Resolution of rat brain synaptic phosphoprotein B-50 into multiple forms by two-dimensional electrophoresis: evidence for multisite phosphorylation

Phosphoprotein B-50 was extracted from rat brain membranes by alkaline extraction and purified by ammonium sulphate precipitation and flat-bed isoelectric focusing. The purified protein shows microheterogeneity upon isoelectric focusing in a narrow pH gradient (pH 3.5-5.0). As visualized by two-dimensional gel electrophoresis, B-50 resolved into four clearly separated forms which differ slightly in isoelectric point. The forms are in part mutually convertible by exhaustive phosphorylation (using protein kinase C) and dephosphorylation (using Escherichia coli alkaline phosphatase). Proteolysis with Staphylococcus aureus protease yielded two radioactive peptides. Analysis of their molecular weights and the time course of their formation suggests that B-50 was cleaved at only one specific site. Our data indicate the presence of more than one phosphorylatable site. The possibility that the heterogeneity of B-50 was in part due to a glycoprotein nature of B-50 was studied extensively. However, none of the six different methods used revealed the presence of glyco-moieties in B-50.

Liquid-liquid extraction of membranes from calf brain using conventional and centrifugal counter-current distribution techniques

Neural membranes isolated from calf brain have been partitioned in aqueous two-phase systems containing dextran and polyethyleneglycol. When the partition was repeated several times, using counter-current distribution technique, the distribution of the membranes between the upper phase and the interface changed in a non-ideal manner and in favour of the interface. By using a centrifugal counter-current distribution device the time for the experiment could be reduced by a factor of 7-8 and the distribution was similar to what could be expected for ideally behaving membranes. The time-dependent change of the membranes is discussed in terms of aggregation and lateral membrane perturbations. Despite this effect a certain fractionation has been achieved as deduced from analysis of cholesterol content, opiate receptor activity and acetylcholinesterase activity along the counter-current distribution row of fractions. Compared to the starting material these activities were enriched some two-fold in certain fractions.

Amniotic fluid analysis in prenatal diagnosis of neural tube defects: a comparison between six biochemical tests supplementary to the measurement of amniotic fluid alpha-fetoprotein

Concanavalin A (con A) and lens culinaris agglutinin (LCA) microheterogeneity pattern of AFP (crossed affinity immunoelectrophoresis), alpha-2-macroglobulin and synaptic membrane protein D-2 (rocket immunoelectrophoresis) and qualitative (polyacrylamide gel electrophoresis) and quantitative (enzyme kinetic reaction rate) acetylcholinesterase were analysed in 87 consequtive samples from normal pregnancies and 37 abnormal samples (fetal neural tube defect or abdominal wall defect). Very few false positive results were obtained in normal pregnancies with any of the tests. In all cases of neural tube defects the correct result was obtained with qualitative acetylcholinesterase analysis, whereas only 2/3 of the abdominal wall defects were correctly predicted. Testing with con A or LCA was less optimal in neural tube defects, whereas all abdominal wall defects could be predicted correctly. Acetylcholinesterase in the quantitative test and protein D-2 did not decrease the rate of false results. Determination of the alpha-2-macroglobulin concentration performed well in the present study, but is not recommended because of the very high susceptibility to contamination of amniotic fluid with fetal or maternal blood.

Cross-reaction of anti-rat B-50: characterization and isolation of a "B-50 phosphoprotein" from bovine brain

Antibodies to the phosphoprotein B-50 of rat brain were used to trace cross-reacting brain proteins of vertebrates. With the SDS-gel-immunoperoxidase method, a cross-reacting protein (CP) of apparent Mr 53,000 was demonstrated in the homogenate and the synaptic plasma membrane fraction of bovine brain. Sequence 1-24 of adrenocorticotropin (ACTH1-24) (10(-5) M and 10(-4) M) inhibited endogenous phosphorylation of CP in synaptic plasma membranes. The protein was partially characterized and purified to homogeneity from bovine brain by procedures previously described for rat B-50. CP was enriched in ammonium sulfate precipitated protein (ASP) fractions and phosphorylated by an endogenous protein kinase. Two-dimensional gel analysis of bovine and rat ASP showed that the cross-reacting protein had an isoelectric point less acidic than B-50. Limited proteolysis by Staphylococcus aureus protease yielded a "peptide map" analogous to B-50. Two major fragments of Mr 30,000 and 17,000 were produced. In addition, CP exhibited other similarities to rat B-50: phosphorylation by rat brain protein kinase C, microheterogeneity observed after isoelectric focusing, and possibly degradation by endogenous proteolysis. Cross-reaction of proteins in brain homogenates of other mammalian species and of chicken was demonstrated: the Mr of the proteins ranged from 47,000 to 53,000. We conclude that (1) the cross-reacting bovine protein is a "B-50 protein," and (2) the Mr of the "B-50 protein" varies from species to species.

