Properties, structure and possible neuroreceptor role of the encephalitogenic protein of human brain

Biological methylation of myelin basic protein: enzymology and biological significance

Myelin is a membrane characteristic of the nervous tissue and functions as an insulator to increase the velocity of the stimuli being transmitted between a nerve cell body and its target. Myelin isolated from human and bovine nervous tissue is composed of approximately 80% lipid and 20% protein, and 30% of the protein fraction constitutes myelin basic protein (MBP). MBP has an unusual amino acid at Res-107 as a mixture of NG-monomethylarginine and NG, N'G-dimethylarginine. The formation of these methylarginine derivatives is catalysed by one of the subtypes of protein methylase I, which specifically methylates Res-107 of this protein. Evidence is presented to demonstrate an involvement of this biological methylation in the integrity and maintenance of myelin.

Autoantibodies to HMG-17 nucleosomal protein in autoimmune rheumatic diseases. Correlation with systemic lupus erythematosus clinical activity and with antibodies to double-stranded DNA

OBJECTIVE

Previous studies have shown that serum from patients with systemic lupus erythematosus (SLE) contains antibodies directed against HMG-17, a nucleosomal nonhistone high mobility group (HMG) protein found in chromatin. The aim of the present study was to investigate any associations between the presence of antibodies to HMG-17 and clinical and serologic features of SLE.

METHODS

Using porcine thymus as a source, HMG-17 was purified by Sephacryl S-200 chromatography followed by high performance liquid chromatography. An enzyme-linked immunosorbent assay utilizing the purified HMG-17 as antigen was developed and was used to evaluate sera from patients with autoimmune rheumatic diseases, for the presence of autoantibodies.

RESULTS

Anti-HMG-17 antibodies were found in the serum of 34.8% of the patients with SLE, compared with 11.5% of patients with primary Sjögren's syndrome, 4.4% of patients with rheumatoid arthritis, and 4.1% of normal blood donors. Analysis of the clinical features of SLE using 2 different lupus activity indices revealed that anti-HMG-17 antibodies were more frequently found in patients with active disease. A positive correlation was also observed between anti-HMG-17 and anti-dsDNA levels, and levels of both of these autoantibodies demonstrated a negative correlation with C4. Analysis of sequentially obtained serum samples from 4 SLE patients revealed that, in 2 patients, anti-HMG-17 levels fluctuated in parallel with both disease activity and anti-dsDNA levels, and in the remaining 2, anti-HMG-17 levels fluctuated in parallel with disease activity.

CONCLUSION

Antibodies to HMG-17 are found in patients with many different autoimmune rheumatic diseases, although they are more frequently observed in those with SLE. Their presence appears to be associated with lupus disease activity as well as with anti-dsDNA and C4 levels.

Folding and function of the myelin proteins from primary sequence data

To explain how the myelin proteins are involved in the organization and function of the myelin sheath requires knowing their molecular structures. Except for P2 basic protein of PNS myelin, however, their structures are not yet known. As an aid to predicting their molecular folding and possible functions, we have developed a FORTRAN program to analyze the primary sequence data for proteins, and have applied this to the myelin proteins in particular. In this program, propensities for the secondary structure conformations as well as physical-chemical parameters are assigned to the amino acids and the pattern of these parameters is examined by calculating their average values, autocorrelation functions and Fourier transforms. To compare two proteins, their sequences are aligned using a unitary scoring matrix, and homologies are searched by plotting a two-dimensional map of the correlation coefficients. Comparison of the corresponding myelin basic proteins (MBP) and P0 glycoproteins (P0) for rodent and shark showed that the conserved residues included most of the amino acids which were predicted to form the alpha or beta conformations, while the altered residues were mainly in the hydrophilic and turn or coil regions. In both rodent and shark the putative extracellular domain of P0 glycoprotein displayed consecutive peaks of beta propensity similar to that for the immunoglobulins, while the cytoplasmic domain showed alpha-beta-alpha folding. To trace the immunoglobulin fold along the P0 sequence, we compared the beta propensity curve of P0 with that of the immunoglobulin M603, whose three-dimensional structure has been determined. We propose that the flat beta-sheets of P0 are orientated parallel to the membrane surface to facilitate their homotypic interaction in the extracellular space. An extra beta-fold in the extracellular domain of shark P0 compared with rodent P0 was found, and this may result in a greater attraction between the apposed extracellular surfaces and may account for a smaller extracellular space as measured by x-ray diffraction. A computer search of the myelin protein sequences for functional motifs revealed sites for N-glycosylation, phosphorylation, nucleotide binding, and certain enzyme activities. We note especially that there are potential nucleotide binding sites in proteolipid protein (PLP), MBP and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP). This is consistent with the experimental observations that PLP acts like an ionophore or proton channel when reconstituted into planar lipid bilayers, MBP binds GTP, and CNP catalyzes in vitro the hydrolysis of 2',3'-nucleotides into corresponding 2'-nucleotides.

