subjects.

Myelin proteolipid protein (PLP) is a prime candidate autoantigen for multiple sclerosis. In order to define potential immunodominant epitopes, T cell lines (TCL) from the peripheral blood of HLA-DR 15(2) MS patients were established which responded to the intact molecule of PLP. These TCL were then tested in individual proliferation assays with a variety of PLP peptides spanning most of the PLP molecule. Multiple peptides were recognized by TCL from the MS population, with more than one peptide often recognized by lines from the same individual. Three immunodominant peptides were identified which were recognized by the majority of MS patients. Estimated frequency analyses were then performed on the peripheral blood of HLA-DR15(2)-positive MS and control subjects using TCL initiated by the three immunodominant peptides, 40-60, 95-117, and 185-206. TCL from HLA-DR15 MS subjects recognized peptide 95-117 significantly more often than TCL from control subjects.

Adult↗
PubMed2002

Overexpression of the myelin proteolipid protein leads to accumulation of cholesterol and proteolipid protein in endosomes/lysosomes: implications for Pelizaeus-Merzbacher disease.

Duplications and overexpression of the proteolipid protein (PLP) gene are known to cause the dysmyelinating disorder Pelizaeus-Merzbacher disease (PMD). To understand the cellular response to overexpressed PLP in PMD, we have overexpressed PLP in BHK cells and primary cultures of oligodendrocytes with the Semliki Forest virus expression system. Overexpressed PLP was routed to late endosomes/lysosomes and caused a sequestration of cholesterol in these compartments. Similar results were seen in transgenic mice overexpressing PLP. With time, the endosomal/lysosomal accumulation of cholesterol and PLP led to an increase in the amount of detergent-insoluble cellular cholesterol and PLP. In addition, two fluorescent sphingolipids, BODIPY-lactosylceramide and -galactosylceramide, which under normal conditions are sorted to the Golgi apparatus, were missorted to perinuclear structures. This was also the case for the lipid raft marker glucosylphosphatidylinositol-yellow fluorescence protein, which under normal steady-state conditions is localized on the plasma membrane and to the Golgi complex. Taken together, we show that overexpression of PLP leads to the formation of endosomal/lysosomal accumulations of cholesterol and PLP, accompanied by the mistrafficking of raft components. We propose that these accumulations perturb the process of myelination and impair the viability of oligodendrocytes.

Animals↗
PubMed1998

Myelin proteolipid protein intron 1 sequences do not appear to enhance myelin proteolipid protein gene transcription.

Sequences from the first intron of the mouse myelin proteolipid protein (PLP) gene were examined for their ability to modulate PLP gene expression. Glial (N20.1) or nonglial (NIH 3T3) cells were transiently transfected with constructs that contained 1.4 kb of PLP promoter sequence driving luciferase reporter gene expression, as well as various portions of PLP intron 1 DNA. Although these same PLP intron 1 fragments enhanced reporter gene expression from a heterologous basal promoter in a previous study, the results reported here demonstrate that they do not augment PLP promoter activity. Thus, the regulation of PLP cell-type-specific expression, conferred by the first intron, appears to be mediated by an enhancer-independent mechanism.

3T3 Cells↗
PubMed2002

Overexpression of the 3'-untranslated region of myelin proteolipid protein mRNA leads to reduced expression of endogenous proteolipid mRNA.

The current studies focus on what mechanisms regulate the concentration of PLP mRNA in cells. The PLP mRNA is very stable and these studies suggest that its stability is regulated by a trans-acting factor specific to oligodendrocytes. In order to test whether the 3'untranslated region (3'UTR) of the PLP mRNA might regulate PLP RNA stability, C6 cells were transfected with cDNAs that expressed either luciferase or luciferase fused to the 3'UTR of PLP. Although transgene expression was low, in cells transfected with the PLP 3'UTR, there was a significant decrease in the endogenous PLP mRNA. These cells showed a distinct change in morphology and in adhesion properties. Thus, there may be a role for plp gene products in cell adhesion, which was downregulated in these cells, or an unknown function may be encoded by the PLP 3'UTR. Transgenic mice that overexpress enhanced green fluorescent protein fused to the PLP 3'UTR under control of PLP regulatory sequences were tested for the expression of the endogenous PLP mRNA. Three of four lines of transgenic mice had decreased endogenous PLP mRNA, relative to their non-transgenic littermates; the EGFP-PLP 3'UTR mouse line that expressed the highest level of transgene mRNA had a 54% reduction in PLP mRNA. We hypothesize that the PLP mRNA is regulated by elements in the 3'UTR and stabilizing proteins specific to oligodendrocytes, and that in cells that overexpress the PLP 3'UTR, these stabilizing proteins may be insufficient to maintain the normal level of the endogenous PLP mRNA.