Concanavalin A binding glycoproteins in subcellular fractions from the developing rat cerebral cortex

Synaptic plasma membrane (SPM) and mitochondrial fractions were prepared from 3-50-day rat cerebral cortex and their purity assessed. The fractions were subjected to electrophoresis on slab gels, stained for protein, and overlaid with 125I-concanavalin A (ConA). ConA binding glycoproteins (CABGs) were revealed by autoradiography. In the SPM fraction CABGs of MW 25,000, 63,000, 80,000, 115,000, 174,000, and 239,000 increased while those of MW 47,000, 75,000, and 190,000 decreased developmentally. In the mitochondrial fraction, CABGs of MW 25,000, 44,000, 115,000 and 174,000 increased while those of 34,000, 43,000, 47,000, 51,000, 80,000, 107,000, and 195,000 decreased developmentally. CABGs of MW 32,000, 63,000, 88,000, 153,000, 190,000, and 239,000 appear to be unique to the SPM fraction and those of MW 34,000, 107,000, and 195,000 are unique to the mitochondrial fraction.

[Changes in the synaptosomal membranes in the chronic neurotization of rats]

A study was made of the changes in synaptosomal membranes and in some synaptic processes under the development of experimental neurosis in rats. Neurotic rats demonstrated changes in the protein/lipid correlation and in the interaction of the fluorescent ANS probe and synaptosomal membranes. This can be accounted for by an increase in the membrane water repellency. The activity of Na, K-ATPase remains unchanged. The rate of noradrenaline, serotonin, dopamine and GABA synaptosomal reverse uptake in neurotic rats was found to be increased.

Peripheral proteins of postsynaptic membranes from Torpedo electric organ identified with monoclonal antibodies

Highly purified postsynaptic membranes from Torpedo electric organ contain the acetylcholine receptor as well as other proteins. To identify synapse-specific components, we prepared monoclonal antibodies (mabs) to proteins extracted from the membranes with either lithium diiodosalicylate or alkaline treatment. 10 mabs specific for three different proteins were obtained. Seven mabs reacted with a major 43,000-mol-wt protein (43K protein). This protein is composed of isoelectric variants (pl = 7.2-7.8) and each of the mabs reacted with all of the variants. Analysis of these mabs by competition for binding to 43K protein and by reaction with proteolytic fragments of 43K protein in immunoblots showed that they recognize at least five different epitopes. Two mabs reacted with a protein of 90,000 mol wt (90K protein) and one with a protein of 58,000 mol wt composed of isoelectric variants (pl = 6.4-6.7) (58K protein). The 43K and 58K proteins appeared to co-purify with the receptor-containing membranes while the 90K protein did not. Immunofluorescence experiments indicated that the anti-43K mabs bind to the innervated face of Torpedo electrocytes and that a component related to the 43K protein is found at the rat neuromuscular junction. The anti-58K mab stained the innervated face, although rather weakly, while the anti-90K mabs reacted intensely with the non-innervated membrane. Thus, the 43K protein and possibly also the 58K protein are synaptic components while the 90K protein is predominantly nonsynaptic.

Identification and comparison of protein I in chick and rat forebrain

Protein I has been identified and compared in membranes prepared from chick and rat forebrain. Based upon five criteria known to characterize protein I, namely, (1) its ability to serve as a substrate for both the cyclic AMP-dependent protein kinase and (2) the Ca2+- dependent, calmodulin-requiring protein kinase, (3) its ability to be extracted from membranes at low pH, (4) its characteristic pattern of digestion by collagenase, and (5) its existence as a basic protein, we have determined that although protein I of rat brain consists of the usual doublet polypeptides Ia and Ib, only a single chick forebrain polypeptide is detectable which possesses protein I-like properties.