Peptide displacement of [3H]5-hydroxytryptamine binding to bovine cortical membranes

Chemical studies have demonstrated that peptides such as the encephalitogenic (EAE) peptide of myelin basic protein (MBP) and luteinizing hormone-releasing hormone (LHRH) can bind serotonin (5-hydroxytryptamine, 5-HT) in vitro. The present research was undertaken to determine whether such binding interferes with 5-HT binding to its 5-HT1 receptors on bovine cerebral cortical membranes. EAE peptide and LHRH displaced [3H]5-HT with IC50s of 4.0 x 10(-4) and 1.8 x 10(-3) M respectively. MBP itself also showed apparent displacing ability with an IC50 of 6.0 x 10(-5) M, though it also caused aggregation of cortical membranes that might have interfered with normal receptor binding. These results support previous suggestions that the tryptophan peptide region of MBP may act as a 5-HT receptor in the neural system. We also tested the effects of muramyl dipeptide (N-acetyl-muramyl-L-Ala-D-isoGln, MD), a bacterial cell-wall breakdown product that acts as a slow-wave sleep promoter, binds to LHRH and EAE peptide, and competes for 5-HT binding sites on macrophages. It showed no significant displacement of 5-HT binding to cortical membranes (IC50 greater than 10(-1) M), but its D-Ala analogue did (IC50 = 1.7 x 10(-3) M). Thus, it seems likely that the 5-HT-related effects of naturally occurring muramyl peptides are physiologically limited by receptor types.

Serotonin binding sites. II. Muramyl dipeptide binds to serotonin binding sites on myelin basic protein, LHRH, and MSH-ACTH 4-10

Previously, we reported the existence of structurally similar serotonin binding sites on myelin basic protein, LHRH, and MSH-ACTH 4-10. We now report that the adjuvant peptide, muramyl dipeptide (N-acetyl-muramyl-L-Ala-D-isoGln) also binds to these sites. This observation may help to explain previous observations of serotonin-like activity by muramyl peptides, including the promotion of slow-wave sleep and fever induction. The observation may also provide an important link between the immune system and the nervous system that may explain the role of muramyl dipeptide adjuvants in causing autoimmune diseases to serotonin-regulated proteins and their receptors, as well as the alterations in serotonin levels that are often observed in autoimmune diseases. The observation provides concrete evidence for a dual-antigen hypothesis for the induction of autoimmune diseases by an adjuvant-peptide complex. Application of such a mechanism for induction of autoimmunity may be of importance in understanding a number of postinfectious and postvaccinal neuropathies, and suggests a possible etiology for autism, in which many patients have high blood serotonin levels, autoimmune reactions to myelin basic protein, and antibodies to serotonin binding sites. Finally, the observation suggests that glycopeptides may act as neurotransmitters.

Demyelination and early remyelination in experimental allergic encephalomyelitis passively transferred with myelin basic protein-sensitized lymphocytes in the Lewis rat

Histological studies were performed on Lewis rats with experimental allergic encephalomyelitis (EAE) passively transferred by myelin basic protein (MBP)-sensitized syngeneic spleen cells in order to determine the relationship between demyelination and neurological signs. Neither inflammation nor demyelination was present on the day prior to the onset of neurological signs but both were present in the spinal roots and spinal cord on the day of onset of tail weakness (4 days after passive transfer). Demyelination and the neurological signs both increased over the next 48 h. There was evidence that the caudal roots were more severely affected than the rostral roots. The peripheral nerves were spared. Demyelination in the spinal cord was concentrated in the dorsal root entry and ventral root exit zones. The initial stages of repair of demyelinated spinal root fibres by Schwann cells were observed on the earliest day that clinical recovery commenced (day 7). At this time some demyelinated fibres were closely associated with debris-free Schwann cells, and occasional fibres were completely invested by 1-2 layers of Schwann cell cytoplasm. Remyelination (compact myelin lamellae formation) by Schwann cells was first observed in the spinal roots on day 9. By the time of complete clinical recovery (day 11) the majority of affected spinal root cores had thin new myelin sheaths. Repair of central nervous system myelin by oligodendrocytes was slower than peripheral nervous system myelin repair. Investment of demyelinated spinal cord axons by oligodendrocytes was observed on day 9, and remyelination by these cells was seen on day 10. We conclude that the neurological signs of passively induced MBP-EAE can be accounted for by demyelination of the lumbar, sacral and coccygeal spinal roots and spinal cord root entry and exit zones, and that the subsequent clinical recovery can be explained by investment and remyelination of demyelinated peripheral and central nervous system fibres by Schwann cells and oligodendrocytes respectively.

