A quantitative dot-immunobinding assay for proteins using nitrocellulose membrane filters

Isolation of Synaptic Vesicles from Mammalian Brain

Synaptic vesicles (SVs) store neurotransmitters and undergo a fine-tuned regulatory and dynamic cycle of exo- and endocytosis, which is essential for neurotransmission at chemical synapses. The development of protocols for isolating SVs from biological extracts was a fundamental accomplishment since it allowed for characterizing the molecular properties of SVs using biochemical methods. In this chapter, we describe a modified procedure for isolating SVs from a few g of rodent brain and that can be completed within ~12 h. The protocol involves the preparation of isolated nerve terminals from which SVs are released by osmotic shock and then enriched via various centrifugation steps, followed by size exclusion chromatography as final purification step. The final vesicle fraction is 22-fold enriched in SVs over the starting material, and the final yield of SVs obtained using this protocol is approximately 20 μg of protein per gram of mouse brain. The degree of contamination by other organelles and particles monitored by morphology and immunolabeling compares well with that of the classical protocols.

Giving names to the actors of synaptic transmission: The long journey from synaptic vesicles to neural plasticity

More than a scientific paper or a review article, this is a remembrance of a unique time of science and life that the authors spent in Paul Greengard's laboratory at the Rockefeller University in New York in the 1980s and 1990s, forming the so-called synaptic vesicle group. It was a time in which the molecular mechanisms of synaptic transmission and the nature of the organelles in charge of storing and releasing neurotransmitter were just beginning to be understood. It was an exciting time in which the protein composition of synaptic vesicles started to be identified. It turned out that the interactions of synaptic vesicle proteins with the cytoskeleton and the presynaptic membrane and their modulation by protein phosphorylation represented an essential network regulating the efficiency of neurotransmitter release and thereby synaptic strength and plasticity. This is also a description of the distinct scientific journeys that the three authors took on going back to Europe and how they were strongly influenced by the generous and outstanding mentorship of Paul Greengard, his genuine interest in their lives and careers and the life-long friendship with him.

Comparative synaptosome imaging: a semi-quantitative method to obtain copy numbers for synaptic and neuronal proteins

Protein copy numbers can be measured by biochemical methods ranging from quantitative Western Blotting to several mass spectrometry approaches. Such methods only provide average copy numbers, obtained over large cell numbers. However, copy number estimates for single cells or single organelles could be obtained by combining biochemical characterizations with an imaging approach. We performed this here for synaptic proteins, in a protocol that we termed comparative synaptosome imaging for semi-quantitative copy numbers (CosiQuant). In brief, in CosiQuant we immunostain in parallel biochemically-characterized synaptosomes, for which we have already determined the average protein copy numbers, and the samples of interest (such as neuronal cultures). We then derive the copy numbers in the samples of interest by comparing the immunofluorescence intensities. We measured the intensities not only in arbitrary fluorescence units, but also as numbers of antibodies per synaptosome, for a large number of targets. This implies that other groups can immediately apply CosiQuant for these targets, by simply estimating the number of antibodies per structure of interest. CosiQuant should therefore be a useful addition to the growing set of imaging techniques for synaptic neuroscience.

Small-scale isolation of synaptic vesicles from mammalian brain

Synaptic vesicles (SVs) are essential organelles that participate in the release of neurotransmitters from a neuron. Biochemical analysis of purified SVs was instrumental in the identification of proteins involved in exocytotic membrane fusion and neurotransmitter uptake. Although numerous protocols have been published detailing the isolation of SVs from the brain, those that give the highest-purity vesicles often have low yields. Here we describe a protocol for the small-scale isolation of SVs from mouse and rat brain. The procedure relies on standard fractionation techniques, including differential centrifugation, rate-zonal centrifugation and size-exclusion chromatography, but it has been optimized for minimal vesicle loss while maintaining a high degree of purity. The protocol can be completed in less than 1 d and allows the recovery of ∼150 μg of vesicle protein from a single mouse brain, thus allowing vesicle isolation from transgenic mice.

Gene expression of pigment-binding proteins of the bacterial photosynthetic apparatus: Transcription and assembly in the membrane of Rhodopseudomonas capsulata

Lowering of oxygen partial pressure in chemotrophic cultures or reduction of light intensity in phototrophic cultures of Rhodopseudomonas capsulata induced formation of the photosynthetic apparatus. A maximum of mRNA coding for the reaction center (RC) and the light-harvesting 1 B870 antenna complex polypeptides occurred 30 min after induction. Maximal expression of mRNA for B800-B850 antenna proteins appeared with a lag time of about 25 min after RC/B870 mRNA. Pigment-binding polypeptides were inserted into the membrane immediately after mRNA synthesis. It is concluded that the delayed formation of the B800-B850 complex compared to the RC and the B870 complex is caused by sequential expression of the corresponding genes. Biological activity of pigment-protein complexes increased after the incorporation of their polypeptides parallel to the maximum of bacteriochlorophyll synthesis. Studies on mutant strains defective in the formation of pigment-protein complexes suggested that pigment synthesis is of importance for assembly of stable complexes.

Developmentally regulated expression of the bean beta-phaseolin gene in tobacco seed

Recombinant phage lambda177.4 contains a gene for beta phaseolin, a major storage glycoprotein of French bean seed. A 3.8-kilobase Bgl II-BamHI fragment containing the entire 1700-base-pair coding region, together with 863 base pairs of 5' and 1226 base pairs of 3' flanking sequence, was inserted into the A66 Ti plasmid of Agrobacterium tumefaciens and used to transform tobacco. The level of phaseolin in the seeds of plants regenerated from cloned tissue was 1000-fold higher than in other tissues. The molecular weight of the phaseolin RNA transcript in tobacco seeds was identical to that found in bean seeds. The phaseolin protein in tobacco seed was glycosylated and appeared to undergo removal of the signal peptide. However, a large proportion of the phaseolin was cleaved into discrete peptides. These same peptides were formed as phaseolin was degraded during tobacco seed germination. The phaseolin gene appeared to be inserted as a single copy, and the proportion of phaseolin per genome copy in tobacco seeds (up to 3% of the total embryo proteins) resembled that in the bean seeds (40% of total seed protein, expressed from about 14 copies per diploid genome). Furthermore, the transplanted gene was turned on during tobacco seed development, and its protein product, phaseolin, was localized in the embryonic tissues. Finally, the phaseolin gene was inherited as a Mendelian dominant trait in tobacco.