Regions of putative acetylcholine receptors at synaptic contacts between neurons maintained in culture and subsequently fixed in solutions containing tannic acid

Spinal cord neurons from 9-day chick embryos were maintained in culture for up to 35 days and then fixed in 4% cacodylate-buffered glutaraldehyde containing 2% tannic acid. After about 15 days in culture a small percentage of the synaptic specializations present were characterized by striking electron-dense striations averaging 15 nm in width, oriented perpendicular to the postsynaptic membrane. These structures increased in frequency with time in culture (to a maximum of about 10% of all synapses in the oldest cultures); they were asymmetrical, protruding approximately 8 nm into the synaptic cleft, and more deeply (approximately 15-18 nm), into the postsynaptic cytoplasm. On the basis of earlier work by Sealock (1980) they are interpreted as concentrations of acetylcholine receptors. Similar membrane differentiations were also seen associated with active-zone areas of a few presynaptic membranes, and the possibility that these represent presynaptic acetylcholine receptors is discussed. Additional observations reported are (1) the presence of striations resembling those seen at the postsynaptic membrane in the membranes of some postsynaptic vesicles, and (2) filamentous links between the striations and cytoskeletal elements of the postsynaptic cell.

Immunochemical and molecular differentiation of 43 000 molecular weight proteins associated with Torpedo neuroelectrocyte synapses

Synaptic membranes, highly enriched in nicotinic receptor, contain three 43 000 molecular weight (Mr) peripheral proteins (distinctive in their peptide mapping profiles and earlier designated v1, v2, and v 3) as well as the receptor alpha 2 beta gamma delta integral membrane subunits. Of the three proteins, only v1 is copurified with the membrane-bound receptor, while v2 and v3 are prominent cytosolic proteins, which are retained at significant levels in receptor-rich membranes during multistep centrifugation and affinity partitioning purification procedures [Gysin, R., Wirth, M., & Flanagan, S. D. (1981) J. Biol. Chem. 256, 11373-11376]. Peptide mapping analysis of Torpedo v3 and rabbit skeletal actin indicates that the two proteins are closely related. The enzymatic activity, creatine phosphokinase (EC 2.7.3.2), copurifies with v2 during chromatofocusing fractionation of the cytosol. The Torpedo electroplax form of creatine phosphokinase has an electrophoretic mobility identical with that of the mammalian skeletal muscle form of the enzyme. Upon release of the membrane-bound forms of v1, creatine phosphokinase, and actin by the action of mild alkali, v1 remains in a high molecular weight form. Dissociation of v1 into lower molecular weight species requires urea or sodium dodecyl sulfate (NaDodSO4). Preparation of essentially pure v1 was achieved by eluting the v1 protein spots directly from naDodSO4-isoelectric focusing gels loaded with alkali extracts derived from membranes highly enriched in nicotinic receptor. Amino acid compositions of the purified fractions indicate that v1 and Torpedo creatine phosphokinase have distinct amino acid compositions from each other and from that of actin.(ABSTRACT TRUNCATED AT 250 WORDS)

Low cerebrospinal fluid concentration of brain-specific protein D2 in patients with normal pressure hydrocephalus

The synaptic membrane glycoprotein D2 was measured in cerebrospinal fluid (CSF) and plasma in 13 patients with normal pressure hydrocephalus (NPH), in 14 patients with primary degenerative dementia of Alzheimer type (PDD), and in 24 patients without evidence of organic nervous disease (controls). Mean CSF D2 concentration was significantly lower in NPH patients: 299 +/- 48 ng/ml (SEM) (P less than 0.001) than in PDD patients: 658 +/- 50 ng/ml (SEM) and in controls 641 +/- 45 ng/ml (SEM). Plasma D2 concentrations were higher in PDD patients compared with those found in controls. Determination of CSF D2 concentrations might be of diagnostic value in discrimination between patients with NPH and PDD patients with enlarged ventricles associated with diffuse brain atrophy.

Characterization and localization of the Mr = 43,000 proteins associated with acetylcholine receptor-rich membranes

A protein of Mr = 43,000 (43K protein) is a major component of highly purified postsynaptic membranes isolated from Torpedo electric organ. It can be removed from these membranes by alkaline treatment or with 10 mM lithium diiodosalicylate, conditions which extract peripheral membrane proteins without solubilizing the acetylcholine receptor. Two-dimensional polyacrylamide gel electrophoresis of the lithium diiodosalicylate extract shows it to contain several major Mr = 43,000 components of isoelectric points between 7.0 and 8.0 and a minor component of approximately pI 5.6. The pI 5.6 polypeptide co-migrates with skeletal muscle actin on a two-dimensional gel and gives a peptide map pattern very similar to that of actin. The three major spots of pI 7.0-8.0 yield peptide maps which are indistinguishable from one another but quite different from that of actin. The membrane-bound forms of both the basic 43K protein and actin can be iodinated in a lactoperoxidase-catalyzed reaction only if the membrane vesicles are first permeabilized with saponin, a treatment which permits entry of macromolecules to the interior of the vesicles. An immunoblot of a two-dimensional gel shows that a rabbit antiserum made against alkaline extract reacts strongly with the basic 43K protein and to lesser extent with an acidic component of Mr = 55,000 but not with actin. Immunofluorescence studies have shown that this antiserum reacts with the innervated face of Torpedo electrocytes and recognizes a component of rat diaphragm muscle which is highly concentrated at the neuromuscular junction (Froehner, S.C., Gulbrandsen, V., Hyman, C., Jeng, A. Y., Neubig, R. R., and Cohen, J. B. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 5230-5234). Similar experiments on intact rat muscle indicate that, like the 43K protein of Torpedo postsynaptic membranes, the immunologically related component in mammalian muscle endplates is located on the cytoplasmic side of the postsynaptic membrane.