The pathophysiology of acute experimental allergic encephalomyelitis induced by whole spinal cord in the Lewis rat

Histological and electrophysiological studies were performed on Lewis rats with acute experimental allergic encephalomyelitis (EAE) induced by inoculation with guinea-pig spinal cord and Freund's adjuvants, in order to determine the cause of the neurological signs. These studies demonstrated demyelination-induced nerve conduction block in the large and also the smaller diameter fibres at the ventral root exit zone (VREZ) of the lumbar spinal cord. The demyelination at the VREZ affected both centrally and peripherally myelinated internodes, but predominantly the former. Studies on the H reflex recorded from a hindfoot muscle indicated normal peripheral nerve motor conduction but interruption of the monosynaptic reflex arc, as would be anticipated from this efferent conduction block and previously reported afferent conduction abnormalities. It is concluded that conduction block in alpha, beta and gamma motor fibres at the VREZ is an important cause of hindlimb weakness in whole spinal cord-induced acute EAE.

Cellular and molecular aspects of myelin protein gene expression

The cellular and molecular aspects of myelin protein metabolism have recently been among the most intensively studied in neurobiology. Myelination is a developmentally regulated process involving the coordination of expression of genes encoding both myelin proteins and the enzymes involved in myelin lipid metabolism. In the central nervous system, the oligodendrocyte plasma membrane elaborates prodigious amounts of myelin over a relatively short developmental period. During development, myelin undergoes characteristic biochemical changes, presumably correlated with the morphological changes during its maturation from loosely-whorled bilayers to the thick multilamellar structure typical of the adult membrane. Genes encoding four myelin proteins have been isolated, and each of these specifies families of polypeptide isoforms synthesized from mRNAs derived through alternative splicing of the primary gene transcripts. In most cases, the production of the alternatively spliced transcripts is developmentally regulated, leading to the observed protein compositional changes in myelin. The chromosomal localizations of several of the myelin protein genes have been mapped in mice and humans, and abnormalities in two separate genes appear to be the genetic defects in the murine dysmyelinating mutants, shiverer and jimpy. Insertion of a normal myelin basic protein gene into the shiverer genome appears to correct many of the clinical and cell biological abnormalities associated with the defect. Most of the dysmyelinating mutants, including those in which the genetic defect is established, appear to exhibit pleiotropy with respect to the expression of other myelin genes. Post-translational events also appear to be important in myelin assembly and metabolism. The major myelin proteins are synthesized at different subcellular locations and follow different routes of assembly into the membrane. Prevention of certain post-translational modifications of some myelin proteins can result in the disruption of myelin structure, reminiscent of naturally occurring myelin disorders. Studies on the expression of myelin genes in tissue culture have shown the importance of epigenetic factors (e.g., hormones, growth factors, and cell-cell interactions) in modulating myelin protein gene expression. Thus, myelinogenesis has proven to be very useful system in which to examine cellular and molecular mechanisms regulating the activity of a nervous system-specific process.

Use of protein-bearing nitrocellulose as immunogen for in vitro production of monoclonal antibodies: application to myelin basic protein electrophoretically separated from a complex brain protein mixture

A procedure for producing monoclonal antibody to myelin basic protein (MBP) using in vitro immunization with MBP transferred to nitrocellulose is described. Following the separation of brain proteins by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and electrophoretic transfer of the electrophoretogram onto nitrocellulose, the MBP band located by immunodetection was excised from the nitrocellulose, ground, and used as immunogen for in vitro stimulation of unprimed mouse spleen cells. While in vitro immunization with soluble MBP was able to generate many hybrids, all the wells in the fusions carried out with the immobilized MBP contained hybrids, 33 to 42% of which were positive to MBP. Among these, six were further characterized; all were IgM and all bound to epitopes common to the 18.5K and 21.5K MBP forms of several species. In view of its simplicity, this technique should have a wide application for the rapid production of monoclonal antibodies to selected proteins or their fragments present in small quantity or difficult to purify on a large scale.

Demyelination and neurological signs in experimental allergic encephalomyelitis

Because of the reported absence of demyelination in some animals with neurological signs of experimental allergic encephalomyelitis (EAE), it has been suggested that these signs are not due to demyelination. The present study demonstrates that there is ample demyelination in the central nervous system (CNS) and peripheral nervous system (PNS) to account for the neurological signs in rats with myelin basic protein (MBP)-induced acute EAE as well as in rats and rabbits with whole-spinal-cord-induced acute EAE. The main reasons for failure to detect demyelination in animals with neurological signs of EAE appear to be inadequate histological techniques and incomplete examination of the nervous system, particularly the PNS and the lumbar, sacral and coccygeal segments of the spinal cord.

