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PubMedDate not supplied

Protein III, a neuron-specific phosphoprotein: variant forms found in human brain.

Protein III is a neuron-specific phosphoprotein which consists of two polypeptides, IIIa (Mr 74 kD) and IIIb (Mr 55 kD). This phosphoprotein has previously been shown to be associated with synaptic vesicles. In the present investigation, we have examined Protein III in human brain tissue. In contrast to observations in rat brain, where only one form of Protein IIIb (Mr 55 kD) has been found, in human brain tissue three variants of Protein IIIb, designated Protein IIIb1 (Mr 55 kD), Protein IIIb2 (Mr 57 kD) and Protein IIIb3 (Mr 59 kD), were observed by both biochemical and immunochemical assays. Protein IIIa from human brain also exhibited three variants in electrophoretic mobility. Peptide maps of Proteins IIIa and IIIb revealed that the differences in electrophoretic mobility of the variants of these proteins were preserved in variants (Mr 18kD, Mr20kD, and Mr22kD) of a smaller peptide fragment. These variant forms of Protein III were studied in brains from individuals without any history of neurological or psychiatric illness, as well as from individuals who had suffered from one of several types of neuropathological conditions, such as chronic alcoholism, Alzheimer's disease, multi-infarct dementia, and Parkinson's disease. Some differences were observed in the distribution of variants among the various clinical categories.

Adult↗
PubMed1981

Affinity-purified anti-protein I antibody. Specific inhibitor of phosphorylation of protein I, a synaptic protein.

Protein I is a synaptic protein which serves as an endogenous substrate for cyclic AMP- and calcium-dependent protein kinases. Antibodies raised against purified Protein I have been isolated from rabbit antiserum by affinity chromatography on Protein I-conjugated agarose column. The purified antibodies were identified as immunoglobulin G by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Ouchterlony double immunodiffusion precipitation test. The purified antibodies not only inhibited the phosphorylation of purified Protein I by exogenous cyclic AMP-dependent protein kinase, but also inhibited specifically the phosphorylation of Protein I by endogenous cyclic AMP-dependent protein kinase in a synaptic vesicle fraction, synaptic junctional complex fraction, synaptic membrane fraction, and crude homogenate of cerebrum. The purified anti-Protein I antibodies also inhibited with a similar potency calcium-dependent phosphorylation of Protein I without affecting the phosphorylation of other proteins. The Fab(t) fragment of anti-Protein I immunoglobulin G, which was produced by tryptic digestion, retained the ability to inhibit specifically the phosphorylation of Protein I. This substrate-directed, specific inhibitor of the phosphorylation of Protein I may provide a unique probe for investigating the function of Protein I phosphorylation.

Animals↗
PubMed1982

Distribution of protein I and regulation of its state of phosphorylation in the rabbit superior cervical ganglion.

The distribution and regulation of the state of phosphorylation of Protein I have been studied in the rabbit superior cervical sympathetic ganglion. The data indicate that the ganglion contains two pools of Protein I: a presynaptic pool that represents 60% of the total ganglion Protein I and a postsynaptic pool that represents 40% of the total ganglion Protein I. The state of phosphorylation of presynaptic Protein I, but not that of postsynaptic Protein I, is regulated by nerve impulse conduction, by dopamine, and by a high K+ concentration. Studies of the extracellular calcium requirements for Protein I phosphorylation, as well as peptide-mapping analyses of Protein I, suggest that the effects of nerve impulse conduction and of a high K+ concentration are mediated through the activation of calcium-dependent protein kinases and that the effect of dopamine is mediated through the activation of cyclic AMP-dependent protein kinase. The total amount of postsynaptic Protein I, but not that of presynaptic Protein I, is decreased by short periods of exposure to cycloheximide, a protein synthesis inhibitor. It is proposed that Protein I located in presynaptic nerve terminals plays a functional role in those terminals and that the Protein I located in cell bodies is newly synthesized and en route to nerve terminals.

Animals↗
PubMedDate not supplied

[The synaptic proteins of the temporal associative area in the neocortex (field Ep) of cats with normal and decreased cognitive capacities].

Fractions of light and heavy synaptosomes were prepared from associative temporal area of cat brain, which were previously tested behaviorally for ability to solve the generalization, gnostic and abstraction tasks. The synaptic membrane subfractions and synaptoplasma fractions were isolated and the content of the total protein and of the demasked protein sulfhydryl groups (SH groups) was investigated spectrophotometrically. The maximal content of the demasked SH groups was revealed in the upper subfractions (mainly the membranes of cholinergic synapses) and minimal content--in the lower subfractions (mainly noncholinergic synapses). Significantly smaller total protein content in the upper and middle subfractions of light synaptosomes was found, and more demasked SH groups in the membrane-bound proteins of the upper and middle subfractions of light and heavy synaptosomes was found in the cortex area of the "clever" then "silly" cats. Suggestion concerning characteristic for brains of "clever" cats relatively low total quantity of synapses in the area Ep of the cortex and significantly higher proportion of cholinergic ones is discussed.

Animals↗
PubMed1998

Neurotrophins induce formation of functional excitatory and inhibitory synapses between cultured hippocampal neurons.

Cell cultures were used to analyze the role of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in the development of synaptic transmission. Neurons obtained from embryonic day 18 (E18) rat hippocampus and cultured for 2 weeks exhibited extensive spontaneous synaptic activity. By comparison, neurons obtained from E16 hippocampus expressed very low levels of spontaneous or evoked synaptic activity. Neurotrophin treatment produced a sevenfold increase in the number of functional synaptic connections in the E16 cultures. BDNF induced formation of both excitatory and inhibitory synapses, whereas NT-3 induced formation of only excitatory synapses. These effects were independent of serum or the age of the glia bed used for the culture. They were not accompanied by significant changes in synaptic-vesicle-associated proteins or glutamate receptors. Treatment of the cultures with the neurotrophins for 3 d was sufficient to establish the maximal level of functional synapses. During this period, neurotrophins did not affect the viability or the morphology of the excitatory neurons, although they did produce an increase in the number and length of dendrites of the GABAergic neurons. Remarkably, only BDNF caused an increase in the number of axonal branches and in the total length of the axons of the GABAergic neurons. These results support a unique and differential role for neurotrophins in the formation of excitatory and inhibitory synapses in the developing hippocampus.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1999

The sec6/8 complex is located at neurite outgrowth and axonal synapse-assembly domains.

The molecules that specify domains on the neuronal plasma membrane for the delivery and accumulation of vesicles during neurite outgrowth and synapse formation are unknown. We investigated the role of the sec6/8 complex, a set of proteins that specifies vesicle targeting sites in yeast and epithelial cells, in neuronal membrane trafficking. This complex was found in layers of developing rat brain undergoing synaptogenesis. In cultured hippocampal neurons, the sec6/8 complex was present in regions of ongoing membrane addition: the tips of growing neurites, filopodia, and growth cones. In young axons, the sec6/8 complex was also confined to periodic domains of the plasma membrane. The distribution of synaptotagmin, synapsin1, sec6, and FM1-43 labeling in cultured neurons suggested that the plasma membrane localization of the sec6/8 complex preceded the arrival of synaptic markers and was downregulated in mature synapses. We propose that the sec6/8 complex specifies sites for targeting vesicles at domains of neurite outgrowth and potential active zones during synaptogenesis.

Animals↗