The purification and characterization of a Thy-1-like glycoprotein from chicken brain

We have purified from chicken forebrain a membrane glycoprotein that is enriched in purified synaptic membranes and has an apparent mol.wt. of 22 800 in 15% sodium dodecyl sulphate/polyacrylamide gels. This molecule was compared with rat and human brain Thy-1 glycoproteins purified by the same procedure in order to determine whether it could be a homologue of Thy-1. Although polyvalent heterologous antisera raised against the rat and chicken molecules showed no immunological cross-reactivity with the other glycoprotein, a great deal of physical and chemical similarity was demonstrated between the chicken glycoprotein and rat Thy-1. Their apparent molecular weights, subcellular localization and amino acid and amino sugar compositions are very similar. C.d. spectra show that both molecules contain predominantly a beta-sheet and structure with no detectable alpha-helix. Electrophoretic analysis of the CNBr-cleaved molecules under reducing and non-reducing conditions shows that both molecules contain intramolecular disulphide bridges. Taken together these results suggest that the chicken brain glycoprotein is an immunologically distinct homologue of the mammalian Thy-1 glycoproteins.

Chloride and calcium ions separate L-glutamate receptor populations in synaptic membranes

Cl-/Ca2+-dependent and Cl-/Ca2+-independent L-[3H]glutamate binding sites in rat brain synaptic membranes showed marked differences in their pharmacological properties. One site resembled L-2-amino-4-phosphonobutyrate (L-APB)-sensitive receptors and the other N-methyl-D-aspartate (NMDA) receptors. Inhibition studies demonstrated that L-aspartate was more potent at Cl-/Ca2+-independent than at Cl-/Ca2+-dependent sites although L-glutamate was of similar potency at both sites; the D-isomers of aspartate, glutamate and alpha-aminoadipate exhibited the opposite trend. Quisqualate and ibotenate showed high and low affinity inhibition components in the presence of Cl- and Ca2+, and only low affinity inhibition at Cl-/Ca2+-independent sites. For a series of alpha-amino-omega-phosphono carboxylic acids (propionate-heptanoate), peaks of inhibitory activity in the presence of Cl- and Ca2+ were shifted to l-carbon shorter homologues than in the absence of these ions. These data indicate that the ionic environment is of critical importance for the activity of different physiological receptor populations in vitro.

A simple and efficient method for solubilization of the dopamine receptor

The solubilization of dopamine receptors from bovine caudates was carried out with different detergents and detergent-salt combination. 0.25 M cholic acid: 1 M NaCl combination solubilized more effectively than the other detergents used. Solubilized receptors demonstrated the similar affinity and specificity as the membrane receptors. Solubilized receptors satisfied all the criteria of solubilization. Solubilized receptors were highly stable at 4 degrees C and freezing at -70 degrees C.

The benzodiazepine/GABA receptor complex: molecular size in brain synaptic membranes and in solution

The molecular size of the benzodiazepine (BZ) receptor in the synaptic membrane of brain cortex (bovine or rat) was determined by an improved version of the radiation inactivation method to be 220,000. An identical size was found simultaneously for the associated gamma-aminobutyric acid (GABA) receptor and for the component binding beta-carboline esters. It is proposed that all three activities reside in a single protein or protein complex in the membrane. The size in solution, after extraction into Triton X-100 medium from exhaustively washed membranes, was estimated by sedimentation constant (9.4S) and by gel filtration ( approximately 230,000 apparent MW), again with the BZ and GABA binding activities behaving identically. This size applies to the component that undergoes photoaffinity labelling by [3H]flunitrazepam in the membrane, and contains a 51,000 Mr polypeptide as the BZ-binding subunit. It is concluded that a protein complex or oligomer of 200,000-220,000 MW carries a class of BZ-binding sites and an associated class of GABAA sites.

