Identification and characterization of citrulline-modified brain proteins by combining HCD and CID fragmentation

Citrullination is a protein PTM of arginine residues catalyzed by peptidylarginine deiminase. Protein citrullination has been detected in the CNS and associated with a number of neurological diseases. However, identifying citrullinated proteins from complex mixtures and pinpointing citrullinated residues have been limited. Using RP LC and high-resolution MS, this study determined in vitro citrullination sites of glial fibrillary acid protein (GFAP), neurogranin (NRGN/RC3), and myelin basic protein (MBP) and in vivo sites in brain protein extract. Human GFAP has five endogenous citrullination sites, R30, R36, R270, R406, and R416, and MBP has 14 in vivo citrullination sites. Human NRGN/RC3 was found citrullinated at residue R68. The sequence of citrullinated peptides and citrullination sites were confirmed from peptides identified in trypsin, Lys-C, and Glu-C digests. The relative ratio of citrullination was estimated by simultaneous identification of citrullinated and unmodified peptides from Alzheimer's and control brain samples. The site occupancy of citrullination at the residue R68 of NRGN ranged from 1.6 to 9.5%. Compared to CID, higher-energy collisional dissociation (HCD) mainly produced protein backbone fragmentation for citrullinated peptides. CID-triggered HCD fragmentation is an optimal approach for the identification of citrullinated peptides in complex protein digests.

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.

Expression of recombinant forms of human 21.5 kDa myelin basic protein and proteolipid protein in CHO cells

MBP and PLP are major structural protein components of myelin. Both proteins play a functional role in formation of myelin sheath and in maintenance of its compaction. Immune responses to MBP and PLP have been implicated in the pathogenesis of multiple sclerosis (MS), an auto-immune disease of the central nervous system. Recombinant forms of both proteins isolated and purified from bacterial or insect cell systems are commonly used to study the specificity of auto-response in MS. We have prepared recombinant forms of MBP and PLP stably expressed in CHO cells. Several clones with proper cytoplasmic MBP or surface PLP localization were obtained and characterized by flow cytometry and indirect immunostaining. CHO cells expressing the recombinant forms of MBP and PLP can be very useful in studies on the autoimmune mechanism of MS.

Identification of 4-hydroxy-2-nonenal-modified peptides within unfractionated digests using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The lipid peroxidation product 4-hydroxy-2-nonenal (HNE) is generated as a consequence of oxidative stress and can readily react with nucleophilic sites of proteins (e.g., histidine residues), mainly via a Michael addition. The formation of such lipid-protein conjugates can alter protein properties and biological functions, thus leading to highly deleterious effects. The present work describes a rapid (very limited sample preparation) and sensitive (low-femtomole range) procedure to identify HNE-modified peptides (Michael adducts) within unfractionated tryptic digests. The protocol involves the formation of dinitrophenylhydrazones of the Michael adducts, when using 2,4-dinitrophenylhydrazine as reactive matrix, followed by analysis using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The hydrazone derivatives present high desorption/ionization yield and can thus be preferentially detected compared to unmodified peptides. The MALDI mass spectrum obtained is therefore drastically different from the one obtained with the classical 4-hydroxy-alpha-cyanocinnamic acid matrix. Moreover, the presence of HNE, or more generally speaking carbonylated peptides, could be highlighted by 180 mass units differences (corresponding to the dinitrophenylhydrazone moiety) between these two MALDI mass spectra. Further information (e.g., localization/identification of the modified residues, peptide sequences) could be obtained by performing MALDI postsource decay (or electrospray) MS/MS experiments on the ions of interest.

Multiple sclerosis: an important role for post-translational modifications of myelin basic protein in pathogenesis

Myelin basic protein (MBP) represents a candidate autoantigen in multiple sclerosis (MS). We isolated MBP from normal and MS human white matter and purified six components (charge isomers) to compare the post-translational modifications on each. The sites and extent of methylation, deimination, and phosphorylation were documented for all tryptic peptides by mass spectrometry. We found that mono and dimethylated arginine 107 was increased in MS samples; deimination of arginine occurred at a number of sites and was elevated in MS; phosphorylation was observed in 10 peptides in normal samples but was greatly reduced or absent in most peptides from MS samples. Data obtained with MBP isolated from fresh brain obtained from a spontaneously demyelinating mouse model supported the view that the changes observed in human brain were probably related to pathogenesis of demyelination, i.e. we found decreased phosphorylation and decreased amounts of glycogen synthesis kinase in brain homogenates using specific antibodies. This study represents the first to define post-translational modifications in demyelinating disease and suggest an important role in pathogenesis.

Interactions of the 18.5-kDa isoform of myelin basic protein with Ca(2+)-calmodulin: in vitro studies using fluorescence microscopy and spectroscopy

The interactions of the 18.5-kDa isoform of myelin basic protein (MBP) with calmodulin (CaM) in vitro have been investigated using fluorescence microscopy and spectroscopy. Two forms of MBP were used: the natural bovine C1 charge isomer (bMBP/C1) and a hexahistidine-tagged recombinant murine product (rmMBP), with only minor differences in behaviour being observed. Fragments of each protein generated by digestion with cathepsin D (EC 3.4.23.5) were also evaluated. Using fluorescence microscopy, it was shown that MBP and CaM interacted in the presence of Ca2+ under a variety of conditions, including high urea and salt concentrations, indicating that the interaction was specific and not merely electrostatic in nature. Using cathepsin D digestion fragments of MBP, it was further shown that the carboxyl-terminal domain of MBP interacted with Ca(2+)-CaM, consistent with our theoretical prediction. Spectroscopy of the intrinsic fluorescence of the sole Trp residue of MBP showed that binding was cooperative in nature. The dissociation constants for formation of a 1:1 MBP-Ca(2+)-CaM complex were determined to be 2.1 +/- 0.1 and 2.0 +/- 0.2 microM for bMBP/C1 and rmMBP, respectively. Fluorescence spectroscopy using cathepsin D digestion fragments indicated also that the carboxyl-terminal region of each protein interacted with Ca(2+)-CaM, with dissociation constants of 1.8 +/- 0.2 and 2.8 +/- 0.9 microM for the bMBP/C1 and rmMBP fragments, respectively. These values show a roughly 1000-fold lower affinity of MBP for CaM than other CaM-binding peptides, such as myristoylated alanine-rich C-kinase substrate, that are involved in signal transduction.

Expression and properties of the recombinant murine Golli-myelin basic protein isoform J37

A recombinant form of the murine Golli-myelin basic protein (MBP) isoform J37 (rmJ37) has been expressed in Escherichia coli and isolated to 95% purity via metal chelation and ion exchange chromatography. The protein did not aggregate lipid vesicles containing acidic phospholipids, unlike the 18.5 kDa isoform of MBP. This result is consistent with J37 having a functional role prior to the assembly of compact myelin. Circular dichroic spectroscopy showed that rmJ37 had a large proportion of random coil in aqueous solution but gained alpha-helix and beta-sheet in the presence of monosialoganglioside G(M1) and PI(4)P. Thus, like "classic" MBP, J37 is intrinsically unstructured, and its conformation depends on its environment and bound ligands. Analyses of the amino acid sequence of rmJ37 predicted an N-terminal calmodulin (CaM)-binding site. It was determined via a gel-shift assay and fluorescence spectroscopy that rmJ37 and CaM interacted in a 1:1 ratio in a Ca(2+)-dependent manner. However, the interaction was weak compared with 18.5 kDa MBP.

