Bovine peripheral nervous system myelin P2 protein: chemical and immunological characterization of the cyanogen bromide peptides

The fatty acid transport function of fatty acid-binding proteins

The intracellular fatty acid-binding proteins (FABPs) comprise a family of 14-15 kDa proteins which bind long-chain fatty acids. A role for FABPs in fatty acid transport has been hypothesized for several decades, and the accumulated indirect and correlative evidence is largely supportive of this proposed function. In recent years, a number of experimental approaches which more directly examine the transport function of FABPs have been taken. These include molecular level in vitro modeling of fatty acid transfer mechanisms, whole cell studies of fatty acid uptake and intracellular transfer following genetic manipulation of FABP type and amount, and an examination of cells and tissues from animals engineered to lack expression of specific FABPs. Collectively, data from these studies have provided strong support for defining the FABPs as fatty acid transport proteins. Further studies are necessary to elucidate the fundamental mechanisms by which cellular fatty acid trafficking is modulated by the FABPs.

A T cell epitope for experimental allergic neuritis is an amphipathic alpha-helical structure

The bovine P2 protein is known to produce experimental allergic neuritis (EAN) in Lewis rats. The longest region of amphipathic alpha-helix within the bovine P2 protein was identified as residues 61-72. A synthetic peptide representing this sequence was synthesized and shown to have the ability to (1) produce EAN in Lewis rats by direct sensitization, (2) produce a lymphoproliferative response in a P2-specific T cell line, and (3) stimulate a P2 protein-specific T cell line sufficiently to transfer EAN to naive recipient Lewis rats. Residues 61-72 is the shortest sequence thus far identified that will produce EAN in the Lewis rat and supports the contention that T cell determinants tend to be amphipathic alpha-helices.

A T cell epitope for experimental allergic neuritis

A synthetic peptide representing residues 57-81 of the bovine P2 protein produced severe paralytic experimental allergic neuritis (EAN) in Lewis rats. Peptide 57-81 could also be used to stimulate a P2 protein-specific T cell line to transfer paralytic EAN to naive recipient rats. A smaller peptide representing residues 60-81 produced a milder form of clinical disease. Residues 60-81 are the shortest peptide sequence thus far described which can produce clinical EAN. The structural predictions for the sequence represented by these peptides support the contention that T cell antigenic sites tend to be amphipathic alpha-helical structures.

Bovine P2 myelin basic protein crystallizes in three different forms

P2 protein is a minor component of the myelin membrane. We have crystallized this protein for high-resolution crystallographic study. Three crystal morphologies are available. Two of them are from ammonium sulfate, and one is from polyethyleneglycol (PEG). The unit cell of the most suitable crystals from PEG 4000 has the dimensions a = 91.3 A, b = 99.8 A, c = 56.0 A; is of space group P2(1)2(1)2(1); and contains up to four molecules per asymmetric unit. The limit of resolution is 2.7 A.

Myelin-associated glycoprotein and related glycoconjugates in developing cat peripheral nerve: a correlative biochemical and morphometric study

The expression and accumulation of the myelin-associated glycoprotein (MAG) and other glycoconjugates have been studied during myelination in the developing cat peripheral nervous system. The glycoconjugates studied have in common a similar carbohydrate determinant which is bound by many antibodies, including the mouse monoclonal antibody HNK-1, and human IgM paraproteins from patients with neuropathy. In addition to MAG, the reactive glycoconjugates include a 60-kilodalton (kD) glycoprotein and a group of 20-26 kD glycoproteins, as well as a group of recently identified acidic glycolipids, the major one of which is sulfate-3-glucuronyl paragloboside (SGPG). The accumulation of these glycoproteins and glycolipids is compared with the established myelin proteins P0, P1, and P2 and with morphometric indices of myelin volume and axonal perimeter. The study demonstrates that MAG appears and accumulates very early during myelination, being present at 15% of the maximum level prior to the appearance of P0, and at 80% of the maximum level when P0 is at 30% of its maximum level. In the adult, the level of MAG falls to 60% maximum. The 60 kD and 20-26 kD glycoproteins accumulate at the same time as or later than P0, suggesting that they are either compact myelin proteins or in membranes closely associated with compact myelin. SGPG accumulates with P0 early in myelination, but falls to 60% of maximum in the adult. By comparing biochemical and morphometric data, we demonstrate that P0 and other compact myelin proteins accumulate synchronously with the increase in myelin area. MAG accumulation, however, is closely related to changes in axonal perimeter, consistent with a predominant localization of MAG to the periaxonal membranes in the peripheral nervous system.