Determination of methylated basic, 5-hydroxylysine, elastin crosslinks, other amino acids, and the amino sugars in proteins and tissues

Analytical single-column chromatographic methods have been developed for determining all methylated basic amino acids, isodesmosine, desmosine, the amino sugars glucosamine and galactosamine, the diastereoisomers of 5-hydroxylysine, and related compounds at picomole levels in protein and tissue hydrolysates. Complete resolution of all these unique basic amino acids as discrete peaks was achieved in 5.4 on a 50 X 0.28-cm microcolumn of Dionex type DC-4A spherical resin (9.0 +/- 0.5 micron) using updated instrumentation commonly available for amino acid analysis. The column was operated at 5.65 ml/h with two 0.35 M sodium citrate buffers (pH 5.700 and 4.501), at two temperatures (31.5 and 73 degrees C). Excellent resolution of all omega-N-methylarginines and related compounds was also achieved in 3 h using a 17.5 X 0.28-cm microcolumn of Dionex DC-5A resin (sized to 6.0 +/- 0.5 microns), two citrate buffers (0.21 M Na+, pH 5.125; 0.35 M Na+, pH 5.700), a buffer flow rate of 5.75 ml/h, and a temperature of 52 degrees C. Complete separation of all other amino acids found in protein or tissue hydrolysates including S-carboxymethyl cysteine, 4-hydroxyproline, methionine S,S-dioxide, and the amino sugars was also carried out in 95 min using a 23.5 X 0.28-cm microcolumn of Dionex DC-5A resin. The use of purified microcolumn buffers gave smooth baselines without interference from artifacts or minor hydrolysate components. The major advantages of these methods are: first, their high resolving power; second, their high sensitivity which is comparable and in some aspects superior to the newer instruments; and third, their high reproducibility (100 +/- 2.5%) and low operating costs. These methods should be especially valuable for determining myosin, actin, and elastin in tissue hydrolysates from the amounts of N tau-methylhistidine, desmosine, or isodesmosine present, respectively, and for studying protein methylation, hydroxylation, cross-linking formation, and the turnover rates of contractile and connective tissue proteins in biological systems.

Myelin basic protein inhibits histone-specific protein methylase I

Bovine brain myelin basic protein, free of associated proteolytic activity, was found to be a specific inhibitor of histone-specific protein methylase I (S-adenosyl-L-methionine:protein-L-arginine N-methyltransferase, EC 2.1.1.23) purified from bovine brain. 50% of the methyl group incorporation into the histone substrate catalyzed by the methylase I was inhibited by myelin basic protein at a concentration of 0.326 mM. However, neither of the peptide fragments (residues 1-116 and residues 117-170) generated by the chemical cleavage of myelin basic protein at the tryptophan residue retained the inhibitory activity for histone-specific protein methylase I. Proteins such as gamma-globulin, bovine serum albumin, bovine pancreatic ribonuclease and polyarginine did not exhibit significant inhibitory activity toward the enzyme. The Ki value for myelin basic protein was estimated to be 3.42 X 10(-5) M for histone-specific protein methylase I and the nature of the inhibition was uncompetitive toward histone substrate.

Changes of neurotransmitter systems in chronic relapsing experimental allergic encephalomyelitis in rat brain and spinal cord

Catecholamine and indoleamine neurotransmitters, together with some of their precursors and metabolites, were determined using HPLC in three brain and two spinal cord regions of Lewis rats with chronic relapsing allergic encephalomyelitis and of control rats injected with complete Freund's adjuvant. Three attacks and two recovery phases were investigated. Changes are found mainly in the spinal cord. In the lumbosacral region both 5-hydroxytryptamine and noradrenaline are reduced during the entire course of the disease, whereas in the craniothoracal region 5-hydroxytryptamine is unchanged and only noradrenaline is reduced during the attacks, returning to normal during the first recovery. The precursors tyrosine and tryptophan are greatly elevated during the first two attacks in both regions. The 5-hydroxytryptamine turnover marker 5-hydroxyindoleacetic acid is increased in the first attack in both regions, then it decreases in the later stages, indicating destruction of nerve fibers. On the fourth and seventh days after inoculation values are generally not significantly different from controls in all regions. The possible correlation of neurochemical results with neurological signs is discussed.

Conduction block due to demyelination at the ventral root exit zone in experimental allergic encephalomyelitis

Histological and electrophysiological studies were performed in Lewis rats with experimental allergic encephalomyelitis (EAE) to determine the cause of the neurological signs. The ventral root exit zone of the spinal cord was shown to be a major site of demyelination and conduction block. It is concluded that demyelination-induced conduction block in this region is an important cause of hindlimb weakness and paralysis in Lewis rats with EAE.