An Arg/Lys-->Gln mutant of recombinant murine myelin basic protein as a mimic of the deiminated form implicated in multiple sclerosis

The degree of post-translational enzymatic deimination (conversion of arginyl to citrullinyl residues) of myelin basic protein (MBP) is correlated with the severity of the human autoimmune disease multiple sclerosis (MS). It is difficult to obtain large quantities of deiminated MBP from natural sources (autopsy material), and in vitro deimination using peptidylarginine deiminase (EC 3.5.3.15) is both non-specific and irreproducible. Since there is no known codon for citrulline, we have constructed a mutant form of recombinant murine MBP (rmMBP) in which 5 Arg and 1 Lys residues have been replaced by Gln as the most reasonable analogue of Cit. The residues were chosen to correspond to the 6 Arg residues in human MBP which are most commonly deiminated in chronic MS. The mutant species, rmMBP-qCit(6) where the "q" represents "quasi-," was probed by numerous biochemical and biophysical techniques. Highly homogeneous protein preparations were obtained using a modified expression system which minimised spurious misincorporation of Lys for Arg, as ascertained by electrospray ionisation mass spectrometry. The mutant form rmMBP-qCit(6) had a reduced ability to aggregate lipid vesicles, a slightly greater susceptibility to digestion by cathepsin D, a greater proportion of random secondary structure, and different conformational responses to lipids, compared with the unmodified rmMBP. Overall, the mutant protein's properties were consistent with the effects of deimination and support its use as a model for evaluating the effects of this modification.

Absence of chicken myelin basic protein residues in commercial formulations of MMR vaccine

Several preparations of MMR vaccines and their progenitor monovalent vaccine bulks produced by two different manufacturers were examined serologically for the presence of chicken myelin basic protein (MBP) residues. The products were challenged against several commercial preparations of anti-hMBP antisera that reacted positively with the control MBP preparations of human and chicken origins. There was no evidence of the presence of MBP components in MMR vaccines or their progenitor vaccine bulks as shown by the reactivity profiles of the antibody preparations against control and test antigens.

p-Cresol sulfate is the dominant component of urinary myelin basic protein like material

Multiple sclerosis (MS) is clinically heterogeneous and has an uncertain natural history. A high priority for more effective treatment of MS is an objective and feasible laboratory test for predicting the disease's course and response to treatments. Urinary myelin basic protein (MBP)-like material (MBPLM), so designated because it is immunoreactive as a cryptic epitope in peptide 83-89 of the human MBP molecule of 170 amino acids, is present in normal adults, remains normal in relapsing-remitting, but increases in progressive MS. In the present investigation, MBPLM was purified from urine and characterized. p-Cresol sulfate is the major component of urinary MBPLM. This conclusion is based on the following: (1) MBPLM and p-cresol sulfate both have a mass of 187 on negative scans by electrospray ionization mass spectrometry, the same fragments on tandem mass spectrometry of 80 (SO(-)(3)) and 107 (methylphenol), and similar profiles on multiple reaction monitoring; (2) (1)H and (13)C nuclear magnetic resonance spectroscopy revealed identical spectra for MBPLM and p-cresol sulfate; (3) purified p-cresol sulfate reacted in parallel with MBP peptide 83-89 in the same radioimmunoassay for MBPLM; and (4) p-cresol sulfate has the same behavior on preparative HPLC columns as urinary MBPLM. The unexpected immunochemical degeneracy permitting a cross-reaction between p-cresol sulfate and a peptide of an encephalitogenic myelin protein is postulated to be based on shared conformational features. The mechanisms by which urinary p-cresol sulfate, possibly derived from tyrosine-SO(4), reflects progressive worsening that is disabling in MS are unknown.

Purification of myelin basic protein from bovine brain

Myelin basic protein (MBP) is a commonly used substrate for in vitro determination of numerous protein kinase activities. Herein we describe a rapid method for isolating relatively large amounts of MBP from bovine brain with a purity greater than that currently available from commercial sources. Lipids were first extracted from the CNS tissue by homogenization in sec-butanol. Washes under neutral and mildly basic conditions were employed to remove neutral and acidic proteins from the defatted residue. MBP was subsequently extracted under acidic conditions and further purified by chromatography on CM Sephadex C-25. Potential contaminating enzyme activities were destroyed by heart treatment. This method typically yields a recovery of 1.0-1.5 mg MBP per gram of starting material with a purity of greater than 95%. The MBP prepared in this manner was suitable for determination of kinase activities by both solution and the "in gel" kinase assay systems.

A simple and rapid method for isolating myelin basic protein

The conduction of impulses along axons of nerves is facilitated by the myelin sheath, composed of proteins and lipid. Myelin basic proteins (MBPs) are extrinsic membrane proteins that play an important role in the structural organization of the myelin sheath. In the central nervous system, MBPs account for 30-40% of total protein. The traditional method of MBP isolation involves the use of chloroform-ethanol, which would destroy the native form of MBP. A modified method for maintaining its native form was developed. The white matter of porcine brain was directly extracted by buffers containing different concentrations of sodium chloride owing to MBP solubilized at high concentration of NaCl. The MBP was further purified by cation exchange chromatography and buffers containing glycine and salts. Purified MBP were consistently obtained by this method.

Conformation of bovine myelin basic protein purified with bound lipids

The basic protein of myelin (called MBP) is an extrinsic protein of the myelin membrane. Its structure and function are still unknown. MBP has been extensively studied in its water-soluble form, but it is also known in a detergent-soluble form, which is purified with endogenous myelin lipids and should correspond to the native form of the protein in the membrane. In order to acquire insight into the structure of MBP, we have carried out circular dichroism (CD) experiments on the protein both in the lipid-free and in the lipid-bound form. Our data clearly show that lipid-free MBP is mainly disordered with only a small amount having alpha-helix and beta-sheet motifs. On the other hand, the lipid-bound form of MBP appears to have a consistent amount of ordered secondary structure. Theoretical predictions, made using different computational methods, substantially confirm the tendency of the protein to assume an ordered secondary structure in accordance with our CD results.

Analysis of the membrane-interacting domains of myelin basic protein by hydrophobic photolabeling

Myelin basic protein is a water soluble membrane protein which interacts with acidic lipids through some type of hydrophobic interaction in addition to electrostatic interactions. Here we show that it can be labeled from within the lipid bilayer when bound to acidic lipids with the hydrophobic photolabel 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine (TID) and by two lipid photolabels. The latter included one with the reactive group near the apolar/polar interface and one with the reactive group linked to an acyl chain to position it deeper in the bilayer. The regions of the protein which interact hydrophobically with lipid to the greatest extent were determined by cleaving the TID-labeled myelin basic protein (MBP) with cathepsin D into peptides 1-43, 44-89, and 90-170. All three peptides from lipid-bound protein were labeled much more than peptides from the protein labeled in solution. However, the peptide labeling pattern was similar for both environments. The two peptides in the N-terminal half were labeled similarly and about twice as much as the C-terminal peptide indicating that the N-terminal half interacts hydrophobically with lipid more than the C-terminal half. MBP can be modified post-translationally in vivo, including by deamidation, which may alter its interactions with lipid. However, deamidation had no effect on the TID labeling of MBP or on the labeling pattern of the cathepsin D peptides. The site of deamidation has been reported to be in the C-terminal half, and its lack of effect on hydrophobic interactions of MBP with lipid are consistent with the conclusion that the N-terminal half interacts hydrophobically more than the C-terminal half. Since other studies of the interaction of isolated N-terminal and C-terminal peptides with lipid also indicate that the N-terminal half interacts hydrophobically with lipid more than the C-terminal half, these results from photolabeling of the intact protein suggest that the N-terminal half of the intact protein interacts with lipid in a similar way as the isolated peptide. The similar behavior of the intact protein to that of its isolated peptides suggests that when the purified protein binds to acidic lipids, it is in a conformation which allows both halves of the protein to interact independently with the lipid bilayer. That is, it does not form a hydrophobic domain made up from different parts of the protein.

