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M Popoli

Publications and source records attributed to M Popoli.

9 recordsLinked to original sources
PubMed1992

Isolated p65 protein reproduces membrane binding activity of synaptic vesicles.

Purified synaptic vesicles are highly enriched with a protein which binds cell plasma membranes. The binding is selective for acidic phospholipids and sialoglycosphingolipids. In partition chromatography of vesicle proteins, the binding activity was co-eluted with a limited set of proteins. Among them the most abundant species were two vesicle-specific proteins: p65 and synaptophysin. In affinity chromatography of vesicle proteins, only p65 bound to a column of immobilized lysoganglioside. The same protein, purified by preparative electrophoresis, retained the binding activity and fully reproduced the hemagglutinating property and the selectivity for acidic lipids of whole vesicles. The results suggest that the (hemagglutinating) lipid binding properties of the vesicles are mainly if not exclusively due to p65.

Calcium-Binding Proteins↗
PubMed1991

Properties of a synaptic vesicle protein binding plasma membranes.

Synaptic vesicles contain a protein (agglutinin) which binds cell plasma membranes. The protein activity is titrated measuring the agglutination of rabbit trypsinized-fixed red blood cells induced by serial dilutions of purified vesicles. The protein is highly concentrated in vesicles: the specific activity is 150-fold higher in vesicles compared to the brain homogenate, and 20-fold higher compared to the crude synaptosomal membrane fraction. The binding is specifically inhibited by the four major brain sialoglycosphingolipids, with a higher affinity for polysialo- rather than for monosialoganglioside (GM1) IC50 are 3.9 x 10(-5) M (GT1b), 8.9 x 10(-5) M (GD1a), 2.8 x 10(-4) M (GD1b) and 4.9 x 10(-4) M (GM1). Cells which are not agglutinated by the vesicles (human red blood cells) can be activated by incubation with gangliosides: insertion of the glycolipids in the plasma membranes makes them sensitive to the vesicle haemagglutinin.

Animals↗
PubMed1988

A hemagglutinin specific for sialic acids in a rat brain synaptic vesicle-enriched fraction.

A hemagglutinating activity was detected in a synaptic vesicle-enriched fraction prepared from adult rat brain, using trypsinized glutaraldehyde-fixed rabbit erythrocytes. The specific activity of the fraction, in two series of experiments, was 7.5 and 16-fold higher than in the other subcellular fractions. The activity was absent from the synaptosome cytosol. In a study using twenty-five different carbohydrates and glycoproteins, best inhibitors were N-acetylneuraminic acid and N-glycolylneuraminic acid, together with bovine submaxillary mucin and a glycopeptide fraction prepared from rabbit erythrocyte membranes. The activity was thermolabile and very sensitive to proteolytic enzymes (but insensitive to neuraminidase) indicating that a protein (agglutinin) is responsible for the activity. Experiments using detergents and high ionic strength showed that the agglutinin is tightly bound to membranes, inactivated by the so-called non denaturing detergents, and stable in diluted sodium dodecyl sulphate. Hypotheses are discussed on the possible function of the agglutinin.

Animals↗
PubMed1988

Spermine binding to subsynaptosomal fractions of rat brain cortex.

Binding sites for [14C]spermine have been identified in rat brain cortex subcellular fractions. The binding, characterized by using synaptosomal membranes, is specific for spermine. It was not detected below 20 degrees C and increased about three/four-fold with a temperature rise of 10 degrees C. Binding occurred only in the presence of -SH reducing agents. It was completely suppressed by metal chelating agents, and was stimulated about four-fold by 1-5 x 10(-5) M Fe2+. Smaller increases were observed in the presence of Mn2+, Ni2+, Ca2+, Mg2+, and Zn2+; in contrast, millimolar concentrations of most divalent cations inhibited the binding differently (Mn2+ = Ni2+ = Zn2+ = Co2+ much greater than Mg2+ greater than Ca2+). Bound radioactive spermine was not displaced by the addition of high concentrations of unlabelled polyamine or chelating agents, nor by precipitation and washing of the membranes with 10 percent trichloroacetic acid, or by boiling of the precipitate in the presence of 1.0 percent SDS and 10 percent beta-mercaptoethanol. The trichloroacetic acid precipitate showed two radioactive bands, corresponding to low Mr (less than 8,000) components, after SDS-polyacrylamide gel electrophoresis and fluorography. The Fe2+-stimulated [14C]spermine binding was neither influenced by a previous heating of the membranes at 100 degrees C for 30 min nor by trypsin or pronase digestion, whereas the heat-treatment increased the binding occurring in the absence of Fe2+ by about two fold. A non-enzymatic formation of a spermine-metal complex tightly bound to some membrane peptide(s) is suggested.

Animals↗
PubMed1986

Protein organization of rat synaptic plasma membranes and synaptic vesicles: a one- and two-dimensional study.

The protein organization of rat brain synaptic plasma membranes (SPM) and synaptic vesicles (SV) was investigated by surface iodination and one- and two-dimensional electrophoresis. Polypeptides of molecular weights (MWs, in Kilodaltons) 170 K, 135 K, 96-86 K, 68-64-61 K, 56 K, 52 K, 38 K, 35-33 K, and 18 K are predominantly or exclusively exposed on the extracellular side of synaptosomes. Several polypeptides of MW between 70 K and 40 K are exclusively exposed on the cytoplasmic side of SPM. The use of two-dimensional electrophoresis allowed to recognize that, for some classes of MW, there are polypeptides of nearly the same MW and different isoelectric points exposed on both sides of SPM. The synaptosomal membrane shows a predominance of acidic proteins on the extracellular side and more neutral and basic proteins on the cytoplasmic side. With respect to SPM, SV are particularly enriched with polypeptides of MW 71 K, 56 K, 39-38 K, 32 K, 16 K, and 15 K. One of them, a doublet of MW 39-38 K, is the most highly labeled species upon surface iodination and is similar, but not identical, with a doublet located on the cytoplasmic side of SPM.

Animals↗