Treatment of cancer by alteration of a cancer specific surface membrane epitope

Since cancer is essentially a cell surface problem with loss of contact inhibition, effort might be directed to restoring such inhibition by interfering with activity of new determinants on the cancer cell surface associated with the contact inhibition loss.

Monoclonal and polyclonal antibodies to myelin basic protein determinants

A detailed immunochemical examination of monoclonal and polyclonal antibody responses to myelin basic protein (MBP) and its peptides has revealed the existence of as many as 27 antigenic determinants, many of them conformational. Topological mapping of the potential antigenic determinants onto a model of MBP secondary structure places these determinants within 11 separate regions of the molecule, including those portions that have been found to be encephalitogenic. MBP and its peptides, therefore, fall under the umbrella of the Multideterminant-Regulatory Model of Benjamin et al. (1984). However, in the case of MBP, multideterminant immunogenicity appears to represent mainly an escape from tight regulation through the avenue of conformational change.

Myelin basic protein and demyelinating diseases

Myelin basic protein (MBP) is a major protein component of myelin sheath. Primarily because of its ability to induce experimental allergic encephalomyelitis (EAE) in animals, this protein has been considered to play an important role in the pathogenesis of multiple sclerosis (MS), which is one of the most common demyelinating diseases. Its precise measurement in the cerebrospinal fluid (CSF) has been uncommonly difficult, mainly due to immunoheterogeneity of MBP or MBP-like material. More recently, highly sensitive radioimmunoassay techniques utilizing well-characterized antisera have been developed that facilitated its use in the management of MS. The clinical course of MS is highly variable, and the disease is characterized by periods of remission and relapses. Many studies have demonstrated the release of MBP during relapses and elevated levels of MBP in the CSF can be detected if lumbar puncture is performed within 7 days of the onset of neurologic symptoms suggestive of MS. However, the presence of MBP is not an absolute indicator of MS, as elevated MBP levels are also frequently observed in other demyelinating diseases.

Multiple sclerosis in research workers studying swayback in lambs: an updated report

Four out of seven research workers into swayback disease, a neurological disease of lambs, developed symptoms and signs of multiple sclerosis, and were reported in 1947. A further worker later joined the group. All of the original seven have died and two at necropsy had multiple areas of demyelination in the brain and spinal cord. The chance of four or more out of a random group of eight men developing multiple sclerosis is about one in a thousand million. Multiple sclerosis has not occurred in other workers on swayback disease elsewhere.

A serum factor cross-reactive with antibodies to a determinant of rabbit encephalitogenic sequence 65-74 of myelin basic protein

A serum factor, cross-reactive with antibodies to a defined determinant of myelin basic protein (residues 66-71), has been found in the sera of nine mammalian species where it may function as a specific neuroautotolerogen. In equilibrium competitive inhibition radioimmunoassays the factor appears to be completely competitive with synthetic peptide S24 (TTHYGSLPQKG) at high affinity and is therefore termed MBP-SF-24 (myelin basic protein serum factor of the S24 type). The bulk of the activity can be recovered by ammonium sulfate fractionation at 61.1% saturated ammonium sulfate (SAS), pH 7, (fraction E) after removal by precipitation at pH 7 of the 37.5, 42.6, 47.5, and 51.4% SAS fractions (fractions A-D), including the immunoglobulins, and before removal by precipitation at pH 5 of the albumin fraction (fraction F). The factor, by its retention on XM300 during ultrafiltration of fraction E, can be purified 20-fold from serum proteins without much loss through a combination of SAS fractionation and ultrafiltration. The yield of MBP-SF-S24 in fraction E may range from a low 26 pmol S24 equivalents from 10 ml in sheep serum to a high 1.7 nmoles from 10 ml rat serum. The serum factor is reactive at high affinity with each of two populations of S24-reactive antibodies in one rabbit reagent antiserum and with one of two populations of S24-reactive antibodies in another. It appears to express a determinant involving residues THYGSL (66-71) of myelin basic protein with the same conformation as found in intact S24.

GABA-modulin: a synaptosomal basic protein that differs from small myelin basic protein of rat brain