Crystallization of P2 myelin protein

Single crystals of bovine P2 myelin protein have been grown in polyethylene glycol 4000 by the hanging-drop vapor diffusion method. Crystals belonging to space group P2(1)2(1)2(1) with cell dimensions a = 91.8 A, b = 99.5 A, c = 56.5 A (1 A = 0.1 nm). The diffraction pattern extends to better than 2.3 A resolution.

The secondary structure of myelin P2 protein derived by secondary structure prediction methods, circular dichroism, and 400-MHz 1H-NMR spectroscopy: implications for tertiary structure

The various methods used to study the secondary and tertiary structure of myelin P2 protein, and one of its peptides (CN1), in aqueous solution, indicate that the native protein contains a significant fraction of alpha-helix, suggesting that the current prediction of an all-beta tertiary structure requires revision.

Cell-mediated immunity to bovine P2 protein and neuritogenic synthetic peptide in experimental allergic neuritis

Cellular reactivity to bovine P2 protein (P2) and its two synthetic peptides, SP66-78 and SP70-78, was serially examined by the lymphocyte proliferation test in animals with experimental allergic neuritis (EAN). SP66-78 and SP70-78 correspond to residues 66-78 and 70-78 of bovine P2. Proliferative response to SP66-78 as well as P2 appeared at day 7 before the onset of EAN and was clearly manifested at day 14 in the active stage, thereafter disappearing in the stable stage, whereas no response to SP70-78 was detected during the course of the disease. These results suggest that cell-mediated immune response to P2 and the specific part residues 66-78 of P2 play an important role in the pathogenesis of EAN.

Lipid content of swine influenza and other vaccines

An analysis of the lipids in swine influenza vaccines was performed, comparing six different lots of swine influenza, other influenza and noninfluenza vaccines. Cholesterol content and phospholipid content varied greatly, but there were no major differences between the types of vaccines. Appreciable amounts of phosphatidylethanolamine were found in only one swine influenza vaccine. The major phospholipids of influenza vaccines were phosphatidylcholine, sphingomyelin and phosphatidic acid. A detectable amount of phosphatidylserine was not found in any swine influenza vaccine, but was present in two of three nonswine influenza vaccines. Only two of six swine influenza vaccines showed trace amounts (less than 0.5 microgram/ml) of ganglioside (GM3). However, larger quantities of galactocerebroside were found (2.24-6.43 micrograms/ml) in all influenza vaccines examined, including swine influenza vaccines.

Cellular hypersensitivity to nervous antigens in Guillain-Barré syndrome

Cell-mediated immune responses to various nervous antigens were examined in 12 cases of Guillain-Barré syndrome (GBS), 24 cases of noninflammatory peripheral neuropathy (NIPN), and 18 cases of degenerative disorders of central nervous system (CNSDD), using the lymphocyte-transformation technique. Cellular hypersensitivity to bovine P2 protein (P2) and a synthetic peptide, SP66-78, corresponding to the residues 66-78 of P2, was detected in about two-thirds of GBS cases, especially in the active or improving stages, but not in NIPN and CNSDD. The lymphocytes sensitized to these nervous antigens might play an important role in the pathogenesis of GBS.

Degradation of bovine P2 protein by bovine brain cathepsin D

Bovine brain cathepsin D cleaved bovine P2 protein to produce three major and several minor peptides. The major P2 peptides formed were shown by amino acid analysis and partial sequencing to be peptides 17-54, 20-58 and 65-131 with the latter predominating. In preliminary experiments, P2 peptide 65-131 did not induce experimental allergic neuritis in Lewis rats in equimolar amounts to the neuritogenic P2.