Isolation of myelin basic protein-specific T cells predominantly from the memory T-cell compartment in multiple sclerosis

Myelin antigen-reactive T cells have been implicated in the pathogenesis of multiple sclerosis (MS). Myelin-reactive T cells can be isolated from control subjects as well as individuals who have MS. Experimental models of MS indicate that recently stimulated, myelin-reactive T cells have greater encephalitogenic potential than resting T cells. Activation induces changes in T-cell surface antigens that may distinguish previously stimulated, memory T cells from naive T cells. Therefore, we examined 108 myelin basic protein (MBP)-reactive T-cell lines from 7 MS and 8 control subjects to determine whether MBP-reactive T cells originated in the memory T-cell subset or in the naive subset. Isotypes of CD45 were used that designate memory or naive T cells. In subjects having MS, 84% of the MBP-reactive T cells resided in the memory T-cell subset. However, in control subjects, only 13% of MBP-specific T cells originated from the memory T-cell subset. This result suggests that a substantial proportion of MBP-reactive T cells from some individuals with MS have been previously activated in vivo. This difference provides additional support for the hypothesis that myelin antigen-specific T cells are involved in the pathogenesis of MS.

Expression and crystallization of the complex of HLA-DR2 (DRA, DRB1*1501) and an immunodominant peptide of human myelin basic protein

HLA-DR2 is associated with susceptibility to multiple sclerosis (MS). A peptide from human myelin basic protein (MBP, residues 85-99) was previously found to bind to purified HLA-DR2 (DRA, DRB1*1501) and to be recognized by human MBP-specific T cell clones. Soluble HLA-DR2 was expressed in the baculovirus system by replacing the hydrophobic transmembrane regions and cytoplasmic segments of DRalpha and DRbeta with leucine zipper dimerization domains from the transcription factors Fos and Jun. In the expression construct, the MBP(85-99) sequence was covalently linked to the N terminus of the mature DRbeta chain. The recombinant protein was secreted by Sf9 cells infected with the recombinant baculovirus and purified by affinity chromatography. The leucine zipper dimerization domains were then cleaved from the assembled HLA-DR2/MBP peptide complex with V8 protease, and the protein was further purified by anion-exchange HPLC. Analysis by HPLC gel filtration indicated that the HLA-DR2/MBP peptide complex did not have a tendency to aggregate. The purified HLA-DR2/MBP peptide complex readily crystallized by the hanging drop method in 15-18% polyethylene glycol 6000/100 mM glycine, pH 3.5. At a synchrotron radiation source, a crystal with a tetragonal space group diffracted to a resolution of 2.6 A. The expression of such homogenous HLA-DR/peptide complexes may facilitate cocrystallization with T cell receptors as well as other molecules involved in T cell receptor recognition and signaling.

Weak binding and removal of extrinsic proteinase activities of myelin membranes

The concurrent release of myelin basic protein (MBP) and extrinsic proteinases from isolated myelin membranes by aqueous solvents of high ionic strength is considered circumstantial evidence of a presumptive mutual interaction in situ. The joint release of proteins and proteinases from myelin membranes of bovine brain, depending on the ionic strength of aqueous solvents, was therefore examined; 25 mM Tris buffer released an average 1.4% of total myelin protein. It was attributable to about 25 different electrophoretic bands, but no apparent MBP. However, the extract potently mediated the limited proteolysis of added MBP at pH 4.0, 5.6, and 9.0. Because of the pH and the effects of specific inhibitors, proteolysis appears to be owing to activities of cathepsin B and D, and an alkaline metalloproteinase. The subsequent extraction of myelin membranes with buffered 300 mM NaCl released an additional 20% of total myelin protein, mainly MBP. The extracts, unlike those of untreated myelin membranes, no longer cleaved MBP at pH 5.6 and 9.0, and did so only slightly at pH 4.0. The results indicate that the bulk of soluble myelin-associated proteinases is much less tightly bound than MBP. The weak binding of the former and the prevalence of lysosomal cathepsin B- and D-like activities suggest that during their isolation, myelin membranes may adsorb soluble cellular proteins of tissue homogenates. At any rate the washing of myelin membranes with dilute buffer was found to largely remove soluble proteinase activities that are otherwise associated with salt-soluble MBP of myelin.

Isolation of myelin basic protein from whole tissue extracts by selective pH-dependent solubilization

A previous study of the selective solubility of myelin basic protein (MBP) of tissue extracts at pH 9.0 has raised issues of its quantitative recovery, and the differential solubility of its charge isomers. The pH-dependent solubility of proteins of acid extracts of delipidated tissue of bovine spinal cord was therefore reexamined. MBP of whole extracts was completely soluble up to pH 8.0 only, and less so by 25% at pH 9.0, and 43% at pH 10.0. The proteins other than MBP were virtually insoluble between pH 5.0 to 6.0, and 9.0 to 10.0. The solubility of the main charge isomers I to III of MBP of 18.5 kDa was found not to be affected by pH. Either pH 5.0 or 9.0 is therefore suitable for the selective isolation of MBP from whole tissue extracts, only pH 5.0 providing for the complete recovery of MBP. The pH-dependent solution behaviour was also examined following the separation of proteins of whole extracts by anion exchange chromatography at pH 10.4. Purified MBP and several related minor cationic components of lower molecular weight were soluble throughout. In contrast, the anionic proteins were only partly soluble between pH 4.0 to 10.0, i.e. by 4 to 20%. The results are consistent with specific protein-protein interactions of the proteins of whole extracts, either enhancing the solubility of non-MBP proteins, e.g. at pH 7.0, or impairing that of MBP between pH 8.0 to 10.0.

Characterization of myelin basic protein charge microheterogeneity in developing mouse brain and in the transgenic shiverer mutant

Myelin basic protein (MBP) is a highly heterogeneous family of membrane proteins consisting of several isoforms resulting from alternative splicing and charge isomers arising from posttranslational modifications. Although well characterized in the bovine and human species, those in the mouse are not. With the availability of a number of transgenic and knockout mice, the need to understand the chemical nature of the MBPs has become very important. To isolate and characterize the MBP species in murine brain, two methods were adapted for use with the small amounts of MBP available from mice. The first was a scaled-down version of the preparative CM-52 chromatographic system commonly used to isolate MBP charge isomers; the second was an alkaline-urea slab gel technique that required five times less material than the conventional tube gel system and, from these gels, western blots were readily obtained. Murine MBP was resolved into two populations of charge isomers: the 18.5- and 14-kDa isoforms. Isolation and characterization of these charge isomers or components permitted us to assign possible posttranslational modifications to some of them. Component 1 (C-1), the most cationic isomer, had a molecular weight of 14,140.38 +/- 0.79. C-2 consisted of two 14-kDa species, 14,136.37 +/- 0.74 and 14,204.45 +/- 0.70. Two variants, 14,215.57 +/- 0.94 and 18,413.57 +/- 0.76, constituted C-3. C-4, C-5, and C-8 (the least cationic isomer) each consisted of both 14- and 18.5-kDa isoforms. During myelinogenesis, the 18.5-kDa isoform appeared first (day 4); the 14-kDa isoform appeared at day 16 and subsequently became the dominant isoform. The transgenic shiverer mutant synthesized mainly the 18.5-kDa isoform, but none of the 14-kDa isoform, similar to the 4-day-old mouse. We concluded that the transgenic shiverer was able to initiate myelinogenesis with the 18.5-kDa isoform, but was unable to complete myelinogenesis because of the absence of the 14-kDa isoform.