GABA-modulin, a basic protein that allosterically inhibits the high-affinity binding of GABA to its recognition sites, has been extracted and purified from the synaptosomal fraction of rat brain where it represents approximately 0.5% of the total synaptosomal proteins. GABA-modulin has characteristics in common to the class of highly basic proteins isolated from myelin, in particular to the rat small myelin basic protein (SMBP). However, GABA-modulin is located selectively in synaptosomes, whereas the SMBP is located in myelin. Moreover, synaptosomal GABA-modulin is different from SMBP in amino acid composition (it contains more Glx and Lys and fewer Arg residues) and in apparent molecular weight (17,000 and 15,000 for GABA-modulin and SMBP, respectively). Synaptosomal GABA-modulin fails to bind [3H]muscimol per se but noncompetitively inhibits (IC30 approximately 0.5 microM) the binding of [3H]muscimol to purified synaptic membranes. Cyanogen bromide treatment generated a 13,000 MW major fragment from both SMBP and GABA-modulin. These two fragments were compared and showed differences in amino acid composition and sequence. Moreover, the peptide maps generated from GABA-modulin and SMBP by trypsin and staphylococcal V8 protease digestion are different. The high concentration of GABA-modulin in synaptosomal membranes, its high potency in the inhibition of GABA binding, and its neuronal specificity suggest that GABA-modulin plays an important role in neuronal membrane function linked to the modulation of GABA and perhaps other neurotransmitter receptors.

A heme binding site on myelin basic protein: characterization, location, and significance

Myelin basic protein (MBP), an extrinsic membrane protein from the myelin sheath, binds dicyanohemin. The binding generates absorption bands in the Soret region and quenches the fluorescence emitted by the sole tryptophan residue. The absorption titration curves in the Soret demonstrate that the binding is stoichiometric, one heme per protein, with a large value of the extinction coefficient (8 X 10(4) M-1 cm-1 at 420 nm). Fluorescence quenching titration curves indicate an identical stoichiometry and a low quenching efficiency of 20%. From the heme titration curve the association constant between dicyanohemin and MBP is estimated to be greater than or equal to 10 nM-1 in 50 mM 4-morpholinepropanesulfonic acid buffer, pH 7.0, at 20 degrees C. Digestion of MBP by Staphylococcus aureus V8 protease yields a peptide (38-118) whose heme binding properties are identical to those of MBP. In contrast, peptides obtained by digestion of MBP with cathepsin D do not exhibit any specific binding of dicyanohemin. The cleavage of the Phe-Phe (42-43) bond appears to be critical in this respect. A comparison of the sequence immediately preceding, including these residues with a probable heme binding site of a mitochondrial cytochrome b, reveals a high degree of homology. The possible significance of heme binding is discussed.

Serotonin binding sites. I. Structures of sites on myelin basic protein, LHRH, MSH, ACTH, interferon, serum albumin, ovalbumin and red pigment concentrating hormone

We report the results of nuclear magnetic resonance spectroscopy studies of combinations of serotonin (5-hydroxytryptamine) with the tryptophan peptide sequence and similar peptides from myelin basic protein. The binding site appears to consist of the sequence Arg Phe Ser Trp. Similar serotonin binding sites were found to exist on LHRH (Tyr Ser Trp) and MSH-ACTH tetrapeptide (Phe Arg Trp). These binding sites are specific to serotonin as is demonstrated by lack of binding by dopamine, histamine, acetylcholine and a dozen other pharmacologically active amines and indoles. Drugs known to affect serotonin levels, e.g., fenfluramine and L-DOPA, bind weakly to these sites. Structural and functional similarities between the tryptophan peptide, LHRH, and MSH-ACTH with an ACTH-like peptide of human leukocyte interferon, with human and bovine serum albumin, hen ovalbumin, and with red pigment concentrating hormone suggest that the latter peptides may also contain similar serotonin binding sites. The elucidation of serotonin binding sites on these peptides and proteins has implications for understanding various aspects of cancer, autoimmunity, neurological disease, and peptide hormone control.

Glycosyl transferases of baby hamster kidney cells and ricin-resistant mutants. O-glycan biosynthesis

Extracts of baby hamster kidney (BHK) cells catalyzed the incorporation of N-acetylgalactosamine from UDP-N-acetyl[14C]galactosamine into myelin basic protein and an acylated tetrapeptide, N-acetylthreonyl-triproline, based on the threonine residue 98, glycosylated in myelin basic protein. The incorporated N-acetylgalactosamine residues were shown to be in alpha linkage to the peptide moieties. Several ricin-resistant BHK cell lines contained enhanced (approximately twofold) levels of the transferase activity. Apomucins obtained from bovine submaxillary gland mucin by chemical or enzymic degradation were relatively poor acceptors. Using asialomucin as acceptor, galactosyl, transferase activities and a weak sialyl transferase activity were detected in BHK cell extracts. Galactose transfer occurred at two sites: to peptide-linked N-acetylgalactosamine residues to form the linkage, galactosyl-(beta 1 leads to 3)-N-acetylgalactosamine and to terminally linked N-acetylglucosamine residues that exist as a minor constituent in bovine submaxillary mucin O-glycans, to form a galactosyl N-acetylglucosamine linkage. This reaction was not inhibited by ovalbumin, an efficient acceptor of the beta 1 leads to 4 galactosyl transferase involved in N-glycan assembly. Incorporation of galactose and N-acetylgalactosamine into endogenous proteins of BHK cell extracts was also detected. Sialic acid, fucose and N-acetylglucosamine residues were not incorporated. The incorporated N-acetylgalactosamine residues were shown to be in alpha linkage to polypeptide, and galactose incorporation represented synthesis of the galactosyl-(beta 1 leads to 3)-N-acetylgalactosamine sequence linked to polypeptide. The major endogenous protein labelled by either sugar had a molecular weight of approximately 80 000. A BHK-cell-associated glycoprotein, analogous to the urinary Tamm-Horsfall glycoprotein of molecular weight similar to the major endogenous acceptor of glycosylation, was not glycosylated in the experiments in vitro.