Partial purification of presynaptic plasma membrane by immunoadsorption

During transmitter release, synaptic vesicle membrane is specifically inserted into the nerve terminal plasma membrane only at specialized sites or "active zones." In an attempt to obtain a membrane fraction enriched in active zones, we have utilized the electric organ of the marine ray. From this organ, a fraction enriched in nerve terminals (synaptosomes) was prepared by conventional means. These synaptosomes were bound to microscopic beads by an antiserum to purified electric organ synaptic vesicles (anti-SV). The success of this immunoadsorption procedure was demonstrated by increased specific activities of bead-bound nerve terminal cytoplasmic markers and decreased specific activities of markers for contaminating membranes. To obtain a presynaptic plasma membrane (PSPM) fraction, we lysed the bead-bound synaptosomes by hypoosmotic shock and sonication, resulting in complete release of cytoplasmic markers. When the synaptosomal fraction was surface-labeled with iodine before immunoadsorption, 10% of this label remained bead-bound after lysis, compared with 2% of the total protein, indicating an approximately fivefold enrichment of bead-bound plasma membrane. Concomitantly, the specific activity of bead-bound anti-SV increased approximately 30-fold, indicating an enrichment of plasma membrane which contained inserted synaptic vesicle components. This PSPM preparation is not simply synaptic vesicle membrane since two-dimensional electrophoresis revealed that the polypeptides of the surface-iodinated PSPM preparation include both vesicle and numerous nonvesicle components. Secondly, antiserum to the PSPM fraction is markedly different from anti-SV and binds to external, nonvesicle, nerve terminal components.

Gangliosides associated with microsomal subfractions of brain: comparison with synaptic plasma membranes

To study ganglioside distribution within subcellular components and test the hypothesis that they are localized at the nerve ending, microsomes and synaptic plasma membranes were isolated from young adult rat brains and compared with respect to ganglioside composition. These were shown to be heterogeneous preparations by fractionation on a discontinuous sucrose gradient into subfractions which had differing ganglioside concentrations. The highest ganglioside concentrations occurred in membranes banding at the 0.8M/1.0M and 1.0M/1.3M interfaces for both microsomes and synaptic plasma membranes. These subfractions had closely similar ganglioside concentrations and pattern distributions. In addition, the kinetics of ganglioside labeling following administration of [3H]-glucosamine were similar for the two preparations. The fact that microsomal subfractions representing heterogeneous mixtures of brain cell membranes showed close similarity to synaptosomal plasma membranes argues against localization of gangliosides at the nerve ending. These results, together with other lines of evidence, support the concept that gangliosides are distributed over large portions of the neuron (and perhaps other brain cells). Data concerning the labeling of gangliosides in different microsomal subfractions indicated a movement of label over time from the more dense to the less dense membranes, as was also noted for the glycoproteins in the same subfractions. Specific radioactivity of the gangliosides increased relative to that of the glycoproteins with time.

Purification of the synaptic membrane glycoprotein D2 from rat brain

D2 is a nervous-specific membrane protein enriched in fractions of synaptosomal membranes from rat brain. Recently, an immunochemical relationship between D2 and the chick cell adhesion molecule (CAM) has been demonstrated. There is reason to believe that D2 is involved in adhesion phenomena between neurites. The purpose of the present study was to purify and further characterize the D2 protein from rat brain. In the developed purification procedure synaptosomal membranes from rat brains were prepared and solubilized by means of non-ionic detergent. The subsequent purification steps were hydroxylapatite chromatography, wheat germ lectin affinity chromatography, gel filtration, and lysine affinity chromatography. The purified D2 was found to be enriched 240 times compared with the starting brain homogenate and 120 times compared with the synaptosomal membrane fraction. The recovery of D2 was 26% when the amount of D2 in the synaptosomal membrane fraction was set to 100%. The purified D2 antigen was used for production of monospecific rabbit antisera, and it was found to be composed of two polypeptides of apparent molecular weights 130,000 and 150,000, respectively.

Synaptic plasma membrane tubulin may be an integral constituent

Mild detergent extraction of chick brain synaptic plasma membranes followed by gel electrophoresis suggests that synaptic plasma membrane tubulin is an integral component. Although some of the synaptic plasma membrane tubulin might be aggregates, that possibility is not supported by the observation that tubulin aggregates that are added to synaptosomes before synaptic subfractionation do not partition with synaptic plasma membranes during membrane isolation.