Detection of myelin basic protein isoforms by organic concentration

An effective technique was developed, which allowed rapid isolation of highly pure myelin basic protein (MBP) including its distinct isoforms. The procedure employs homogenization of central nervous system (CNS) tissue in chloroform, which specifically extracts MBP. Subsequently, methanol was used to convert the protein susceptible to quantitative transfer into the acidic aqueous phase. MBP was purified from bovine, chicken, fish, human, guinea-pig, mouse, rabbit, rat, and swine brains. Analysis on SDS-PAGE and immunoblotting using polyclonal MBP-specific serum recognized proteins corresponding to the sizes of previously identified MBP isoforms of 21.5, 18.5, 17.2, and 14.2 kDa and three predicted isoforms of 20.2, 16.0, and 13 kDa. The MBP obtained was readily soluble in water and possessed the capacity to induce experimental autoimmune encephalomyelitis in susceptible mice. The protein was also suitable for use as a substrate for protein kinases.

Increased expression of protein kinase C beta activates ERK3

In a prior study, we have shown that stable transfection of expression plasmids for protein kinases C beta 1 (PKC beta 1) or PKC beta 2 into differentiated colon cancer cells led to elevated levels of PKC beta 1 or PKC beta 2 protein and PKC beta kinase activities in the transfectants, without altering PKC alpha levels. PKC gamma is not found in these cells, so the major modulation was in PKC beta. PKC beta transfectant cells exhibited blocked differentiation, increased growth rate in athymic mice, and restoration of the basic fibroblast growth factor response pathway. In this study, we have extended the analysis of these PKC beta transfectants to the mitogen-activated protein kinase ERK3. Analysis of cell lysates on the mitogen-activated protein kinase substrate myelin basic protein by in gel kinase assay showed increased activity at 63 kDa, the size of ERK3, in each of two PKC beta 1 and each of two PKC beta 2 transfectants compared with the vector control transfectant. ERK3 was expressed at equal abundance in PKC beta 1, PKC beta 2, and control transfectant cells as demonstrated by Western blotting and by immunoprecipitation with anti-ERK3 monoclonal antibody. However, a > 10-fold increase in ERK3 activity in each PKC beta transfectant was shown by immunoprecipitation with anti-ERK3 monoclonal antibody followed by either immune complex kinase assay or by in gel kinase assay. Thus, while overexpression of transfected PKC beta does not lead to overexpression of ERK3, it does lead to constitutive activation of ERK3. A causal link between PKC beta overexpression and ERK3 activation was established because 12-O-tetradecanoylphorbol-13-acetate treatment down-regulated both PKC and ERK3 activities in both PKC beta 1 transfectants. ERK3 activity was found in nuclear and membrane fractions in each PKC beta transfectant, in contrast to controls, perhaps accounting for constitutive activation of ERK3 in cells with elevated levels of PKC beta 1 or PKC beta 2.

[Ability of a recombinant protein containing fragment 114-122 of myelin basic protein, to cause allergic encephalomyelitis in guinea pigs]

Four genetic constructions have been designed, capable of producing in E. coli the hybrid beta-galactosidases containing the encephalitogenic determinant 114-122 of myelin basic protein. The ability of chromatography-purified proteins to cause allergic encephalomyelitis in guinea pigs has been investigated. Only one out of four proteins carrying at least one complete replica of encephalitogenic determinant did induce allergic encephalomyelitis in animals. Effects of the structural context of the encephalitogenic determinant on its functional activity are discussed.

Purification of a new clathrin assembly protein from bovine brain coated vesicles and its identification as myelin basic protein

The multimeric clathrin assembly proteins AP-1 and AP-2 with molecular masses of approximately 270 kDa and the monomeric clathrin assembly proteins AP180 and auxilin with molecular masses of approximately 90 kDa catalyze the assembly of clathrin into artificial clathrin baskets under physiological conditions. We have now identified a much smaller approximately 20-kDa clathrin assembly protein in 0.5 M Tris, pH 7.0, extracts of bovine-brain coated vesicles and purified it to near homogeneity. A polyclonal antibody against this protein did not cross-react with any of the other assembly proteins, and sequencing data suggest that this new protein is similar or identical to myelin basic protein (MBP). At a molar ratio of 3 molecules per clathrin triskelion, MBP catalyzes polymerization of clathrin into artificial baskets that appear structurally similar to the baskets assembled by the other assembly proteins. In addition, like the other baskets, the clathrin-MBP baskets are uncoated by hsp70. MBP represents a significant fraction of the total assembly protein activity present in 0.5 M Tris, pH 7.0, extracts of coated vesicles. It is not clear if it acts as an assembly protein in vivo, but because it is well characterized and easily available, MBP will be a useful protein to investigate the mechanism of clathrin assembly and disassembly in vitro.

Purification of immunologically active recombinant 21.5 kDa isoform of human myelin basic protein

We have designed and expressed in bacteria a recombinant fetal form of human myelin basic protein (21.5 kDa isoform; rhMBP21.5), a candidate autoantigen in multiple sclerosis. An exon 2 insertion, carboxy-terminal histidine tag and preferred bacterial codons differentiate the MBP21.5 gene from that encoding the adult, brain-derived form of human MBP (18.5 kDa isoform; hMBP18.5). MBPs were expressed at high levels in E. coli and extracted from whole cells by simultaneous acid solubilization and mechanical disruption. A nearly two-fold increase in recombinant protein was detected in strains harboring MBP genes with bacterial preferred codons compared to genes containing human codons. The recombinant molecules were purified in two steps, first by reversed-phase chromatographic separation and then by metal affinity chromatography. Dimeric forms of recombinant MBP21.5 were detected under physiological conditions, however, substitution of a serine for the single cysteine at amino acid residue 81 resulted in only monomer formation. All forms of recombinant MBPs induced proliferative responses of human T lymphocytes specific for epitopes in MBP18.5 kDa. In contrast, human T cell lines that recognize an exon 2-encoded epitope of MBP responded to the 21.5 kDa isoform of MBP, but not the 18.5 kDa isoform.

Extracellular Ca2+ stimulates the activation of mitogen-activated protein kinase and cell growth in human fibroblasts

In serum-free medium containing serum replacements but totally lacking in protein growth factors, diploid human fibroblasts remained quiescent if the extracellular Ca2+ concentration was only 0.1 mM. However, when the Ca2+ concentration in this medium was increased to 1 mM, the cells replicated as rapidly as they do in medium supplemented with protein growth factors. When quiescent cells in medium with only 0.1 mM Ca2+ were exposed to 1 or 10 mM Ca2+ or 100 ng/ml epidermal growth factor (EGF), the 42 kDa and 44 kDa forms of mitogen-activated protein kinase (MAPK) were rapidly activated, as demonstrated by a characteristic electrophoretic mobility shift of these proteins and by their enhanced ability to phosphorylate myelin basic protein (MBP). Analysis of fractions from Mono Q anion-exchange chromatography of lysates of cells exposed to 10 mM Ca2+ or 100 ng/ml EGF revealed a peak of MBP phosphorylation activity that was coeluted with p42 and p44 MAPK as shown by immunoblot analysis. Activation of MAPK by extracellular Ca2+ was dose-dependent and biphasic, with a peak of activation at 5-10 min after exposure, followed by a period of sustained activation of MAPK at a lower level. This pattern has been shown [Vouret-Craviari, Van Obberghen-Schilling, Scimeca, Van Obberghen and Pouysségur (1993) Biochem J. 289, 209-214] to correlate with the re-entry of mammalian cells into the cell cycle.