Fenfluramine binds 5-hydroxytryptophan

Fenfluramine, an anorexigenic drug, lowers serotonin (5-hydroxytryptamine) and 5-hydroxyindoleacetic acid levels in brain, spinal fluid, and blood, and has been used as a treatment for autism. Fenfluramine's mode of action is unknown. We present evidence from chromatography and nuclear magnetic resonance spectroscopy that fenfluramine selectively binds the serotonin and 5-hydroxyindoleacetic acid precursor, 5-hydroxytryptophan. The mode of binding may have general applications for the understanding of drug activity, receptor binding, and for the design of specific antagonists to aromatic compounds.

The structure of a serotonin and LSD binding site of myelin basic protein

Experiments have established the presence of a serotonin binding site in the tryptophan region of myelin basic protein. LSD competes for this binding site in vivo and in vitro. Although previous models have been suggested for the site, these models failed to explain the results of serotonin modification studies or the mode of LSD binding to the site. A new model of the site is proposed to rectify these problems. Means of testing the model are suggested. Implications for understanding neuroreceptor physiology, specificity, and disease are discussed. The name "molecular sandwiching" is suggested to describe the binding process.

Experimental autoimmune encephalomyelitis. An anatomically-based explanation of clinical progression in rodents

Lactate accumulation was measured soon after decapitation in three adjacent lower spinal cord regions of rats with EAE. Results indicate that during EAE, and in correlation with the onset of clinical signs of both initial attack and short-term relapse, a differential focal increase in lactate accumulation occurs in rat spinal cord compared to Freund's Complete Adjuvant controls, with greater increase occurring in more caudal segments. A [14C]antipyrine method of estimating relative spinal cord blood flow failed to find evidence that the lactate accumulations were due to focal ischemia. Subsequent measurement of isotopic water and total protein increases in the same cord regions indicated that a slight but significant increase in vasogenic edema occurs in correlation with the increase in lactate accumulation and the onset of EAE clinical signs. The data are interpreted as lending support to a speculative theory of paralysis induced by edema during EAE, in which nerve root endoneurium is postulated as the functionally vulnerable site. More specifically, it is hypothesized that the ascending progression of clinical signs of EAE in rodents can be explained on an anatomical basis by progressive disturbance of the nodes of Ranvier in nerve root myelinated fibers.

Cancer and depression: cancer presenting with depressive illness: an autoimmune disease?

It is proposed that some cases of depressive illness in cancer patients may be caused by immunological interference with the activity of serotinin, one of the neurotransmitters thought to be implicated in depression. This interference could be mediated in two ways. Antibody induced against a protein released from cancer cells could, on the basis of cross-reactivity with CNS tissue, bind to receptors for serotonin and block them. Such primary antibodies could stimulate the production of anti-idiotypic antibodies, which would act as an alternative receptor for serotonin and reduce its synaptic availability.

The effects of bovine myelin basic protein on the phase transition properties of sphingomyelin

The basic protein of myelin can spontaneously associate with the synthetic phospholipid N-palmitoyl-sphingosinephosphatidylcholine. The protein alters the phase transition properties of the lipid from a single transition at 41.5 degrees C to two overlapping transitions, one being slightly above and the other slightly below the transition temperature of the pure lipid. The effect was not seen upon the addition of poly(L-lysine) to this lipid nor does the myelin basic protein alter the phase transition properties of dimyristoylphosphatidylcholine. The results thus demonstrate that the myelin basic protein can interact with a major zwitterionic lipid component of myelin in addition to acidic phospholipids.

Species restriction of a monoclonal antibody reacting with residues 130 to 137 in encephalitogenic myelin basic protein

A monoclonal antibody (immunoglobulin G1) has been produced that reacts against myelin basic protein present in or extracted from the brains of many mammals-with certain important exceptions. Because of known species differences in amino acid sequences of basic protein and of certain peptide fragments, the binding site for this particular antibody appeared likely to include residues 130 to 137. Confirmation of this hypothesis was obtained by amino acid composition of the major immunoreactive peptides produced by thermolysin digestion of human basic protein and isolated by high-performance liquid chromatography.

