Partial characterization of basic proteins of chicken, turtle and frog central nervous system myelin

Characterization of turkey myelin basic protein isolated by a simple procedure

Highly purified basic proteins have been isolated from bovine and turkey brains by a novel method employing acid-acetone extraction. The final product gave a single band on polyacrylamide gel electrophoresis at pH 4.3 and in the presence of sodium dodecyl sulfate. Both proteins have arginine at the COOH-terminus while the NH2-terminal residue cannot be detected and is probably blocked. A higher ratio of histidine to lysine and a greater proportion of serine and valine was found for the turkey compared with the bovine protein. Both proteins contain one tryptophan and two methionine residues. However, it was found from cyanogen bromide treatment that there is a marked difference in the location of one of the methionine residues, while the tryptophan-containing peptides liberated after trypsin digestion have different mobilities on peptide maps. When dissolved in water these proteins give a typical random coil curve from circular dichroism (CD), whereas in 80% methyl alcohol they assume a 25% alpha-helix.

Xenopus IRBP, a phylogenetically remote protein, is uveitogenic in Lewis rats

Mammalian interphotoreceptor retinoid-binding proteins (IRBPs) are highly uveitogenic in Lewis rats. Xenopus laevis IRBP resembles mammalian IRBP in its four-fold structure, and has approximately 70% amino acid sequence identity with the bovine protein. This study investigated the uveitogenicity of recombinant Xenopus IRBP and two of its derived peptides in Lewis rats. Rats immunized with Xenopus IRBP developed uveoretinitis as well as pineal inflammation. The Xenopus molecule was, however, less immunopathogenic than the bovine IRBP. Of the two Xenopus IRBP peptides tested, 1180-1191 was remarkably uveitogenic, whereas sequence 521-540 exhibited low activity. It is assumed, therefore, that as with bovine IRBP, peptide 1180-1191 is the major uveitogenic sequence in Xenopus IRBP. The role individual residues of these peptides play in the immunopathogenic process is discussed. Our data thus demonstrate that despite its being phylogenetically remote, Xenopus IRBP is uveitogenic in Lewis rats

Developmental accumulation and heterogeneity of myelin basic protein transcripts in the chick visual system

By selective cloning of gene products newly expressed in the developing chick optic tectum, we have isolated cDNA clones encoding myelin basic protein (MBP). Three different transcripts of the corresponding single copy gene of 2.7 kb, 2.0 kb, and 1.1 kb were observed on Northern blots. In the developing optic lobe, the most abundant RNA (2.7 kb) was detected first at the 14th day in ovo. Nuclease S1 protection experiments revealed further heterogeneity of MBP transcripts, which result from alternative splicing of segments corresponding to the fifth and sixth exon of the homologous murine MBP gene. From these data, at least three different forms of MBP are predicted to exist in the chicken central nervous system.

Characterization of a novel monoclonal anti-myelin basic protein antibody: use in immunoblotting and immunohistochemical studies

Monoclonal antibodies (MAbs) to the myelin basic protein (MBP) were produced in CAF1 (BALB/c x A/J) mice immunized with intact bovine MBP. A number of MAbs were obtained, one of which was characterized in detail with respect to its isotype, antigenic determinant on the MBP, the spectrum of antigens with which it reacted in mouse brain, and its immunohistochemical staining characteristics. This monoclonal, GB-1 (an IgG1), recognized an epitope within residues 30-51 of bovine MBP. It also reacted with a family of MBP-related proteins present in brain homogenates of mice from 7-35 days. Immunohistochemically, GB-1 stained myelinated fibers and oligodendrocytes in the rodent CNS. A second monoclonal (GB-2, and IgM) was partially characterized. It reacted with intact MBP when it was immobilized to plastic or nitrocellulose, but it was not found to be useful for immunoblots or immunohistochemistry.

Immunohistochemical localization of myelin basic protein in the developing optic system of trout

Immunofluorescent localization of basic protein (BP) in the CNS of trout was performed using a heterologous antiserum raised against human BP. Bright specific fluorescence was confined to the myelin sheath of axons in most regions of the brain, whereas neuronal pericarya and dendrites as well as glial cells were entirely negative. In the tectum immunofluorescence was characteristically distributed in two rows of horizontally aligned patches, most evidently reflecting the orderly array of myelinated fiber bundles in the stratum opticum and stratum album. During development of the retino-tectal pathway, the appearance of BP followed a distinct rostro-caudal gradient firstly reaching the anterior ventral border of the tectum by larval stage 34. Furthermore, on cross sections through the optic nerve a specifically organized pattern of myelin formation was revealed by immunohistochemistry, which strikingly coincided with the pattern of fiber outgrowth.