Lipid binding activities of the P2 protein in peripheral nerve myelin

Lipid binding activities of the P2 protein in peripheral nerve myelin were examined using retinoic acid, retinol and oleic acid as ligands. The P2 protein showed the specific binding affinity to both of retinoic acid and retinol. The binding site of these ligands was suggested to be similar. In addition, the high binding activity of the P2 protein with oleic acid was also observed. The ligands specificities of the P2 protein are clearly different from those of cellular retinoic acid binding protein (CRABP), cellular retinol binding protein (CRBP), and Z protein. In amino terminal sequence, however, the P2 protein contained considerable homologous structure to these lipid binding proteins. Therefore, the P2 protein and these lipid binding proteins may belong to a family of structurally related proteins evolved from a common ancestral gene.

A general model of the P2 protein of peripheral nervous system myelin based on secondary structure predictions, tertiary folding principles, and experimental observations

The amino acid sequence of the P2 protein of peripheral myelin was analyzed with regard to regions of probable alpha-helix, beta-structure, beta-turn, and unordered conformation by means of several algorithms commonly used to predict secondary structure in proteins. Because of the high beta-sheet content and virtual absence of alpha-helix shown by the circular dichroic spectra of the protein, a bias was introduced into the algorithms to favor the beta-structure over the alpha-helical conformation. In order to define those beta-sheet residues that could lie on the external hydrophilic surface of the protein and those that could lie in its hydrophobic interior, the predicted beta-strands were examined for charged and uncharged amino acids located at alternating positions in the sequence. The sequential beta-strands in the predicted secondary structure were then ordered into beta-sheets and aligned according to generally accepted tertiary folding principles and certain chemical properties peculiar to the P2 protein. The general model of the P2 protein that emerged was a "Greek key" beta-barrel, consisting of eight antiparallel beta-strands with a two-stranded ribbon of antiparallel beta-structure emerging from one end. The model has an uncharged, hydrophobic core and a highly hydrophilic surface. The two Cys residues, which form a disulfide, occur in a loop connecting two adjacent antiparallel strands. Two hydrophilic loops, each containing a cluster of acidic residues and a single Phe, protrude from one end of the molecule. The general model is consistent with many of the properties of the actual protein, including the relatively weak nature of its association with myelin lipids and the positions of amino acid substitutions. Alternative beta-strand orderings yield three specific models having different interstrand connections across the barrel ends.

Prevention of experimental allergic neuritis in the Lewis rat with bovine P2 protein

Protective doses of bovine P2 protein (5, 15 or 50 micrograms) in incomplete Freund's adjuvant (IFA) were administered to Lewis rats and were followed 2, 4 or 10 weeks later by challenging doses of either 250 micrograms bovine P2 or 2.5 mg bovine PNS myelin in complete Freund's adjuvant (CFA). Protection from experimental allergic neuritis (EAN) could be achieved with a single dose of 5 micrograms of P2 in IFA. There was little difference between prophylactic 5 micrograms and 15 micrograms doses of P2. The degree of protection depended upon the interval between protective innoculation and challenge. Protection was partial at 2 weeks and maximal at 4 weeks at which time there was complete protection against P2-induced EAN and less complete protection from myelin-induced disease. Complete protection at 4 weeks from myelin-induced EAN was achieved with a 50 micrograms dose. Protection lasted for at least 10 weeks (the longest interval assessed) and was complete with respect to P2-induced EAN. Partial protection was observed in myelin-challenged animals after 10 weeks with the level of protection greater than that observed after 2 weeks.

Studies with antisera against peripheral nervous system myelin and myelin basic proteins. I. Effects of antiserum upon living cultures of nervous tissue

We studied the effects of antiserum against rat peripheral nervous system (PNS) myelin, rat or chicken central nervous system myelin basic protein (BP), or rabbit P2 protein from PNS myelin on myelinated cultures containing only rat dorsal root ganglion neurons and Schwann cells. While anti-PNS myelin serum consistently produced segmental PNS demyelination, anti-BP serum and anti-P2 serum did not. The culture results suggest that the myelin PNS proteins P1 (identical to basic protein from central nervous system myelin) and P2 are not exposed on the extracellular surfaces of myelin-related Schwann cells in tissue culture.