Identification of a unique isoform of 1-aminocyclopropane-1-carboxylic acid synthase by monoclonal antibody

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.4.1.14) is a key enzyme regulating ethylene biosynthesis in higher plants. A monoclonal antibody (mAb T20C) that immunoprecipitates the ACC synthase activity from tomato pericarp tissue extracts revealed that mAb T20C immunodecorates an approximately 67-kDa polypeptide. On isoelectric focusing gels, ACC synthase activity in cell-free preparations was resolved into three distinct activity peaks with pI values 5.3, 7, and 9. mAb T20C specifically recognized the pI 7 form of the enzyme on electrophoretic transfer (Western) blots. When analyzed by sodium dodecyl sulfate gel electrophoresis under reducing conditions, the eluted pI 7 form was confirmed to migrate as a polypeptide of 67 kDa. The 67-kDa pI 7 isoform is a previously undescribed form of ACC synthase.

Mechanism by which contact with plant cuticle triggers cutinase gene expression in the spores of Fusarium solani f. sp. pisi

Spores of the phytopathogenic fungus Fusarium solani f. sp. pisi were shown to produce the extracellular enzyme, cutinase, only when cutin or cutin hydrolysate was added to the spore suspension. Dihydroxy-C(16) acid and trihydroxy-C(18) acid, which are unique cutin monomers, showed the greatest cutinase-inducing activity. Experiments with several compounds structurally related to these fatty acids suggested that both a omega-hydroxyl and a midchain hydroxyl are required for cutinase-inducing activity. Cutinase appeared in the medium 30-45 min after the addition of the inducers to the spore suspension, and the activity level increased for 6 hr. Addition of cycloheximide (5 mug/ml) completely inhibited cutinase production, suggesting that protein synthesis was involved in the increase of cutinase activity. Immunoblot analysis with rabbit antibodies prepared against cutinase showed that cutinase protein increased in parallel with the increase in enzyme activity. Measurement of cutinase-specific RNA levels by dot-blot hybridization with (32)P-labeled cutinase cDNA showed that the cutinase gene transcripts could be detected within 15 min after addition of the inducers. Addition of exogenous cutinase greatly enhanced the level of cutinase gene transcripts induced by cutin. These results strongly suggest that the fungal spore senses that it is in contact with the plant by the production of small amounts of cutin monomers catalyzed by the low level of cutinase carried by the spore and that these monomers induce the synthesis of cutinase needed for penetration of the fungus into the plant.

Biomineralization: Functions of calmodulin-like protein in the shell formation of pearl oyster

Calmodulin-like protein (CaLP) was believed to be involved in the shell formation of pearl oyster. However, no further study of this protein was ever performed. In this study, the in vitro crystallization experiment showed that CaLP can modify the morphology of calcite. In addition, aragonite crystals can be induced in the mixture of CaLP and a nacre protein (at 16 kDa), which was detected and purified from the EDTA-soluble matrix of nacre. These results agreed with that of immunohistological staining in which CaLP was detected not only in the organic layer sandwiched between nacre (aragonite) and the prismatic layer (calcite), but also around the prisms of the prismatic layer. Take together, we concluded that (1) CaLP, as a component of the organic layer, can induce the nucleation of aragonite through binding with the 16-kDa protein, and (2) CaLP may regulate the growth of calcite in the prismatic layer.

Molecular anatomy of a trafficking organelle

Membrane traffic in eukaryotic cells involves transport of vesicles that bud from a donor compartment and fuse with an acceptor compartment. Common principles of budding and fusion have emerged, and many of the proteins involved in these events are now known. However, a detailed picture of an entire trafficking organelle is not yet available. Using synaptic vesicles as a model, we have now determined the protein and lipid composition; measured vesicle size, density, and mass; calculated the average protein and lipid mass per vesicle; and determined the copy number of more than a dozen major constituents. A model has been constructed that integrates all quantitative data and includes structural models of abundant proteins. Synaptic vesicles are dominated by proteins, possess a surprising diversity of trafficking proteins, and, with the exception of the V-ATPase that is present in only one to two copies, contain numerous copies of proteins essential for membrane traffic and neurotransmitter uptake.

Use of immunodotting to select the desorption agent for immunochromatography

In immunochromatography, a technique of increasing use, the sample containing the antigen (Ag) to be purified or determined is introduced into a chromatographic column containing an antibody (Ab) bound to the packing material. The antigen is retained based on antigen-antibody recognition. To reuse the immunocolumn for subsequent assays, the antigen has to be eluted without causing irreversible damage of antibodies. Selection of conditions for performing immunochromatography is usually made by trial and error. This way of working is time consuming and it may ruin the column. In this article, the feasibility of using immunodotting to select the conditions to be employed in one immunochromatographic assay is shown. An immunodotting method is developed to select the best desorption agent for an enzyme-linked immunoaffinity chromatography (ELIAC) assay to determine beta-lactoglobulin (beta-LG). The effect of several factors on the immunodotting performance is studied. The way of performing solvent exchange to treat the antibody with different solutions considered as potential desorption agents to check their effect is shown. Effectiveness of the solution chosen by immunodotting (4 M MgCl(2) in 20 mM Tris, pH 5.9) as desorption agent is demonstrated by immunochromatographic assays. The immunodotting and solvent exchange methods developed should be useful to choose solvents and conditions for any other kind of assay.