The isolation and characterization of four myelin basic proteins from the unbound fraction during CM52 chromatography

The unbound fraction from CM52 columns was used as the source of at least four additional myelin basic protein (MBP) molecules. From this fraction we routinely obtained two major fractions called C8-A and C8-B. The C8-A and C8-B fractions were further purified on HPLC. Each contained two proteins in the 17- to 18-kDa range which we called C8-A(H) (higher M(r)), C8-A(L) (lower M(r)), C8-B(H), and C8-B(L). The citrulline values (calculated as citrulline plus ornithine) were high in three of the four proteins, which was accompanied by a compensatory decrease in the arginine values. The compositions clearly identified these four proteins with the citrullinated form of MBP. Western blot analysis showed that both H and L forms reacted with anti MBP antibodies. Partial sequence analysis after cyanogen bromide cleavage, showed that the sequences of both proteins in the C8-B fraction (C8-B(H) and C8-B(L)) were identical to the 18.5-kDa isoform of MBP. Mass spectrometry by electrospray ionization of the C8-B(H) and C8-B(L) provided us with accurate masses of 18,558.08 +/- 8.13 and 17,266.63 +/- 2.24, respectively. We concluded that the H and L proteins from the C8-B fractions were MBPs. Although similar detailed analyses of the C8-A(H) and C8-A(L) have not been done they are also considered to be MBP on the basis of the immunoreactivity with anti MBP antibodies. The origins of these proteins is not known at this time and their functional significance is obscure. The possibility that they are found in early forms of myelin, as components of transitional membranes between oligodendrocytes and myelin or are involved in remyelination, cannot be discounted.

Myelin basic protein purified on an ion-exchange continuous polymer bed in the presence of ethylene glycol and salt possesses activity against p-nitrophenyl acetate

In this paper we describe a fast and mild method based on the use of a unique cation exchanger and buffers containing ethylene glycol and salt for the purification of the myelin basic protein (MBP; MW 18.5 kDa). MBP thus purified hydrolyses catalytically p-nitrophenyl acetate. This esterase activity facilitates not only the purification of MBP but also indicates that probably it is in its native state, i.e. there is a good chance that the purified molecules are structurally and chemically identical. This is a prerequisite to obtain crystals appropriate for x-ray diffraction and other studies.

Epidermal growth factor stimulates mitogen-activated protein kinase by a PKC-dependent pathway in human keratinocytes

Epidermal growth factor (EGF), 20 ng/ml, stimulated myelin basic protein (MBP) phosphorylation in crude extracts from human keratinocyte primary cultures. In order to identify the involved kinases, we separated by fast protein liquid chromatography proteins participating in MBP phosphorylation. We detected three MBP kinase activities in the keratinocyte crude extracts. The first MBP kinase activity was the only one stimulated by EGF and reacted with anti-mitogen-activated protein kinase (MAPK) antiserum recognising p42mapk and p44mapk isoforms. However, when protein kinase C (PKC) was either inhibited by the PKC inhibitor GF 109203X or depleted by a prolonged TPA treatment, the stimulation of MBP phosphorylation by EGF was strongly inhibited. The second MBP kinase activity eluted was due to a PKC isoform reacting with an anti-PKC zeta antibody, and the third was not identified. With this work, we have thus shown that, in human keratinocytes, EGF activates MAPK activity by a PKC-dependent pathway.

Reactivity of normal T-cell lines to MBP isolated from normal and multiple sclerosis white matter

T-cell reactivity to human myelin basic protein (MBP) has been extensively studied using T-cell lines and clones generated from both peripheral blood and cerebrospinal fluid, from normal controls and multiple sclerosis (MS) patients. These studies have largely utilized myelin basic protein isolated from control human adult white matter. In our study, we used MBP reactive T-cell lines as a probe to investigate antigenic differences in a series of MBP preparations isolated from either control human white matter or white matter from the central nervous system (CNS) of MS patients. Autologous peripheral blood derived mononuclear cells were used as antigen presenting cells (APC). Although the majority of T-cells were found to react equally well with all preparations of MBP isolated from both control and MS white matter, we were also able to identify T-cell lines which reacted well with all preparations of MBP isolated from controls but failed to react with MBP isolated from MS white matter. These differences were unlikely to reflect differences in degradation products or excess peptides present in the MS brain since SDS-PAGE and HPLC did not show any difference in the MS samples compared to the controls, and the concentration response curves for a human T-cell clone specific for the 84-102 region of MBP were similar for all the MBP preparations. We did not detect differences in amino acid content amongst MBP preparations although single amino acid substitutions cannot be ruled out. These results raise the possibility that MBP isolated from MS brain may differ in charge microheterogeneity which would affect antigenic determinants.(ABSTRACT TRUNCATED AT 250 WORDS)

Human T lymphocytes distinguish bovine from human P2 peripheral myelin protein: implications for immunological studies on inflammatory demyelinating neuropathies

In patients with inflammatory demyelinating neuropathy, which is possibly mediated by autoreactive, myelin-specific T lymphocytes, most studies focusing on immune responses to the major neuritogenic myelin protein P2 have been performed with bovine P2. However, the primary structure of bovine P2 differs from the human protein by nine amino acid residues that may profoundly influence the antigen recognition by T lymphocytes. We purified bovine and human P2 from peripheral nervous tissue and established a total of 19 T cell lines (TCL) reactive with bovine P2 from blood of two patients with acute Guillain-Barré syndrome (n = 5 TCL) and from six healthy individuals. Only four of these TCL, all raised from the blood of the GBS patients, transiently cross-recognized human P2 protein. Our results suggest that the use of human autoantigen may be crucial for the characterization of T cellular immune responses against P2 protein both in patients with inflammatory demyelinating neuropathy and in healthy controls.

Separation of complexes of major histocompatibility class II molecules and known antigenic peptide by metal chelate affinity chromatography

A small fraction of affinity-purified MHC class II molecules are known to bind antigenic peptides in vitro. No simple method with acceptable recovery exists for separation of complexes of a known antigenic epitope and MHC class II from empty MHC class II and complexes of MHC class II and endogenously bound peptide. Here we describe an one step metal chelate affinity chromatography method to purify complexes of MHC class II and antigenic peptide of known composition. Complexes of human HLA-DR2 (DRB1*1501/DRB5*0101) and a peptide analog from human myelin basic protein MBP(84-102) containing a 6 histidine tag (6 x His) and a tyrosine residue at the N-terminus end [6 x His-MBP(83-102)Y83] were prepared and purified. The absence of residual free 6 x His-MBP peptide in the complex preparations were confirmed by gel filtration and TLC analyses. The purified complexes were applied onto Ni2+.nitrilotriacetic acid (Ni2+.NTA)-agarose affinity support and 6 x His-tagged peptide class II complexes were selectively eluted with imidazole-containing buffer. The quantitation of bound peptide in the eluted complexes showed 100% occupancy of HLA-DR2 (DRB1*1501/DRB5*0101) with [6 x His-MBP(83-102)Y83] peptide with a recovery of 50-75%. The presence of a single peptide entity in the eluted complexes was confirmed by reverse-phase narrowbore HPLC analysis of the acid-extracted supernatant and by amino acid sequencing analyses. As expected, no endogenous polypeptide was detected in the Ni2+.NTA eluted complexes when analyzed by two-dimensional IEF gel electrophoresis. Finally, we demonstrate that both MBP(84-102) and [6 x His-MBP(83-102)Y83] peptides were equally capable of stimulating restricted T cell line in the presence of autologous antigen presenting cells (APCs). These results demonstrate that metal chelate affinity chromatography can be used to prepare MHC class II-peptide complexes containing single peptide. Such complexes of class II molecules containing known peptide have significant clinical relevance for antigen-specific therapy of various autoimmune diseases and may provide better understanding of the trimolecular interaction between MHC class II, antigenic peptide and T cell receptor (TCR).