CSF antibodies to myelin basic protein and to myelin-associated glycoprotein in multiple sclerosis. Evidence of the intrathecal production of antibodies

Cerebrospinal fluid (CSF) from 40 multiple sclerosis (MS) patients was tested by solid-phase radioimmunoassay (RIA) for ability to bind 2 common structural components of myelin and oligodendroglia, i.e., to bind myelin basic protein (MBP) and myelin-associated glycoprotein (MAG). To prevent the effect of differences in CSF IgG concentration on binding activity, the CSF samples were tested at equal IgG concentration 1 mg/ml. The mean binding activity to MBP and MAG was significantly higher than in control neurotics, respectively P less than or equal to 0.05 and P less than or equal to 0.001. In 33% of MS cases, CSF antibody against both antigens was found. Indirect data were obtained that autoantibodies whose antigens are associated with myelin-oligodendrocyte unit are produced locally within the central nervous system (CNS). Anti-MAG and anti-MBP CSF antibody activity was significantly higher, P less than or equal to 0.01 for both antibody specificity, in MS cases characterized by high IgG Index, greater than or equal to 0.70 = means + SD in the neurotic group, versus MS cases characterized by normal IgG Index (less than or equal to 0.70). Correlation coefficient between antibody activity and IgG Index values was 0.785 for anti-MBP antibody, and 0.400 for anti-MAG antibody. The importance of intrathecally produced antibody to MBP and MAG lies in the fact that it indicates an active humoral autoimmune process against a myelin-oligodendrocyte unit in which more than one autoantigen is involved.

In vivo incorporation of [32P]orthophosphate into myelin basic protein of developing rabbit brain: its location in components 3 and 5 and in a new protein tentatively identified as basic protein component 7

Myelin was isolated from the brains of 16-day-old rabbits that had received intracerebral injections of [32P]orthophosphate 24 h earlier. The basic protein was extracted and examined by polyacrylamide gel electrophoresis both at low and at high pH. At low pH a single band corresponding to the basic protein contained all of the covalently bound protein radioactivity. At high pH, three bands of radioactivity corresponding to basic protein components 3, 5, and 7 were observed. Estimation of the specific radioactivities of the components in conjunction with their high pH electrophoretic mobilities indicated that components 3, 5, and 7 contained one, two, and three phosphate groups per molecule of protein, respectively.

Basic protein in brain myelin is phosphorylated by endogenous phospholipid-sensitive Ca2+-dependent protein kinase

Phosphorylation of myelin basic protein (MBP) in rat or rabbit brain myelin was markedly stimulated by Ca2+, and this reaction was not essentially augmented by exogenous phosphatidylserine or calmodulin or both. Solubilization of myelin with 0.4% Triton X-100 plus 4 mM EGTA, with or without further fractionation, showed that Ca2+-dependent phosphorylation of MBP required phosphatidylserine, but not calmodulin. DEAE-cellulose chromatography of solubilized myelin revealed a pronounced peak of protein kinase activity stimulated by a combination of Ca2+ and phosphatidylserine; a protein kinase stimulated by Ca2+ plus calmodulin was not detected. These findings clearly indicate an involvement of phospholipid-sensitive Ca2+-dependent protein kinase in phosphorylation of brain MBP, although a possible role for the calmodulin-sensitive species of Ca2+-dependent protein kinase in this reaction could not be excluded or established. Phosphorylation of MBP in solubilized rat myelin catalyzed by the phospholipid-sensitive enzyme was inhibited by adriamycin, palmitoylcarnitine, trifluoperazine, melittin, polymyxin B, and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7).

In vivo methylation of an arginine in chicken myelin basic protein

The amino acid sequence around the sole methylarginine residue in chicken myelin basic protein was determined and was found to be similar to that previously reported for mammalian myelin basic protein. The ratio NG, N'G-dimethylarginine: NG-monomethylarginine:arginine was approximately 1.3:0.9:1.0. No NG, NG-dimethylarginine was detected in the protein. The in vivo incorporation of methyl groups from [methyl-3H]methionine into methylarginines in myelin was found to occur readily in 2-day-old chickens. Radioactively labelled NG,N'G-dimethylarginine and NG-monomethylarginine in myelin were derived solely from myelin basic protein. Radioactivity was also incorporated into NG,NG-dimethylargnine, although this was not derived from myelin basic protein. As NG-monomethylarginine was easily separated from the dimethylarginines, and as it was derived from myelin basic protein, it may be a good marker for myelin basic protein turnover in vivo. A time course study of the incorporation showed that radioactivity was incorporated into NG-monomethylarginine up to 6 h after injection, and decayed slowly, with an apparent half-life of about 40 days.