Identification of synapsin I peptides that insert into lipid membranes

The synapsins constitute a family of synaptic vesicle-associated phosphoproteins essential for regulating neurotransmitter release and synaptogenesis. The molecular mechanisms underlying the selective targeting of synapsin I to synaptic vesicles are thought to involve specific protein-protein interactions, while the high-affinity binding to the synaptic vesicle membrane may involve both protein-protein and protein-lipid interactions. The highly hydrophobic N-terminal region of the protein has been shown to bind with high affinity to the acidic phospholipids phosphatidylserine and phosphatidylinositol and to penetrate the hydrophobic core of the lipid bilayer. To precisely identify the domains of synapsin I which mediate the interaction with lipids, synapsin I was bound to liposomes containing the membrane-directed carbene-generating reagent 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine and subjected to photolysis. Isolation and N-terminal amino acid sequencing of 125I-labelled synapsin I peptides derived from CNBr cleavage indicated that three distinct regions in the highly conserved domain C of synapsin I insert into the hydrophobic core of the phospholipid bilayer. The boundaries of the regions encompass residues 166-192, 233-258 and 278-327 of bovine synapsin I. These regions are surface-exposed in the crystal structure of domain C of bovine synapsin I and are evolutionarily conserved among isoforms across species. The present data offer a molecular explanation for the high-affinity binding of synapsin I to phospholipid bilayers and synaptic vesicles.

Identification of synapsin I peptides that insert into lipid membranes

The synapsins constitute a family of synaptic vesicle-associated phosphoproteins essential for regulating neurotransmitter release and synaptogenesis. The molecular mechanisms underlying the selective targeting of synapsin I to synaptic vesicles are thought to involve specific protein-protein interactions, while the high-affinity binding to the synaptic vesicle membrane may involve both protein-protein and protein-lipid interactions. The highly hydrophobic N-terminal region of the protein has been shown to bind with high affinity to the acidic phospholipids phosphatidylserine and phosphatidylinositol and to penetrate the hydrophobic core of the lipid bilayer. To precisely identify the domains of synapsin I which mediate the interaction with lipids, synapsin I was bound to liposomes containing the membrane-directed carbene-generating reagent 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine and subjected to photolysis. Isolation and N-terminal amino acid sequencing of 125I-labelled synapsin I peptides derived from CNBr cleavage indicated that three distinct regions in the highly conserved domain C of synapsin I insert into the hydrophobic core of the phospholipid bilayer. The boundaries of the regions encompass residues 166-192, 233-258 and 278-327 of bovine synapsin I. These regions are surface-exposed in the crystal structure of domain C of bovine synapsin I and are evolutionarily conserved among isoforms across species. The present data offer a molecular explanation for the high-affinity binding of synapsin I to phospholipid bilayers and synaptic vesicles.

The domain of brain beta-spectrin responsible for synaptic vesicle association is essential for synaptic transmission

We have examined the interaction between synapsin I, the major phosphoprotein on the membrane of small synaptic vesicles, and brain spectrin. Using recombinant peptides we have localized the synapsin I attachment site upon the beta-spectrin isoform betaSpIISigmaI to a region of 25 amino acids, residues 211 through 235. This segment is adjacent to the actin binding domain and is within the region of the betaSpIISigmaI that we previously predicted as a candidate synapsin I binding domain based upon sequence homology. We used differential centrifugation techniques to quantitatively assess the interaction of spectrin with synaptic vesicles. Using this assay, high affinity saturable binding of recombinant betaSpIISigmaI proteins was observed with synaptic vesicles. Binding was only observed when the 25 amino acid synapsin I binding site was included on the recombinant peptides. Further, we demonstrate that antibodies directed against 15 amino acids of the synapsin I binding domain specifically blocked synaptic transmission in cultured hippocampal neurons. Thus, the synapsin I attachment site on betaSpIISigmaI spectrin comprises a approximately 25 amino acid segment of the molecule and interaction of these two proteins is an essential step for the process of neurotransmission.

Immunoisolation of GABA-specific synaptic vesicles defines a functionally distinct subset of synaptic vesicles

Synaptic vesicles from mammalian brain are among the best characterized trafficking organelles. However, so far it has not been possible to characterize vesicle subpopulations that are specific for a given neurotransmitter. Taking advantage of the recent molecular characterization of vesicular neurotransmitter transporters, we have used an antibody specific for the vesicular GABA transporter (VGAT) to isolate GABA-specific synaptic vesicles. The isolated vesicles are of exceptional purity as judged by electron microscopy. Immunoblotting revealed that isolated vesicles contain most of the major synaptic vesicle proteins in addition to VGAT and are devoid of vesicular monoamine and acetylcholine transporters. The vesicles are 10-fold enriched in GABA uptake activity when compared with the starting vesicle fraction. Furthermore, glutamate uptake activity and glutamate-induced but not chloride-induced acidification are selectively lost during immunoisolation. We conclude that the population of GABA-containing synaptic vesicles is separable and distinct from vesicle populations transporting other neurotransmitters.

Immunoisolation of GABA-specific synaptic vesicles defines a functionally distinct subset of synaptic vesicles

Synaptic vesicles from mammalian brain are among the best characterized trafficking organelles. However, so far it has not been possible to characterize vesicle subpopulations that are specific for a given neurotransmitter. Taking advantage of the recent molecular characterization of vesicular neurotransmitter transporters, we have used an antibody specific for the vesicular GABA transporter (VGAT) to isolate GABA-specific synaptic vesicles. The isolated vesicles are of exceptional purity as judged by electron microscopy. Immunoblotting revealed that isolated vesicles contain most of the major synaptic vesicle proteins in addition to VGAT and are devoid of vesicular monoamine and acetylcholine transporters. The vesicles are 10-fold enriched in GABA uptake activity when compared with the starting vesicle fraction. Furthermore, glutamate uptake activity and glutamate-induced but not chloride-induced acidification are selectively lost during immunoisolation. We conclude that the population of GABA-containing synaptic vesicles is separable and distinct from vesicle populations transporting other neurotransmitters.

Calcium transients in single fibers of low-frequency stimulated fast-twitch muscle of rat

Ca(2+) transients were investigated in single fibers isolated from rat extensor digitorum longus muscles exposed to chronic low-frequency stimulation for different time periods up to 10 days. Approximately 2.5-fold increases in resting Ca(2+) concentration ([Ca(2+)]) were observed 2 h after stimulation onset and persisted throughout the stimulation period. The elevated [Ca(2+)] levels were in the range characteristic of slow-twitch fibers from soleus muscle. In addition, we noticed a transitory elevation of the integral [Ca(2+)] per pulse with a maximum ( approximately 5-fold) after 1 day. Steep decreases in rate constant of [Ca(2+)] decay could be explained by an immediate impairment of Ca(2+) uptake and, with longer stimulation periods, by an additional loss of cytosolic Ca(2+) binding capacity resulting from a decay in parvalbumin content. A partial recovery of the rate constant of [Ca(2+)] decay in 10-day stimulated muscle could be explained by an increasing mitochondrial contribution to Ca(2+) sequestration.