Involvement of protein kinase C during activation of the mitogen-activated protein kinase cascade by leukemia inhibitory factor. Evidence for participation of multiple signaling pathways

We show here that treatment of 3T3-L1 cells with leukemia inhibitory factor (LIF) stimulates the activation of mitogen-activated protein kinase kinase (MAPKK), mitogen-activated protein kinase (MAPK), and S6 protein kinase (S6K) activities both in a time- and dose-dependent manner. A single peak of MAPKK activity, four peaks of activity against the S6 synthetic peptide, RRLSSLRA (S6 peptide), and three distinct peaks toward myelin basic protein (MBP) were observed after Mono-Q chromatography of LIF-stimulated cell extracts. Two of the MBP kinase activities correlated with the stimulation of extracellular signal-regulated kinases 1 and 2. Interestingly, down-regulation of protein kinase C (PKC) by chronic treatment of 3T3-L1 cells with phorbol ester was found to attenuate, but not block, the LIF-mediated stimulation of MAPKK, MAPK, and S6K activities in 3T3-L1 cells. Treatment of 3T3-L1 cells with epidermal growth factor increased MAPKK, MAPK, and S6K activities to a similar extent as LIF, but this activation was not attenuated by down-regulation of PKC. Our results suggest that the full activation of the MAPK cascade by LIF may require inputs from multiple signaling pathways, one of which is dependent upon the presence of functional PKC.

Fractionation of central nervous system myelin proteins by reversed-phase high-performance liquid chromatography

Chromatographic fractionation of central nervous system myelin proteins is hampered by their poor solubility in water and strong association with lipids. Moreover, several myelin membrane proteins undergo posttranslational acylation which further increases their hydrophobicity. Here, a method is described for a two-step delipidation and high-resolution fractionation by reversed-phase high-performance liquid chromatography of all myelin proteins. The elution was monitored of the two major protein components, i.e. myelin basic protein (MBP) and proteolipid protein (PLP), as well as of minor components, viz. myelin-associated glycoprotein (MAG) and myelin/oligodendrocyte glycoprotein (MOG). Whereas MBP and MOG elute as single sharp protein peaks upon chromatography, PLP and MAG are resolved into several different components. Following their delipidation and separation, all proteins including the hydrophobic transmembrane proteins can be transferred to fully aqueous solutions without detergents. The overall yield of myelin proteins obtained in this way exceeds 85%.

Inhibition of myelin formation by HIV-1 gp120 in rat cerebral cortex culture

To study the role of HIV-1 gp120 in loss of myelin in HIV encephalopathy, the binding of gp120 to various types of neural cells and its effects on myelination were examined in rat primary brain culture. Double-staining of cultured cells with gp120 and specific antibodies for different neural cell types showed that gp120 bound to most of the galactocerebroside (GalC)-positive oligodendrocytes, a small population of type-2-like astrocytes and a few small neurons. Gp120 did not bind to type-1-like astrocytes, most neurons, or to macrophage/microglia. To assay myelination, cells were bathed in a myelination medium containing chick embryo extract and high glucose, with or without gp120. Seven days after the application, myelination in the culture was observed morphologically and by staining with anti-myelin basic protein (MBP) antibody, and was found to be significantly inhibited by the addition of gp120 (50-100 nM). The processes of oligodendrocytes were reduced in length and arborization relative to the control, but MBP production by oligodendrocytes was unaffected. These results show that gp120 can cause a functional disorder of oligodendrocytes and thus could underlie the diffuse loss of myelin sheaths of HIV encephalopathy.

A new detergent to purify CNS myelin basic protein isoforms in lipid-bound form

We have previously shown that CNS myelin basic protein (MBP) can be purified in the lipid-bound, native-like form by using a procedure based on myelin solubilization with detergents at pH above 7, and on the filter-like use of hydroxyapatite to separate non-adsorbed MBP from other myelin proteins. Here, we report on the isolation of MBP in the zwitterionic detergent 3-((3-cholamidopropyl)dimethylammonio)-1-propane sulfonate (CHAPS), which does not interfere at 280 nm and can be removed by dialysis. This detergent appears to improve MBP purification and to be suitable for fluorescence and reconstitution studies that can be useful to understand both structure and function of MBP in its natural environment.

Fragmentation of phospholipid bilayers by myelin basic protein

Human myelin basic protein (MBP) is shown to disrupt multilamellar phosphatidylcholine bilayers into small lipoprotein particles in a manner similar to the cytolytic peptide melittin (Dufourc, E. J., Smith, I. C. P., & Dufourcq, J. (1986) Biochemistry 25, 6448-6455). This bilayer fragmentation, as monitored by 31P nuclear magnetic resonance, is temperature-dependent and completely inhibited by the presence of small amounts of negatively charged phosphatidylserine. The stabilizing property of phosphatidylserine is lost with the neutralization of its negative charges upon membrane binding of cationic species such as calcium ions. No MBP-induced fragmentation is observed with bilayers of negative or zwitterionic lipid mixtures which mimic the myelin lipid composition. The membrane fragmentation observed in vitro in the presence of MBP could play a role in vivo in demyelinating diseases.

Defective CD3 mediated proliferation and LPS responsiveness in multiple sclerosis

Multiple sclerosis [MS] is a chronic inflammatory disease of the central nervous system which has been postulated to be a T cell mediated disease. We examined proliferation of mononuclear cells to OKT3 mAb, Con A, ionomycin plus PMA and human myelin basic protein in subjects with relapsing-remitting and chronic progressive multiple sclerosis. Age and sex matched controls demonstrated a good proliferation to anti-CD3 mAb whereas subjects with relapsing-remitting multiple sclerosis showed a significantly decreased anti-CD3 mAb response. There was no difference in mitogen, ionomycin plus PMA or human MBP proliferation between controls and MS subjects. There was also a trend for decreasing anti-CD3 mAb proliferation in patients with chronic progressive multiple sclerosis compared to controls. LPS significantly decreased anti-CD3 mAb proliferation in controls but not in the MS subjects. An abnormality of signal transduction via the CD3 T-cell receptor complex in T cells and responsiveness to the immunomodulatory effect of IFN inducers may exist in multiple sclerosis.