Phosphorylation in vivo of four basic proteins of rat brain myelin

When rat brain myelin was examined by sodium dodecyl sulphate/polyacrylamideslab-gel electrophoresis followed by fluorography of the stained gel, it was found that a host of proteins of rat brain myelin were labelled 2, 4 and 24h after the intracerebral injection of H(3) (32)PO(4). Among those labelled were proteins migrating to the positions of myelin-associated glycoprotein, Wolfgram proteins, proteolipid protein, DM-20 and basic proteins. The four basic proteins with mol.wts. 21000, 18000 (large basic protein), 17000 and 14000 (small basic protein) were shown to be phosphorylated after electrophoresis in both acid-urea- and sodium dodecyl sulphate-containing gel systems followed by fluorography. The four basic proteins imparted bluish-green colour, after staining with Amido Black, which is characteristic of myelin basic proteins. The four basic proteins were purified to homogeneity. Fluorography of the purified basic proteins after re-electrophoresis revealed the presence of phosphorylated high-molecular-weight ;polymers' associated with each basic protein. The amino acid compositions of the phosphorylated large basic protein and small basic proteins are compatible with the amino acid sequences. Proteins with mol.wts. 21000 and 17000 gave the expected amino acid composition of myelin basic proteins. Radiolabelled phosphoserine and phosphothreonine were identified after partial acid hydrolysis of the four purified basic proteins. The [(32)P]phosphate-protein bond in the basic protein was stable at an acidic pH but was readily hydrolysed at alkaline pH, as would be expected of phosphoester bonds involving both serine and threonine residues. Double-immunodiffusion analysis demonstrated that the four phosphorylated proteins showed complete homology when diffused against antiserum to a mixture of small and large basic proteins. Since the four basic proteins of rat brain myelin were phosphorylated both in vivo and in vitro it is postulated that the same protein kinase is responsible for their phosphorylation in both conditions.

A comparative study of the immunohistochemical localization of basic protein to myelin and oligodendrocytes in rat and chicken brain

Antisera to highly purified basic protein (BP) from rat and chicken brain were prepared and their purity and specificity demonstrated by double immunodiffusion and cross-immunoadsorption. These antisera were used for immunohistochemical localization of BP in the brains of adult and developing rat and chick. Myelin basic protein was exclusively localized to myelin or the myelin forming elements of the CNS. It was present in high concentrations in white matter and absent in areas free of myelin. Neuronal parikarya and dendrites were negative as were axons cut in cross section and at Nodes of Ranvier. The latter was best observed in cross sections of human spinal cord demonstrating also the immunoreactivity of the antibodies with human BP. The internodal distance in a fine (1.5 micrometer) rat cortical fiber was determined to be approximately 45 micrometers. Myelin basic protein was shown to extend into cranial roots, in contrast to myelin proteolipid protein which abruptly lose fluorescence as the nerves emerged from the brain. During development, BP was first observed on the fourteenth day of incubation in chick and at birth in the rat. The protein appeared in oligodendrocytes and in association with fibers near these cells. Fluorescent processes were frequently observed connecting the oligodendrocytes with the fibers. As myelination progressed, the intensity of the immunohistochemical reaction decreased in the oligodendrocytes while the brightness in fibers increase. Eventually, the oligodendrocytes became undetectable. Fibers with immature myelin exhibited a beaded or varicosed appearance with the highest concentration of immunofluorescence in the outer portion of the varicosities. The varicosities were postulated to represent dilations in the newly forming sheath between intervals of compaction along the axon undergoin myelination. These dilations might represent areas of increased cytoplasmic volume which could serve as channels for transport and/or storage sites for myelin proteins prior to incorporation into the membrane. The varicosities became less prominent with the thickening of the myelin sheath and mature myelinated fibers became smooth. The process of synthesis of BP, transport of the protein to the varicosed fibers, and maturation of the myelin sheath was seen to progress in a more or less caudal to rostral direction as myelination of the CNS takes place. In the rat, this was accomplished over approximately a 30-day period starting near the time of birth. In the chick, most of the myelination was accomplished in the three or four days immediately before hatching. At this time, innumerable oligodendrocytes were observed producing BP simultaneously in the major white fiber tracts. It is postulated that in chick some degree of oligodendrocytic cell death occurs normally during myelination.