Placental restriction alters adrenal medullary development in the midgestation sheep fetus

The aims of this study were to determine whether placental restriction (PR) alters the pattern of localization of the catecholamine-synthesizing enzymes, dopamine-beta-hydroxylase and phenylethanolamine N-methyltransferase, and enkephalin (ENK)-containing peptides in the adrenal gland of the midgestation sheep fetus. We also determined the effect of PR on the content and profile of the molecular mass forms of ENK-containing peptides in the fetal adrenal medulla. Placental growth was restricted by removal of most of the placental implantation sites in the uterus before mating. In midgestation, placental and fetal body weight were reduced (p < 0.05) in the PR group (n = 8; 237.9 +/- 39.5 g, 564.7 +/- 41.6 g, respectively) when compared with the control group (n = 9; 479.1 +/- 36.9 g, 721.2 +/- 22.8 g, respectively). However, combined fetal adrenal weight and adrenal cortical and medullary area were similar in the PR and control fetuses. In PR fetuses, distribution of staining for dopamine-beta-hydroxylase, phenylethanolamine N-methyltransferase, and ENK-containing peptides in the adrenal medulla was similar when compared with the control group; however, staining was less intense and not all adrenomedullary cells were stained. The total adrenal content of ENK-containing peptides was also significantly (p < 0.05) less in the PR group (103.4 +/- 18.6 ng/adrenal) than in the control group (243.6 +/- 24.8 ng/adrenal). However, the molecular mass profile of ENK-containing peptides was not altered in the PR fetuses compared with controls. These data suggest that placental restriction in utero may alter the synthesis and/or secretion of catecholamines and ENK-containing peptides from the fetal adrenal medulla from as early as 90 d gestation.

D-Ribulose-5-phosphate 3-epimerase: cloning and heterologous expression of the spinach gene, and purification and characterization of the recombinant enzyme

We have achieved, to our knowledge, the first high-level heterologous expression of the gene encoding D-ribulose-5-phosphate 3-epimerase from any source, thereby permitting isolation and characterization of the epimerase as found in photosynthetic organisms. The extremely labile recombinant spinach (Spinacia oleracea L.) enzyme was stabilized by DL-alpha-glycerophosphate or ethanol and destabilized by D-ribulose-5-phosphate or 2-mercaptoethanol. Despite this lability, the unprecedentedly high specific activity of the purified material indicates that the structural integrity of the enzyme is maintained throughout isolation. Ethylenediaminetetraacetate and divalent metal cations did not affect epimerase activity, thereby excluding a requirement for the latter in catalysis. As deduced from the sequence of the cloned spinach gene and the electrophoretic mobility under denaturing conditions of the purified recombinant enzyme, its 25-kD subunit size was about the same as that of the corresponding epimerases of yeast and mammals. However, in contrast to these other species, the recombinant spinach enzyme was octameric rather than dimeric, as assessed by gel filtration and polyacrylamide gel electrophoresis under nondenaturing conditions. Western-blot analyses with antibodies to the purified recombinant enzyme confirmed that the epimerase extracted from spinach leaves is also octameric.

Determination of synapsin I and synaptophysin in body fluids by two-site enzyme-linked immunosorbent assays

Two-site enzyme-linked immunosorbent assays (ELISA) have been established for the specific and sensitive determination of two membrane proteins of the small synaptic vesicles (SSV), namely: peripheral synapsin I and integral synaptophysin. The ELISA used highly specific capture monoclonal antibodies (mAB) and polyclonal antibodies (pAB) as detectors. For synapsin I, the mAB were newly generated, whereas for synaptophysin, the commercially available mAB SY38 was applied. In order to calibrate the ELISA and to raise pAB, both proteins were purified in the mg-range. Synapsin I was purified by conventional means from human and porcine brain and synaptophysin was purified by immunoaffinity chromatography from porcine brain. Using the ELISA, neither synapsin I nor synaptophysin could be determined in serum or cerebrospinal fluid (CSF) from healthy donors or patients suffering various neurological disorders or pheochromocytomas. For this reason, the degradation of both proteins in serum and CSF was investigated. With the exception of synaptophysin measured in serum, both proteins exhibited fast rates of degradation. Despite the negative results in human body fluids, the two ELISA are appropriate for the quantification of these membrane proteins in neuronal or neuroendocrine cell extracts or preparations of SSV.

Glutamate metabolism is down-regulated in astrocytes during experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) was induced in SJL/J mice by adoptive transfer of MBP-reactive T cells in order to investigate the role of astrocytes in pathology. GFAP protein and mRNA expression (analyzed using semiquantitative Western blot and RT-PCR techniques) were upregulated in the spinal cord of mice, which had developed a complete paralysis of hind- and fore-limbs and tail (grade 4 EAE), thus establishing that reactive gliosis occurred under these experimental conditions. Within the same samples and using similar techniques, we found that glutamine synthetase (GS) and glutamate dehydrogenase (GDH) expression were dramatically reduced. These two astrocytic enzymes are responsible for degradation of glutamate, the most abundant excitatory neurotransmitter in the brain. Since elevated levels of glutamate may be neurotoxic, we propose that the decreased capacity of astrocytes to metabolize glutamate may contribute to EAE pathology.

Selective phosphorylation of adult tau isoforms in mature hippocampal neurons exposed to fibrillar A beta

How senile plaques and neurofibrillary tangles are linked represents a major gap in our understanding of the pathophysiology of Alzheimer's disease. We characterized a hippocampal neuronal culture system in which tau undergoes maturation in vivo; rat neurons maintained in culture for more than 3 weeks replicated the splicing and phosphorylation changes that tau undergoes upon maturation in situ. Using this model system, we induced an Alzheimer-like neuritic dystrophy following the application of fibrillar beta-amyloid. The dystrophy consisted of focal distortions and swellings within the neurites and an altered phosphorylation of the adult tau isoforms. Fibrillar beta-amyloid induced the concomitant activation of MAP kinase and GSK3 beta. The aberrant activation of several signaling pathways may lead to the abnormal phosphorylation of tau and neuritic degeneration.