3' Untranslated Regions↗
PubMed2001

Classic and soma-restricted proteolipids are targeted to different subcellular compartments in oligodendrocytes.

The myelin proteolipid (PLP) gene is very active in oligodendrocytes (OLs) and generates at least four proteins: the classic PLP and DM20 proteolipids, which are associated with compact myelin and the srPLP and srDM20, which are associated with the cell soma. These proteins are extremely hydrophobic and appear to follow the biosynthetic route used by secretory proteins. In this study, we have analyzed the subcellular distribution of the newly described sr-proteolipids and compared it to that of the classic proteolipids. Immunocytochemical analysis indicates that the sr-proteolipids and classic proteolipids are found in association with the endoplasmic reticulum (ER) and Golgi apparatus of mature OLs in vitro. Whereas the classic proteolipids become associated with the myelin-like sheets elaborated by OLs, the sr-proteolipids are not targeted to the myelin leaflets. The sr-proteolipids were associated with endosomes and with recycling vesicles as determined by double immunocytochemistry with markers such as syntaxin 6 and clathrin. In vivo, immunohistochemical analysis showed a distribution of the sr-proteolipids that was similar to that obtained in vitro, with a total absence of incorporation of sr-proteolipids into compact myelin. This differential subcellular localization is further evidence for a biological role for these products of the PLP/DM20 gene, which is different from that of the classic proteolipids.

Animals↗
PubMed1988

Ion-translocating properties of calcifiable proteolipids.

De novo formation of calcium hydroxyapatite in biological systems occurs on membrane surfaces through specific interactions of Ca, Pi, phospholipids, calcifiable proteolipids, and ion flux to and from the nucleating site. This paper reports an in vitro model demonstrating an ion transport function for calcifiable proteolipid. Bacterionema matruchotii proteolipid was incubated with a radiolabeled H+-channel inhibitor, 14C-dicyclohexyl-carbodiimide, and binding characterized by displacement studies with DCCD or ethyldimethylaminopropylcarbodiimide. A carboxyl binding site was suggested by displacement of DCCD by the nucleophile, glycine ethyl ester. The displacement studies indicated that proteolipid bound DCCD via carboxyl group interaction in a hydrophobic region of the protein. SDS-polyacrylamide gel electrophoresis showed that all label was associated with a single band of 8500 Mr. No non-specific binding of 14C-DCCD to phospholipids occurred, since all bound label was associated with protein following Sephadex LH-20 chromatography of crude proteolipid. Phospholipid liposomes were prepared containing bacteriorhodopsin and proteolipid or proteolipid-14C-DCCD, via cholate dialysis. Transmembrane pH changes established by the bacteriorhodopsin H+ pump were measured in the presence and absence of added proteolipid. Proteolipid had an effect similar to those of uncouplers such as tetraphenylboron. Both the rate and extent of proton translocation increased following addition of proteolipid to BR-liposomes. 14C-DCCD abolished the proteolipid-augmented ion transport. When tetraphenylboron was used to abolish the transmembrane electrical potential, calcifiable proteolipid did not augment proton transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Actinomycetaceae↗
PubMedDate not supplied

[Method of extracting brain proteolipids].