Hind-limb motor ability in Lewis rats during the onset and recovery phases of experimental autoimmune encephalomyelitis

Hind-limb motor function in adult female Lewis rats with experimental autoimmune encephalomyelitis (EAE) was investigated using an objective behavioral measurement of motor ability. Rats were pretrained to avoid falling from the external surface of a power-driven running wheel. The performance of EAE-group rats on the wheel was then compared with that of saline and adjuvant controls immediately prior to the onset of clinical signs of EAE, and within 3 days of apparent recovery from EAE. Results indicate no apparent hind-limb motor deficit in the absence of overt clinical signs of EAE, despite histological evidence of severe inflammatory lesions persisting in the central nervous system (CNS) at the time of the post-recovery test. The remarkably transient nature of motor impairment is discussed within the context of a continuing search for the underlying cause(s) of clinical signs of EAE.

Equilibrium and nonequilibrium competitive inhibitions of antipeptide antibody binding by parent myelin basic protein and 18 related peptide sequences

Equilibrium and nonequilibrium competitive inhibition analyses of a number of antisera to peptide S81 and S82 sequences were carried out through the use of inhibition radioimmunoassays with [125I]S81, [125I]S82, and [125I]S79 and a panel containing 18 related peptides and five myelin basic protein preparations. Two principal determinants were identified, one of them sequential, the other nonsequential. The sequential determinant involved a peptide at or near the C-terminal end of S82 that could be blocked by an interchange of asparagine for glycine at the C terminus. The nonsequential determinant was dominant for a number of rabbit and rat antisera, both anti-S82 and anti-S81, and was shared not only by S81 and S82 but also by S8 and S80, i.e., the family of residues of bovine MBP sequence 69-83. Neither determinant was expressed in any of the myelin basic protein preparations, and the nonsequential determinant was not expressed in peptide sequences smaller than S8.

Effect of microheterogeneity on the structure and function of the myelin basic protein

The basic protein is a major component of central nerve myelin containing species with varying amounts of phosphorylation and deamidation in situ. Components of basic protein were separated on the basis of net charge. Differences in ionic interactions of components of basic protein in a two-phase partition system with beef brain phosphatidyl serine were small, but there was a tendency for less charged components to require less lipid to achieve the same degree of solubilization into the chloroform phase. Spectroscopic properties of the components were identical using the following techniques: far ultraviolet circular dichroism, difference ultraviolet spectroscopy, fluorescent determination of tyrosine pK values and fluorescence energy transfer. At alkaline pH transfer from Trp to Tyr O- was 25% efficient which indicates that the closest accepting tyrosine is approx. 10 A away (the closest fluorescent tyrosine is over 20 A away). In 6 M guanidinium chloride this transfer was abolished while difference spectra indicated that the aromatic amino acids became more exposed in this solvent. These results show that the basic protein has definite secondary structure but that is not affected by the post-translation modifications.

The dynamics of membrane structure

The membranes of living organisms are involved in many aspects of the life, growth and development of all cells. The predominant structural elements of these membranes are lipids and proteins and the basic strucvture of these molecules has been reviewed. The physical properties of the lipid constituents particularly their behavior in aqueous systems has led to the concepts of thermotropic and lyotropic mesomorphism; the interaction between different types of lipid molecules modulate this behavior. Interaction of phospholipids in aqueous systems with cholesterol, ions and drugs have been examined in this context. In addition a variety of model lipid-protein systems have been investigated and the implications of interactions between lipids and different proteins in biological membranes has been evaluated. This leads to a detailed consideration of the way lipids and proteins ae organized in cell membranes and contains an appraisal of the evidence supporting contemporary views of membrane structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Finally the biosynthesis, turnover and modulation of the properties of interacting membrane constituents is critically reviewed and possible ways of controlling the behavior of cells and organisms by altering the structural parameters of different membranes has been considered.

Failure of 5-hydroxytryptophan to increase lumbar MSR amplitude in rats paralyzed with experimental allergic encephalomyelitis

Doses of the 5-hydroxytryptamine precursor, 5-hydroxytryptophan, which markedly increased lumbar monosynaptic response (MSR) amplitude in control rats failed to do so in rats paralyzed with experimental allergic encephalomyelitis (EAE). However, lumbar MSR amplitude could be increased in EAE rats just as in control rats by tetanically stimulating the dorsal root. Post-tetanic potentiation of MSR amplitude occurred in the EAE paralyzed rats both prior to and following 5-hydroxytryptophan injection. It was concluded that, as has been reported for the peripheral system in EAE guinea pigs, central nervous system 5-hydroxytryptamine neurotransmission is impaired, at least in the lumbar spinal cord, in EAE rats with hindlimb paralysis.