Biochemical and functional characterization of the synaptic vesicle-associated form of CA2+/calmodulin-dependent protein kinase II

Ca+/calmodulin-dependent protein kinase II (CaMPKII) is a brain-enriched protein kinase that plays important roles in synaptic transmission and plasticity. In nerve terminals, a form of CaMPKII is associated with synaptic vesicles and binds the COOH-terminal region of synapsin I (SYNI). The biochemical properties of the vesicle-associated form of CAMPKII have been investigated and compared with those of the soluble forebrain enzyme. Both the alpha- and beta-subunits of CaMPKII copurifying with synaptic vesicles were tightly associated with the vesicle membrane. The vesicle-associated form of CaMPKII was indistinguishable from the soluble form with respect to sites of autophosphorylation, kinetics of both autophosphorylation and SYNI phosphorylation, and induction of autonomous activity upon autophosphorylation. Although both subunits of the soluble CaMPKII interacted with a photoactivatable SYNI derivative, only the alpha-subunit of the synaptic vesicle-associated CaMPKII bound to the COOH-terminal region of SYNI. The latter interaction was strongly dependent on the phosphorylation state of SYNI and on divalent cations, but appeared to be independent of autophosphorylation. These results demonstrate that, although the vesicle-associated form of CaMPKII is catalytically indistinguishable from the soluble form, it exhibits distinct characteristics concerning its association with the vesicle membrane and with SYNI.

Large-scale purification of synaptophysin and quantification with a newly established enzyme-linked immunosorbent assay

Synaptophysin (SYP I), an integral membrane protein, was purified on a large scale (0.55 - 2.7 mg) from isolated small synaptic vesicles (SSV) of porcine cortex. In order to achieve this, a conventional purification procedure which consists of size exlusion chromatography, hydrophobic interaction chromatography and chromatofocusing has been developed. This procedure was compared with purification of SYP I by immunoaffinity chromatography. The elution patterns of both procedures were monitored using sodium dodecylsulfate gel electrophoresis (SDS-PAGE) with subsequent Coomassie blue staining of proteins and simultaneous immunoblotting with SYP I-specific antibody. Contaminating proteins with relative molecular masses (M(r)) very similar to SYP I could be removed during the process of purification, demonstrating that the 38 kDa protein found after Triton X-100 lysis of enriched SSV does not exclusively represent SYP I. A specific antiserum was raised in rabbits using a highly purified preparation of SYP I. This antiserum was used in combination with a monoclonal antibody to establish a specific and sensitive enzyme-linked immunosorbent assay (ELISA) which allowed rapid and reliable quantification of this hydrophobic membrane protein in all purification steps, starting with Triton X-100-lysed brain homogenates. Using this ELISA, the concentration of SYP I in highly purified SSV was determined to be 5.8% of solubilized protein.

Toxin A secretion in Pseudomonas aeruginosa: the role of the first 30 amino acids of the mature toxin

Toxin A, one of several virulence factors secreted by the gram-negative bacterium Pseudomonas aeruginosa, is synthesized as a 71 kDa precursor with a typical prokaryotic leader peptide (LP), and is secreted as a 68 kDa mature protein. Evidence from a previous study suggested that a signal required for toxin A secretion in P. aeruginosa may reside within the region defined by the toxin A LP and the first 30 amino acids (aa) of mature toxin A. In the present study, we have used exonuclease Bal31 deletion analysis to examine the specific role of the first 30 aa in toxin A secretion. Four toxA subclones, which encode products containing the toxin A LP and different segments of the 30-residue region fused to a toxin A carboxy-terminal region, were identified. In addition, a gene fusion encoding a hybrid protein consisting of the LP of P. aeruginosa elastase and the final 305 residues of toxin A, was generated. The cellular location of the toxA subclone products in P. aeruginosa was determined by immunoblotting analysis. Toxin A CRMs (cross-reacting material) encoded by different subclones were detected in different fractions of P. aeruginosa including the periplasm and the supernatant. Results from these studies suggest that (1) mature toxin A contains two separate secretion signals one within the N-terminal region and one within the C-terminal region; and (2) the first 30 residues of the mature toxin A form part of the N-terminal secretion signal.

Topical tretinoin increases the tropoelastin and fibronectin content of photoaged hairless mouse skin

Topical tretinoin treatment of photoaged hairless mice has been shown in previous studies to stimulate formation of a subepidermal zone of new connective tissue characterized by enhanced collagen synthesis. The aims of this study were to localize and/or quantify elastin, fibronectin, and glycosaminoglycans in the same model. Hairless mice (Skh-1) were irradiated thrice weekly for 10 weeks with gradually increasing doses of ultraviolet (up to 4.5 minimal erythema doses per exposure) from Westinghouse FS-40 bulbs. Mice were then treated five times a week with either 0.05% tretinoin, the ethanol:propylene glycol vehicle, or nothing for another 10 weeks. Controls included mice sacrificed after 10 weeks of ultraviolet treatment and age-matched untreated animals. The distribution of elastin and fibronectin was examined by immunofluorescence microscopy, which revealed fine fibrils in the subepidermal zone in tretinoin-treated skin. A quantitative slot-blot immunobinding assay showed that tretinoin induced a threefold higher amount of tropoelastin compared with controls. Insoluble elastin content (desmosine levels) was similar in all groups. Although fibronectin content was increased by ultraviolet radiation, tretinoin treatment induced the largest increase. In contrast, the amount of glycosaminoglycans, although increased by UVB radiation, was reduced by tretinoin treatment.