Neuritogenic determinant of bovine P2 protein in peripheral nerve myelin

Experimental allergic neuritis (EAN) is an experimentally produced demyelinating disease of peripheral nervous system. Several peptides of bovine P2 protein were tested for neuritogenic activity in Lewis rats. The hexacosapeptide CiT4 (residues 53--78 of bovine P2 protein) showed the highest neuritogenic activity among the peptides tested. The nonapeptide (residues 70--78) and the tridecapeptide (residues 66--78) were synthesized using the liquid phase peptide synthesis technique. The tridecapeptide showed mild, but definite activity in inducing EAN in the rats, while the nonapeptide was inactive. The localization of the neuritogenic determinant of bovine P2 protein in Lewis rats is discussed.

Conformation of bovine nerve root P2 protein: characteristics of the molecule from circular dichroism spectra

Circular dichroism (CD) was used to study the conformations of bovine nerve root P2 basic protein, its reduced and carboxymethylated derivative (RCM-P2), and its large cyanogen bromide fragment (CN1). Data in the far UV show that both the parent protein and RCM-P2 have conformations dominated by a large amount of beta structure. However, the CN1 peptide appears to exist in a largely unordered conformation. Since CN1 lacks short (20 residue) amino- and carboxy-terminal segments of the P2 protein, the spectral data suggest that these regions are important for determining and/or maintaining folding of the P2 protein in aqueous solutions. The P2 protein was found to have a distinctive CD spectrum in the near UV. The characteristics of molar ellipticities indicate that the spectrum contains significant contributions from tyrosine residues, and that these contributions suggest different environments for the two tyrosines in P2 protein. Both environments depend on protein conformation, since CD side chain absorptions are lost when P2 protein is denatured with 5 M urea.

Structure of bovine P2 basic protein: sequence of a carboxyterminal segment that is a neuritogen in rabbits

The sequence of the carboxyterminal 18 amino acids released by cyanogen bromide digestion of the bovine P2 protein was determined. It has several interesting structural and immunological properties. It contains the only two half-cystines in the molecule that have the capacity to form an intrachain disulfide bond. Using the rabbit as a test animal, this carboxyterminal peptide was capable of producing experimental allergic neuritis. The sequence of this peptide is Val-Val-Glu-Cys-Lys-Met-Lys-Asp-Val-Val-Cys-Thr-Arg-Ile-Tyr-Glu-Lys-Val.

The protein antigens of peripheral nerve myelin

Peripheral nervous system (PNS) tissue contains a variety of proteins, lipids, and carbohydrates that may serve as immunogens in proving immune responses, as antigens participating in immunological reactions, or as both types of agents. Three proteins P0, P1, and P2, account for approximately 70% of PNS myelin proteins. P0 is the major PNS myelin protein and is restricted to the PNS. P1 is similar to, if not identical with, myelin basic protein, the component of central nervous system myelin which induces experimental allergic encephalomyelitis. P2 has neuritogenic properties for inducing experimental allergic neuritis and may be involved in immune-mediated PNS myelin injury in humans. The complete amino acid sequence for P2 has recently been delineated, and its neuritogenic, immunogenic, and antigenic features can now be further characterized.

Bovine P2 protein: sequence at the NH2-terminal of the protein

Sequence data from key fragments of the P2 protein established the order of cyanogen bromide (CNBr) peptides in the structure of the protein and the primary structure for approximately one-half of the molecule. Data were obtained from the three tryptic peptides of blocked NH2-terminal CNBr peptide (CN3), the large CNBr peptide of P2 protein (CN1), and a fragment obtained from P2 by cleavage at tryptophan with 2-(2-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine. This last fragment was found to contain an over-lapping sequence that proved the juxtaposition of CN1 and CN3 in P2 protein. Thus, based on this fact and the characteristics of the CNBr peptides, the P2 structure is composed of CNBr peptides in the order: CN3-CN1-CN2(Val)-CN2(Lys). A comparison was made between the partial sequence of P2 protein and the equivalent portion of the structure of bovine myelin basic protein. The structures of these two proteins were found to be distinctly different although certain similarities are found.