Myelin basic protein-specific T lymphocyte repertoire in multiple sclerosis. Complexity of the response and dominance of nested epitopes due to recruitment of multiple T cell clones

The human T cell response to the myelin basic protein (MBP) has been studied with respect to T cell receptor (TCR) usage, HLA class II restriction elements, and epitope specificity using a total of 215 long-term MBP-specific T cell lines (TCL) isolated from the peripheral blood of 13 patients with multiple sclerosis (MS) and 10 healthy donors. In most donors, the anti-MBP response was exceedingly heterogeneous. Using a panel of overlapping synthetic peptides spanning the entire length of human MBP, at least 26 epitopes recognized by human TCL could be distinguished. The MBP domain most commonly recognized was sequence 80-105 (31% of MS TCL, and 24% of control TCL). Sequence 29-48 was recognized more frequently by control-derived TCL (24%) than by TCL from MS patients (5%). The MBP epitopes were recognized in the context of DRB1 *0101, DRB5*0101, DRB1*1501, DRB1*0301, DRB1*0401, DRB1*1402, and DRB3*0102, as demonstrated using a panel of DR gene-transfected L cells. The TCR gene usage was also heterogeneous. V beta 5.2, a peptide of which is currently being used in a clinical trial for treatment of MS patients, was expressed by only one of our TCL. However, within this complex pattern of MBP-specific T cell responses, a minority of MS patients were found to exhibit a more restricted response with respect to their TCL epitope specificity. In these patients 75-87% of the TCL responded to a single, patient-specific cluster of immunodominant T cell epitopes located within a small (20-amino acid) domain of MBP. These nested clusters of immunodominant epitopes were noted within the amino acids 80-105, 108-131, and 131-153. The T cell response to the immunodominant epitopes was not monoclonal, but heterogeneous, with respect to fine specificity, TCR usage, and even HLA restriction. In one patient (H.K.), this restricted epitope profile remained stable for > 2 yr. The TCR beta chain sequences of TCL specific for the immunodominant region of HK are consistent with an oligoclonal response against the epitopes of this region (80-105). Further, two pairs of identical sequences were established from TCL generated from this patient at different times (June 1990 and June 1991), suggesting that some TCL specific for the immunodominant region persisted in the peripheral repertoire. The possible role of persistent immunodominant epitope clusters in the pathogenesis of MS remains to be established.

Reactivity to myelin antigens in multiple sclerosis. Peripheral blood lymphocytes respond predominantly to myelin oligodendrocyte glycoprotein

Although T cell responses to the quantitatively major myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP), are likely to be of importance in the course of multiple sclerosis (MS), cell-mediated autoimmune responses to other myelin antigens, in particular quantitatively minor myelin antigens, such as myelin-associated glycoprotein (MAG) and the central nervous system-specific myelin oligodendrocyte glycoprotein (MOG), could also play a prevalent role in disease initiation or progression. Highly purified myelin antigens were used in this study to assess cell-mediated immune response to MOG in MS patients, in the context of the reactivity to other myelin antigens, MBP, PLP, and MAG. The greatest incidence of proliferative response by MS peripheral blood lymphocytes was to MOG, as 12 of 24 patients tested reacted and, of these, 8 reacted to MOG exclusively. In contrast, only 1 control individual of 16 tested reacted positively to MOG. The incidence of responses to MBP, PLP, and MAG did not differ greatly between MS patients and control individuals. A predominant T cell reactivity to MOG in MS suggests an important role for cell-mediated immune response to this antigen in the pathogenesis of MS.

Myelin basic protein purification in non denaturing conditions

The utilization of denaturing methods for protein purification causes the irreversible loss of quaternary and tertiary structure together with consistent changes in the secondary structure. These modifications reflect on protein antigenicity. MBP is a myelin protein which is bound to membrane-phospholipids. Its tertiary structure is specific for this kind of interaction which determines its native conformation. MBP was obtained in two forms: denatured and non denatured. The latter has been purified using the non-ionic detergent beta-octil-D-glucopyranoside which is able to preserve protein tertiary structure separating it from the bilayer phospholipids. Non denaturated MBP could be useful in antibody and/or lymphocyte activity detection studies in various human pathological processes.

Mechanical loading activates mitogen-activated protein kinase and S6 peptide kinase in cultured rat cardiac myocytes

The molecular mechanisms by which overloaded cardiac myocytes increase the cell size (hypertrophy) remain unknown. We have previously shown that mechanical loading increased the protein synthesis and the expression of proto-oncogene c-fos mRNA (Komuro, I., Kaida, T., Shibazaki, Y., Kurabayashi, M., Katoh, Y. Hoh, E., Takaku, F., and Yazaki, Y. (1990) J. Biol. Chem. 265, 3595-3598; Komuro, I., Katoh, Y., Kaida, T., Shibazaki, Y., Kurabayashi, M., Hoh, E., Takaku, F., and Yazaki, Y. (1991) J. Biol. Chem. 266, 1265-1268). It has been known that both mitogen-activated protein (MAP) kinase and S6 kinase can be activated by many kinds of growth factors. To clarify whether MAP kinase(s) and S6 kinase(s) are associated with the intracellular signaling of cardiac hypertrophy induced by mechanical loading, we cultured neonatal rat cardiac myocytes in deformable dishes and imposed an in vitro mechanical loading by stretching the adherent myocytes. In this study, we demonstrated that 1) myocyte stretching maximally activated a kinase activity toward myelin basic protein (MBP) at 10 min after stretching, and the kinase activity returned to the control level at 30 min after stretching; 2) kinase assays in MBP-containing gel, after sodium dodecyl sulfate-polyacrylamide gel electrophoresis, revealed that stretch-induced MBP kinase activity mainly migrated at 42 kDa in the immunoprecipitated fraction of anti-MAP kinase antibody, suggesting that the stretching mainly increased the 42-kDa MAP kinase activity in cardiac myocytes; 3) phosphorylation of MAP kinase was induced after stretching cardiac myocytes; 4) when protein kinase C was depleted by preincubating myocytes with 100 nM 12-O-tetradecanoyl-phorbol-13-acetate for 24 h or 2 nM staurosporine for 30 min, stretch-induced MBP kinase activity was decreased by approximately 60-70% as compared with the kinase activity in myocytes without protein kinase C depletion; 5) although the receptor tyrosine kinases were depleted by preincubating myocytes with 50 microM tyrphostin or 20 microM genistein for 30 min, there was no change in the stretch-induced MBP kinase activity; 6) stretch-induced MBP kinase activity was partially dependent on transsarcolemmal influx of Ca2+; 7) myocyte stretching also increased S6 peptide (RRLSSLRA) kinase activity in the anti-S6 kinase II antibody immunoprecipitates. From these results, we conclude that myocyte stretching increases the activities of MAP kinase and S6 peptide kinase, which may play an important role in the induction of the specific genes and the increase in the protein synthesis.

Studies on NG-methylarginine derivatives in myelin basic protein from developing and mutant mouse brain

The amounts of NG-methylarginine derivatives in myelin basic protein (MBP) purified from dysmyelinating mutant and different stages of normal myelinating mouse brains have been studied by using h.p.l.c. with a highly sensitive post-column o-phthaldialdehyde derivative-formation method. All three naturally occurring derivatives (NG-monomethylarginine (MeArg), NGN'G-dimethylarginine [Me2(sym)Arg] and NGNG-dimethylarginine [Me2(asym)Arg]) were found in MBP; however, their relative concentrations varied significantly with the age of the animal. The amounts of MeArg and Me2(sym)Arg in MBP increased as a function of the age of the brain, whereas that of Me2(asym)Arg decreased. MBP from early-myelinating mouse brain was shown to contain a high proportion of Me2(asym)Arg, which was hardly detectable in older brain MBP. This derivative, Me2(asym)Arg, was also absent from MBP embedded in the most compact multilamellar myelin, but was present in MBP in the least compact myelin (P3B). Comparing the extent of total methylation in vivo (sum of all three arginine derivatives), MBP extracted from less-compact myelin (P3A and P3B) showed a level approx. 40% higher than that from compact myelin. MBPs isolated from dysmyelinating mutant mouse brains, such as jimpy (jp/y) and quaking (qk/qk), contained a much higher level of Me2(asym)Arg relative to the other two methyl derivatives and also in comparison with those levels in the mother brain MBP. SDS/PAGE analysis of MBPs extracted from the mutant (both jp/y and qk/qk) as well as young normal (6-13 days old) mouse brains indicated the presence of a high-molecular-mass isoform of MBP (about 32 kDa), but this isoform was not found in adult brains. These results therefore indicate that structural integrity of myelin membrane in which MBP is embedded appears to play a pivotal role in determining the extent and the kind of Me2Arg formation in MBP at the post-translational level.