Band 3 and its peptides during aging, radiation exposure, and Alzheimer's disease: alterations and self-recognition

An aging antigen, senescent cell antigen, resides on the 911 amino acid membrane protein band 3. It marks cells for removal by initiating specific IgG autoantibody binding. Band 3 is a ubiquitous membrane transport protein found in the plasma membrane of diverse cell types and tissues, and in nuclear, mitochondrial, and golgi membranes. Band 3 in tissues such as brain performs the same functions as it does in red blood cells forming senescent cell antigen. Oxidation is a mechanism for generating senescent cell antigen. The aging antigenic sites reside on human band 3 map residues 538-554, and 812-830. Carbohydrate moieties are not required for the antigenicity or recognition of senescent cell antigen. Anion transport site were mapped to residues 588-594, 822-839, and 869-883. The aging vulnerable site which triggers the antigenic site and the transport sites of band 3 were mapped using overlapping synthetic peptides along the molecule. Naturally occurring autoantibodies to regions of band 3 comprising both senescent cell antigen and B cells producing these antibodies were demonstrated in the sera of normal, healthy individuals. The presence of these antibodies tend to increase with age. Individuals with autoimmune diseases (rheumatoid arthritis and systemic lupus erythematosus) have increased antibodies to senescent cell antigen peptides. Radiation exposure results in an increase in antibodies to peptides 588-602 which lies in a transport region containing the aging vulnerable site. Band 3 ages as cells and tissues age. Our studies, to date, indicate, that the anion transport ability of band 3 decreases in brains and lymphocytes from old mice. This decreased transport ability precedes obvious structural changes such as band 3 degradation and generation of SCA, and is the earliest change thus far detected in band 3 function. Other changes include a decreased efficiency of anion transport (decreased Vmax) in spite of an increase in number of anion binding sites (increased Km), decreased glucose transport, increased phosphorylation, increased degradation to smaller fragments as detected by quantitative binding of antibodies to band 3 breakdown products and residue 812-830, and binding of physiologic IgG autoantibodies in situ. The latter 3 findings indicate that post-translational changes occur. In Alzheimer's Disease (AD), our results indicate that post-translational changes occur in band 3. These include decreased band 3 phosphorylation of a 25-28kD segment, increased degradation of band 3, alterations in band 3 recognized by antibodies, and decreased anion and glucose transport by blood cells. Serum autoantibodies were increased in AD patients compared to controls to band 3 peptide 822-839. This band 3 residue lies in an anion transport/binding region.

Activation of p42 mitogen-activated protein kinase by glutamate receptor stimulation in rat primary cortical cultures

Recent studies have identified at least two homologous mitogen-activated protein (MAP) kinases that are activated by phosphorylation of both tyrosine and threonine residues by an activator kinase. To help define the role of these MAP kinases in neuronal signalling, we have used primary cultures derived from fetal rat cortex to assess the regulation of their activity by agonist stimulation of glutamate receptors and by synaptic activity. Regulation was assayed by monitoring changes in both tyrosine phosphorylation on western blots and in vitro kinase activity toward a selective MAP kinase substrate peptide. In initial studies, we found that phorbol ester treatment increased tyrosine phosphorylation of p42 MAP kinase and stimulated MAP kinase activity. A similar response was elicited by three agonists of metabotropic glutamate receptors, i.e., trans-(+/-)-1-amino-1,3-cyclopentane dicarboxylic acid, quisqualate, and (2S,3S,4S)-alpha-(carboxycyclopropyl)glycine. MAP kinase activity and p42 MAP kinase tyrosine phosphorylation were also stimulated by the ionotropic glutamate receptor agonist, kainate, but not by N-methyl-D-aspartate. To examine regulation of MAP kinase by synaptic activity, cultures were treated with picrotoxin, an inhibitor of GABAA receptor-mediated inhibition that enhances spontaneous excitatory synaptic activity. Treatment of cultures with picrotoxin elicited activation of MAP kinase. This response was blocked by tetrodotoxin, which suppresses synaptic activity. These results demonstrate that p42 MAP kinase is activated by glutamate receptor agonist stimulation and by endogenous synaptic activity.

VAT-1 from Torpedo electric organ forms a high-molecular-mass protein complex within the synaptic vesicle membrane

VAT-1 is an abundant 41-kDa protein from Torpedo cholinergic synaptic vesicles. Most of VAT-1 immunoreactivity (70%) is localized to the synaptic vesicle membrane while the rest (30%) copurifies with larger membranous fragments. VAT-1 forms a high-molecular-mass complex within the synaptic vesicle membrane. The Stokes radius of the VAT-1 complex is 4.85 nm and the sedimentation coefficient is 8.0 x 10(-13) S. Using these values, the calculated apparent mass of the VAT-1 complex is 176 kDa and the friction coefficient is consistent with that for a globular protein. Electrophoresis of solubilized synaptic vesicle proteins following cross-linking resulted in a 40-kDa ladder which was detected by VAT-1 antibodies. This is in accord with VAT-1 protein complex being composed primarily of VAT-1 subunits. The hydrodynamic characteristics of the VAT-1 protein complex suggest that it is composed of three or four VAT-1 subunits. Synaptophysin, an abundant component of Torpedo synaptic vesicle membranes, which has a similar apparent size as VAT-1, is not part of the VAT-1 protein complex. Interactions between the subunits within the protein complex do not depend on disulfide bonds or on lowering the ionic strength. However, partial dissociation of VAT-1 subunits from the complex occurs by chelating calcium ions.

Expression study with the Escherichia coli lep gene for leader peptidase in phototrophic purple bacteria

Synthesis and assembly of leader peptidase of Escherichia coli (signal peptidase I), was studied by heterologous expression of its lep gene in three species of phototrophic purple bacteria. Cell extracts of the recipient species showed neither cross reaction with antibodies against E. coli leader peptidase nor cleavage of the model substrate M13-procoat in vitro. The lep gene was transferred via conjugation using the plasmid expression vector for phototrophic bacteria pJAJ9. Plasmid-borne leader peptidase enzyme was identified by immunochemical means. However, extracts of transconjugant cells showed no cleavage function. Trypsin digestion studies revealed that the enzyme was not properly integrated across the host membranes. The data suggest that cleaving enzymes for protein export and/or their assembly pathway in purple bacteria differ from the E. coli type.