A biochemical comparison of Xenopus laevis and mammalian myelin from the central and peripheral nervous systems

Myelin purified from the central nervous system of Xenopus laevis contained the same major lipid and protein components as human myelin. However, some minor differences in the myelin proteins were noted. The Xenopus basic protein had a higher apparent mol wt. on sodium dodecyl sulfate gels than the corresponding mammalian protein. The absolute specific activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase in the Xenopus myelin was considerably higher than in mammals. There were differences in the high mol wt. proteins, and the glycoproteins in Xenopus myelin were more heterogeneous than those in mammals. Peripheral myelin from Xenopus sciatic nerve was compared with that from the rat. The lipids in the two types of myelin were similar. There was a major glycoprotein in the Xenopus myelin corresponding to the P0 protein and a basic protein of slightly larger mol wt. than the P1 protein of rat myelin.

Immunochemical comparisons among myelin basic proteins

1. The relationships among myelin encephalitogenic or basic proteins were immunochemically examined. 2. Rabbit antisera to myelin basic proteins isolated from chicken, rabbit, bovine, guinea-pig, and human brain specimens were prepared. By quantitative microcomplement fixation these rabbit antisera were used to measure cross-reactions among the myelin basic proteins of the turtle, chicken, rat, rabbit, cow, pig, sheep, dog, guinea-pig, monkey and human. 3. A spectrum of cross-reactivities was detected even though some cross-reactivity persisted across major phylogenetic barriers. Varying, but sometimes marked, differences existed in reactivities of the small and large basic proteins of the rat. Reciprocity of cross-reactivities among basic proteins was inconstant. 4. This study demonstrates the range of immunochemical cross-reactivities among myelin basic proteins and the sensitivity of quantitative microcomplement fixation in assessing such antigenic or conformational differences.

Freeze-fracture properties of central myelin in the bullfrog

The freeze-fractured membrane of the central myelin sheath has three classes of particulate components: (i) Particles inherent to the compact myelin lamellae. These are distributed at random and cleave predominantly with the P (protoplasmic) face. (ii) Particles which comprise the intramyelinic tight junctions. These are arranged in strands and are located at the inner and outer mesaxon, the paranodal loops, the cytoplasmic incisures, and occasionally within the compact regions of the myelin sheath. (iii) Particles localized exclusively at the portion of the paranodal loop membrane involved in the septate-like junction with the axolemma. These are regularly spaced and are organized in parallel rows. In the central myelin sheaths of bullfrogs fixed by perfusion with aldehydes and cryoprotected in 30% glycerol, the randomly distributed particles differ in size and shape from those of the axolemma. They possess a reasonably well defined bimodal distribution with respect to particle shape--most can be described either as globules or as ellipsoids. The globular particles range in diameter from 60 to 150 A. The ellipsoidal particles are 100-200 A long and 15-50 A wide. The total number of particles per square micron on the P face is approximately 1500. About half of these are of the globular type and half of the ellipsoidal type. In poorly fixed specimens, loss of interlamellar adhesion and loss of randomly distributed particles seem to coincide. Evidence is presented against the hypothesis that the tight junctions between compact myelin lamellae represent the radial component of the myelin. The possible relation between the types of particulate components seen in freeze-fracture and the classes of protein isolated from central myelin fractions is briefly discussed.

Large peptides of bovine and guinea pig myelin basic proteins produced by limited peptic hydrolysis

Bovine and guinea pig myelin basic proteins were cleaved with pepsin at pH 3.0 or pH 6.0 (enzyme/substrate, 1:500, w/w), and the peptides were isolated and identified. At pH 3.0 cleavage of the bovine protein occurred principally at three sites: Phe-Phe (88-89), Phe-Phe (42-43), and Leu-Asp (36-37). Minor cleavages occurred at Leu-Ser (110-111), Phe-Ser (113-114), and Ile-Phe (152-153). A study of the time course of the hydrolysis showed that the reaction was biphasic; nearly all of the protein was cleaved at Phe-Phe (88-89) before significant cleavages at other sites occurred. At pH 6.0 cleavage of the bovine protein occurred almost exclusively at a single site, the Phe-Phe bond at position 88-89, resulting in bisection of the protein. Treatment of the guinea pig protein with pepsin under the same conditions resulted in the production of peptides which were identical with those of the bovine protein in chromatographic and electrophoretic properties and in N-terminal and C-terminal residues but which differed slightly in amino acid composition.