Identification of water-soluble proteases in myelin preparations

Sodium chloride extracts obtained from purified bovine brain myelin were found to contain proteolytic activity capable of degrading isolated myelin basic protein as assessed by SDS gel electrophoresis. Using gels copolymerized with gelatin as substrate, two bands at about 54 and 117-125 KDa, respectively, were detected. Activity corresponding to the 54 KDa band was inhibited by zinc. Data presented in this article suggest that proteolytic activity can be released from the myelin sheath in water-soluble form and recognize MBP as substrate.

The N terminus of human myelin basic protein consists of C2, C4, C6, and C8 alkyl carboxylic acids

Peptide 1-21, generated by cyanogen bromide cleavage of each of two highly purified components of human myelin basic protein, components 1 and 8, gave a series of peaks in the fast atom bombardment mass spectra with m/z 2299, 2327, 2355, 2383, and 2411, indicating additions of 42, 70, 98, 126, and 154 atomic mass units respectively with m/z 2327 and 2355 as the dominant species. The pentafluorobenzyl esters prepared from an acid hydrolysate analyzed by negative ion chemical ionization gas chromatography mass spectrometry confirmed that C6, C8, and C10 fatty acids were present. These data demonstrated (i) that the N terminus of a myelin basic protein is not simply acetylated but contains C2, C4, C6, C8, and C10 fatty acids with C4 and C6 as the dominant species, (ii) the two components studied (C-1 and C-8) showed different relative amounts of C2 and C8 in particular, and (iii) human myelin basic protein is the first protein to be reported with a complex N terminus consisting of several alkyl carboxylic acid species.

Isolation and characterization of two novel peptide amides originating from myelin basic protein in bovine brain

During a systematic search for peptides that possess the C-terminal amide structure, two novel peptide amides, one with a tyrosine amide and the other with an alanine amide were isolated from bovine brain by acid extraction and sequential steps of reversed phase HPLC. Microsequence, amino acid and mass spectral analyses revealed the structures: Ac-Ala-Ala-Gln-Lys-Arg-Pro-Ser-Gln-Arg-Ser-Lys-Tyr-amide and Ac-Ala-Ala-Gln-Lys-Arg-Pro-Ser-Gln-Arg-Ser-Lys-Tyr-Leu-Ala-Ser-Ala-amide . These 12 and 16 residues peptides had the primary structure identical to the N-terminal fragment of myelin basic protein (MBP). The peptides were therefore designated myelin peptide amide-12 (MPA-12) and -16 (MPA-16). Unlike other amidated peptides, MPA might be generated from MBP by hydroxyl radicals produced via a Fenton reaction in situ. However, this unique amidation seems to occur exclusively to MBP in a site specific manner in the brain.

Purification of primary antibodies of the myelin basic protein antibody cascade from multiple sclerosis patients. Immunoreactivity studies with homologous and heterologous antigens

Previous research has demonstrated a myelin basic protein (MBP) antibody cascade in cerebrospinal fluid (CSF) of multiple sclerosis (MS) patients. The purpose of this study was to determine whether primary antibodies to MBP (anti-MBP) reacted similarly with homologous (human) and heterologous (bovine and porcine) MBP. Myelin basic protein was prepared from central nervous system white matter of humans as well as bovine and porcine species. Immunoglobulin G (IgG) was purified by protein A-Sepharose affinity chromatography from concentrated CSF of MS patients with active or inactive disease or from non-MS controls. Antibodies to MBP were isolated from purified CSF IgG of MS patients with acute relapses by two-step antigen specific (MBP-Sepharose) affinity chromatography. Anti-MBP in the context of whole CSF, in purified CSF-IgG or as purified antibody, reacted identically with homologous and heterologous MBP. Kinetic studies of anti-MBP titers demonstrated that when anti-MBP was reacted in vitro with increasing amounts of homologous or heterologous MBP, the antibody was equally neutralized by either antigen. Neutralization of anti-MBP by homologous and heterologous MBP or their synthetic peptides may also be possible in vivo as a potential therapeutic tool.

Autoantigen-induced self lysis of human myelin basic protein-specific T lymphocytes

Cytotoxic T cells reactive with myelin basic protein (MBP) may be isolated from most human subjects. Since activated T cells express major histocompatibility complex (MHC) class II antigens, we assessed whether MBP-specific, CD4+ T cells could present MBP or synthetic MBP peptides to themselves and whether this provoked self lysis. We examined two MBP-specific cell lines and eight T cell clones recognizing four different MBP epitopes. All T cell populations presented MBP as well as synthetic peptides to themselves eliciting self lysis of the T cell clones. CD4+ T cell populations recognizing another central nervous system (CNS) protein, proteolipid protein (PLP), or the recall antigen, Candida, did not exhibit this antigen-induced, autocytolytic activity. However, activated, PLP-reactive T cells were susceptible to lysis by cytotoxic MBP-specific T cells in the presence of MBP. These results suggest that antigen-induced self lysis of activated human T cells might limit an autoimmune response within a target organ independent of other immunoregulatory mechanisms.

Insulin-sensitive myelin basic protein phosphorylation on tyrosine residues

Rat brain plasma membranes were solubilized in detergent and a glycoprotein-enriched fraction was obtained by lectin affinity chromatography. This glycoprotein fraction contained insulin receptors, as well as protein kinases capable of phosphorylating some exogenously added substrates such as MAP2 (microtubule associated protein 2) and MBP (myelin basic protein), but not ribosomal protein S6. Phosphoamino acid analysis of MAP2 and MBP showed that phosphotyrosine residues, as well as phosphoserine/phosphotheronine residues, were present in both proteins under basal conditions. Whereas the addition of insulin to the rat brain membrane glycoprotein fraction in vitro had no effect on MAP2 phosphorylation, MBP phosphorylation was stimulated 2.7-fold in response to insulin. This phenomenon was dose-dependent, with half-maximal stimulation of MBP phosphorylation observed with 2 nM insulin. Phosphoamino acid analysis of MBP indicated that insulin stimulated the phosphorylation of tyrosine residues nearly three-fold, whereas the phosphorylation of serine or threonine residues was not increased. These results identify MBP as a substrate for the rat brain insulin receptor tyrosine-specific protein kinase in vitro.

T-cell receptor peptide immunization leads to enhanced and chronic experimental allergic encephalomyelitis

It has previously been reported that synthetic peptides corresponding to sequences derived from T-cell receptor variable regions identified as dominant in the T-cell-mediated autoimmune disease experimental allergic encephalomyelitis in both the mouse and the rat can down-regulate disease in Lewis rats. In contrast to these results, we have found that immunization of Lewis rats with such peptides in complete Freund's adjuvant prior to induction of experimental allergic encephalomyelitis with myelin basic protein leads to responses ranging from profound disease enhancement to lack of disease. In some cases, enhanced disease was followed by a prolonged neurologic deficit that resembles multiple sclerosis more closely than does acute experimental allergic encephalomyelitis. These findings, on the one hand, support previous results showing T-cell receptor peptide-induced modulation of the disease experimental allergic encephalomyelitis and, on the other, indicate that such immunization is not a reliable method for inducing suppression of encephalitogenic effector cells.