Identification of p42 mitogen-activated protein kinase as a tyrosine kinase substrate activated by maximal electroconvulsive shock in hippocampus

Recent studies have demonstrated that administration of an electroconvulsive shock produces a rapid and transient increase in tyrosyl phosphorylation of a approximately 40-kDa protein in rat brain. Initial characterization of this protein's chromatographic properties indicated that it might be a member of a recently identified family of kinases, referred to as mitogen-activated protein (MAP) kinases, that are activated by tyrosyl phosphorylation. In the present study, we have used MAP kinase antisera to assess the identity of this protein. We have found that the approximately 40-kDa phosphotyrosine-containing protein comigrates with p42 MAP kinase (p42mapk) and not with two other 44-kDa MAP kinase family members detected by these antisera. Western blots of proteins immunoprecipitated with MAP kinase antibodies confirm that p42mapk displays increased tyrosyl phosphorylation after an electroconvulsive stimulus. Chromatographic separation of hippocampal extracts indicates that MAP kinase activity elutes in parallel with p42mapk. Accordingly, these studies identify p42mapk as a tyrosyl kinase substrate that is activated by this stimulus and suggest that this form of MAP kinase may be selectively regulated by neuronal stimulation.

Type IV collagen synthesis and accumulation in neonatal rat aortic smooth muscle cell cultures

The production of type IV collagen by cultured neonatal rat aortic smooth muscle cells was monitored over a three-week period to further characterize the extracellular matrix of this unique culture system. Type IV collagen was quantified using a dot immunobinding assay and was found to represent 1% or less of the total collagen produced by these cells in culture. Total collagen represented up to 33% of the total protein. The pattern of type IV collagen production in the media and the cell layer suggests that although these cells synthesize and secrete type IV collagen from the onset of culture, type IV collagen deposition only occurs after the cells have reached confluence. In the presence of ascorbate the amount of type IV collagen peaked in the media in preconfluent cultures. In the absence of ascorbate, little type IV collagen was detected in the media. On the other hand, the presence or absence of ascorbate made little difference in the amount of the total collagen detected in the media, although hydroxylation was affected. Remarkably, in the absence of ascorbate type IV collagen accumulation in the cell layer was similar by the end of the culture period to that in cultures treated with ascorbate. Laminin was not affected by the presence or absence of ascorbate. When these cells were exposed to ascorbate for 24 hours, a peak of soluble elastin was detected in the media. However, soluble elastin was not detected in the media in the absence of ascorbate or in cultures which were maintained in the presence of ascorbate. Modulation of the extracellular matrix with ascorbic acid indicated that type IV collagen deposition did not depend on the presence of ascorbic acid and that there was no discernable interaction between type IV collagen, laminin, and elastin.

Nutritional evaluation of the trypsin (EC 3.4.21.4) inhibitor from cowpea (Vigna unguiculata Walp.)

The effect of feeding rats purified cowpea (Vigna unguiculata Walp.) trypsin (EC 3.4.21.4) inhibitor in a semi-synthetic high-quality diet based on lactalbumin (10 g inhibitor/kg) for 10 d was a moderate reduction in the weight gain of rats in comparison with controls, despite an identical food intake in the two groups. The reduction in the growth rate was about 20% on a live weight basis. However, the corresponding value calculated from the weight of dry carcasses was less, only about 7%, probably because the water content of the body of the two groups of rats was different. Although most of the cowpea trypsin inhibitor (CpTI) was rapidly broken down in the digestive tract, its inclusion in the diet led to a slight, though significant, increase in the nitrogen content of faeces but not of urine. Accordingly, the net protein utilization of rats fed on inhibitor-containing diets was also slightly depressed while their energy expenditure was elevated. In agreement with results obtained for the protease inhibitors of soya bean, the slight anti-nutritional effects of CpTI were probably due mainly to the stimulation of the growth and metabolism of the pancreas. Thus, the nutritional penalty for increased insect-resistance after the transfer of the cowpea trypsin inhibitor gene into food plants is slight in the short-term.

Synaptic vesicle-associated Ca2+/calmodulin-dependent protein kinase II is a binding protein for synapsin I

Synapsin I is a synaptic vesicle-associated phosphoprotein that is involved in the modulation of neurotransmitter release. Ca2+/calmodulin-dependent protein kinase II, which phosphorylates two sites in the carboxy-terminal region of synapsin I, causes synapsin I to dissociate from synaptic vesicles and increases neurotransmitter release. Conversely, the dephosphorylated form of synapsin I, but not the form phosphorylated by Ca2+/calmodulin-dependent protein kinase II, inhibits neurotransmitter release. The amino-terminal region of synapsin I interacts with membrane phospholipids, whereas the C-terminal region binds to a protein component of synaptic vesicles. Here we demonstrate that the binding of the C-terminal region of synapsin I involves the regulatory domain of a synaptic vesicle-associated form of Ca2+/calmodulin-dependent protein kinase II. Our results indicate that this form of the kinase functions both as a binding protein for synapsin I, and as an enzyme that phosphorylates synapsin I and promotes its dissociation from the vesicles.

Immunogenic potential of Aspergillus nidulans subcellular fractions and their polypeptide components

Cell-free extracts of the ascomycetous fungus Aspergillus nidulans were separated into three subcellular fractions: cell walls, total membranes and cytosol, and two different immunization protocols were used to raise antibodies against them in 12 New Zealand rabbits. The immune response was followed over time by dot and Western blot analyses to determine the immunogenic potential of each individual fraction and their polypeptide components. The IgG fractions, purified from pools of the best sera, were used to analyze in detail the antigenic composition of A. nidulans mycelium. The fast immunization protocol provided a much earlier response and higher sera titres. Cytosols and membranes were more immunogenic than cell walls and, in most cases, a positive correlation was shown between the titre of each serum and the number of detected antigens. The polypeptides of A. nidulans included six major immunodominant antigens of the molecular weights ranging between 13 and 200 kDa.