From the whole brain of animals representing 5 classes of vertebrates--mammals (Macaca rhesus and albino rat), birds (the pigeon Columba livia), reptiles (the tortoise Testudo horsfieldi), amphibians (the frog Rana temporaria) and fishes (the trout Salmo irideus), as well as from myelin preparations of mammals (dog, rabbit and rat) proteolipids have been isolated by emulsion--centrifugation method. It was shown that extraction procedure results in the loss and destruction of several proteolipid complexes. In all the animals investigated, the main loss (from 25 to 75% of all complexes) was observed during emulsion--centrifugation stage, especially during 10-min centrifugation at 200 g. During extraction of proteolipids from the whole brain, under the conditions employed, the lost proteolipids are presumably those which belong to the myelin fraction. To prevent excessive proteolipid loss, the final low speed centrifugation step should be avoided. It was shown that in order to obtain proteolipids in a soluble form in a mixture of chloroform and methanol, total proteolipids from the brain of mammals should contain not less than 27% of phospholipids. Studies were also made on the composition and relative content of phospholipids in proteolipids extracted from the whole mammalian brain and myelin preparations. With respect to phospholipid composition, proteolipids from the whole brain significantly differ from those obtained from myelin fraction. Myelin fraction, being itself rich in proteolipids, contain large amounts of phosphatidyl serine (up to 69); however, proteolipids of this fraction contain lower amounts (4%) of diphosphatidyl glycerol as compared to proteolipids from the whole brain (22%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Brain proteolipids in representatives of different vertebrate classes].

The Folch-Lees proteolipid complexes of different purity (crude proteolipids and relative pure proteolipids) were isolated from vertebrate brain: mammalia (Macaca irus, Macaca rhesus and white rat), birds (Columbia livia), reptilia (Testudo horsfieldi), amphibia (Rana temporaria) and fishes (Salmo irideus). The proteolipid complexes were isolated by emulsion-centrifugation method. The content of proteolipid protein (mg/g w. w.) correlates with the level of phylogenetic development of the animals studied. It is the highest in monkey brain (10.5 and 8.6 mg/g) and the lowest in fish brain (2.2 mg/g). The yield of proteolipids from the brains of animals studied shows the same pattern. Crude proteolipids of mammalia, birds and reptiles contain 40-50% of protein and 60-50% of lipids. The content of phospholipids is about 40%. Proteolipids of amphibia and fish brain contain less protein--about 30%. In the conditions of mild purification, the protein content in mammalia, birds and reptilia makes up about 70% and lipid content--about 30-35%. The crude and purified proteolipids in all the animals studied (as compared with the original lipid extracts from which they were isolated) are enriched in acid phospholipids: phosphatidyl serine, phosphatidyl inositol and diphosphatidyl glycerol. Acid phospholipids in total lipid extract make up 10-20% of total phospholipids, in crude proteolipids 16-32 and in purified proteolipids--56-75%. There are no marked differences between fatty acid composition of phospholipids in proteolipids and in the same phospholipids isolated from total lipid extract.

Animals↗
PubMed1987

Structure and expression of the mouse myelin proteolipid protein gene.

The gene for the mouse myelin proteolipid protein has been isolated and the seven exons have been sequenced. Since the sequence of a rat proteolipid protein cDNA and partial sequence of the human proteolipid protein gene have been determined, it was possible to demonstrate a very high degree of conservation for the proteolipid protein gene exons among species. While there are some nucleotide changes, the protein coding region of the mouse gene encodes protein that is totally conserved relative to both rat and human proteolipid proteins. The regulatory and noncoding regions of the proteolipid protein gene are also highly conserved. The upstream regulatory and 5'-noncoding region of the gene is 92% homologous to the comparable region of the human proteolipid protein gene, and the 3'-noncoding region of the mouse gene is approximately 90% homologous to a rat proteolipid protein cDNA through 2,200 nucleotides of 3'-noncoding DNA. S1 nuclease protection experiments indicated that the major 5'-end for proteolipid protein mRNAs from mouse, rat, human, or baboon is approximately 147-160 nucleotides upstream from the initial methionine codon of the protein coding region. Other S1 nuclease protection experiments indicated the possible existence of an alternative splice site within exon 3, which may produce mRNA for DM20. This mRNA is approximately 100 nucleotides shorter than that for the proteolipid protein, and it is missing the latter half of exon 3, that is, amino acids 116-150 of the proteolipid protein sequence.

Amino Acid Sequence↗