Suppression of kinesin expression in cultured hippocampal neurons using antisense oligonucleotides

Kinesin, a microtubule-based force-generating molecule, is thought to translocate organelles along microtubules. To examine the function of kinesin in neurons, we sought to suppress kinesin heavy chain (KHC) expression in cultured hippocampal neurons using antisense oligonucleotides and study the phenotype of these KHC "null" cells. Two different antisense oligonucleotides complementary to the KHC sequence reduced the protein levels of the heavy chain by greater than 95% within 24 h after application and produced identical phenotypes. After inhibition of KHC expression for 24 or 48 h, neurons extended an array of neurites often with one neurite longer than the others; however, the length of all these neurites was significantly reduced. Inhibition of KHC expression also altered the distribution of GAP-43 and synapsin I, two proteins thought to be transported in association with membranous organelles. These proteins, which are normally localized at the tips of growing neurites, were confined to the cell body in antisense-treated cells. Treatment of the cells with the corresponding sense oligonucleotides affected neither the distribution of GAP-43 and synapsin I, nor the length of neurites. A full recovery of neurite length occurred after removal of the antisense oligonucleotides from the medium. These data indicate that KHC plays a role in the anterograde translocation of vesicles containing GAP-43 and synapsin I. A deficiency in vesicle delivery may also explain the inhibition of neurite outgrowth. Despite the inhibition of KHC and the failure of GAP-43 and synapsin I to move out of the cell body, hippocampal neurons can extend processes and acquire as asymmetric morphology.

Soybean protein isolate and soybean lectin inhibit iron absorption in rats

Inhibitory effects of soybean protein isolate (SPI) and soybean lectin on the intestinal absorption of nonheme iron were investigated by in vivo studies in rats. Rats fed the SPI-based diet absorbed significantly less iron than did control rats fed the casein-based diet. Supplementing the SPI diets with 8% D-galactose significantly increased the incorporation of iron into liver ferritin, although D-galactose did not significantly increase iron absorption. Heat treatment of SPI significantly increased iron absorption. Ascorbate did not enhance iron absorption in rats fed the SPI-based diet. The presence of lectin in an aqueous extract of SPI was suggested by hemagglutination activity as well as by immunoreactivity with soybean lectin antibody. Soybean lectin introduced into ligated segments of the upper small intestine of rats inhibited ferrous iron absorption. This inhibitory effect, especially in the mucosal uptake, was significantly improved by addition of N-acetyl-D-galactosamine to soybean lectin. Soybean lectin had no effect on ferric iron absorption. Our results suggest that a portion of the reduction in iron absorption in rats fed SPI may be due to lectins.

Structure-function analysis of exotoxin A proteins with mutations at histidine 426

Substitution of Tyr for His-426 of Pseudomonas aeruginosa exotoxin A results in a mutant protein with reduced ADP-ribosyltransferase activity (M. J. Wick and B. H. Iglewski, J. Bacteriol. 170:5385-5388, 1988). To investigate the role of His-426 in enzymatic activity, oligonucleotide-directed mutagenesis was used to construct mutant proteins encoding Ala, Glu, Gly, Lys, or Pro at position 426. The effect of these amino acid substitutions on ADP-ribosyltransferase activity was analyzed in 34,000-Da carboxy-terminal exotoxin A peptides (H426n peptides). ADP-ribosyltransferase activity of the H426n peptides fell within a range between 0.002 and 28% of wild-type levels of activity, suggesting that His-426 is required for full expression of enzymatic activity of exotoxin A. To investigate a possible catalytic function of His-426, the abilities of full-size (66,000-Da) wild-type exotoxin A and mutant proteins encoding either Ala-426 or Tyr-426 to hydrolyze NAD were compared by measuring NAD-glycohydrolase activity. This analysis revealed that exotoxin A encoding either Ala-426 or Tyr-426 expressed less than 1% of wild-type levels of NAD-glycohydrolase activity. Several criteria, including differential enzymatic activation properties and unique tryptic digestion patterns, revealed that the wild-type and mutant full-size proteins exhibit conformational differences. Our data suggest that His-426 plays a critical structural role in establishing the molecular architecture of the catalytic site in domain III and is important in orienting active-site residues in the cleft.

Cellular immune crossreactivity between myelin basic protein and synapsin in rats with experimental allergic encephalomyelitis

We previously demonstrated that antibodies against myelin basic protein (MBP) obtained from animals with experimental allergic encephalomyelitis (EAE), induced with MBP and purified by affinity chromatography, have the property to recognize a neuronal protein, synapsin Ia and Ib. To investigate whether this crossreactivity also occurs at the cellular level, we purified spleen and lymph node mononuclear cells from rats sensitized with MBP or synapsin using polystyrene plates coated with the respective antigen. We observed that animals injected with MBP have T lymphocytes that bind both antigens. Using the same system, each purified cell population was confronted again to the studied antigens. The anti-MBP cells recognized once more epitopes of MBP and about 40% of them also recognized synapsin. On the other hand, cells that first were attached to synapsin, in the second exposure to antigens bound to MBP and synapsin in similar amounts. Double immunofluorescent labeling of the mononuclear cells isolated from animals injected with bovine myelin or MBP showed that the same lymphocyte was able to recognize MBP as well as synapsin. In both experimental systems the quantitative results were similar indicating that in bovine myelin- or MBP-sensitized animals practically all the cells that recognize synapsin are anti-MBP cells, and of the total cells raised against MBP, around 40% of them show this crossreactivity. On the contrary, animals injected with synapsin have cells that bind to this protein but not to MBP indicating that the described crossreactivity, as observed at humoral level, is only in one way.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of mature tau isoforms in the stabilization of neurites in PC12 cells

Tau microtubule-associated proteins are believed to play a role in regulation of the growth of neuronal processes. In order to study the function of tau protein in vivo, we examined the inhibition of tau expression in PC12 cells by exposing the cells to tau antisense oligodeoxynucleotides. A specific retraction of neurites was observed after 3-4 days of incubation with nerve growth factor (NGF) and the antisense oligodeoxynucleotides. This is different from the previously described retraction of neurites at the initiation step following exposure to tubulin antisense oligodeoxynucleotides, indicating that tau proteins are involved at later stages of neurite outgrowth. Analysis of tau protein isoforms in NGF-induced PC12 cells showed a transition from immature to mature tau isoforms, thus relating the appearance of the latter with the stabilization step of neurite outgrowth. Use of an RNase-protection assay demonstrated a similar switch from immature to mature tau mRNA species. The transition to stable microtubules was verified by the appearance of microtubule bundles and their stability to colchicine treatment. Both phenomena occurred between 2 and 4 days of NGF induction. These results indicate that in vivo only mature tau isoforms are involved in the transition from unstable to stable neurites, which is a key step in neuronal development.