Actin and tubulin binding domains of synapsins Ia and Ib

Synapsins Ia and Ib are neuronal phosphoproteins involved with the regulated clustering of small synaptic vesicles at the presynaptic terminus. In vitro they bind and bundle filaments of both actin and tubulin. Previously, we identified an actin binding domain in the NH2-terminal 25-kDa fragment (N25) generated by 2-nitro-5-thiocyanobenzoic acid (NTCB) cleavage of synapsin I and found that a complementary COOH-terminal 52-kDa portion of the molecule (N52) contained either a second actin binding site or a site of self-association [Petrucci, T. P., & Morrow, J. S. (1987) J. Cell. Biol. 105, 1355]. Using direct binding assays between actin, tubulin, and specific synapsin NTCB-derived peptides, we confirm the ability of purified N25 to bind but not bundle actin and demonstrate that the complementary N52 (or N50) fragments from synapsins Ia and Ib and a 14-kDa fragment derived from the middle of the molecule also associate directly with actin. An antibody specific for N25 inhibits the actin binding activity of N25 and the actin bundling but not the actin binding activity of intact synapsin I. Similar studies conducted with purified tubulin and tubulin immobilized on Sepharose demonstrate that both tubulin and actin bind at approximately the same sites in the NH2-terminal half of synapsin I. Although the fragments derived from the COOH terminus of both synapsin Ia and synapsin Ib (N40b/N34) were devoid of measurable actin binding activity after NTCB cleavage, they were specifically labeled in the intact molecule by a photoactivated cross-linker bound to F-actin. Collectively, these results indicate that synapsins Ia and Ib possess two actin and tubulin binding domains located in the NH2-terminal half of the molecule and suggest that a third actin binding domain is located in the COOH-terminal region. The NH2-terminal sites are found in NTCB peptides N25 and N14, while the third site, apparently of lower affinity, resides in N40b/N34. It is hypothesized that, in the intact molecule, the two NH2-terminal domains contribute to a single high-affinity actin and/or tubulin binding site in the "globular" head region of synapsin I, while the third actin binding domain constitutes the topographically distinct site required for the actin bundling activity of the native molecule. The 45-residue COOH extension that distinguishes synapsin Ia from synapsin Ib appears not to be involved with actin binding, since no differences were found in the ability of N40b and N34 to be photo-cross-linked to actin.(ABSTRACT TRUNCATED AT 400 WORDS)     

Tyrosine phosphorylation of beta-dystroglycan at its WW domain binding motif, PPxY, recruits SH2 domain containing proteins.

beta-Dystroglycan is a ubiquitously expressed integral membrane protein that undergoes tyrosine phosphorylation in an adhesion-dependent manner. However, it remains unknown whether tyrosine-phosphorylated beta-dystroglycan interacts with SH2 domain containing proteins. Here, we show that the tyrosine phosphorylation of beta-dystroglycan is constitutively elevated in v-Src transformed cells. We next reconstituted this phosphorylation event in vivo by transiently coexpressing wild-type c-Src with a fusion protein containing full-length beta-dystroglycan. Our results demonstrate that Src-induced tyrosine phosphorylation of beta-dystroglycan is strictly dependent on the presence of a PPxY motif at its extreme C-terminus. In the nonphosphorylated state, this PPxY motif is normally recognized as a ligand by the WW domain; phosphorylation at this site blocks the binding of certain WW domain containing proteins. Using a GST fusion protein carrying the cytoplasmic tail of beta-dystroglycan, we identified five SH2 domain containing proteins that interact with beta-dystroglycan in a phosphorylation-dependent manner, including c-Src, Fyn, Csk, NCK, and SHC. We localized this binding activity to the PPxY motif by employing a panel of beta-dystroglycan-derived phosphopeptides. In addition, tyrosine phosphorylation of beta-dystroglycan in vivo resulted in the coimmunoprecipitation of the same SH2 domain containing proteins, and this binding event required the beta-dystroglycan C-terminal PPxY motif. We discuss the possibility that tyrosine phosphorylation of the PPxY motif within beta-dystroglycan may act as a regulatory switch to inhibit the binding of certain WW domain containing proteins, while recruiting SH2 domain containing proteins.     

Guaiphenesin-ketamine-xylazine infusion to maintain anesthesia in mules undergoing field castration

Background

In order to determine whether a combination of guaiphenesin, ketamine and xylazine can induce safe and satisfactory anaesthesia in mules undergoing field castration, eight healthy adult intact male mules were employed. They were premedicated with intravenous (IV) xylazine (1.3 mg/kg); an additional dose of xylazine (0.3 mg/kg IV) was administered in case of inadequate depth of sedation. Anaesthesia was induced with IV thiopental (6 mg/kg). The quality of sedation and induction was recorded. Anaesthesia was maintained with an infusion of guaiphenesin (50 mg/mL), ketamine (2 mg/mL) and xylazine (1 mg/mL) (GKX). The spermatic cord of each testis was infiltrated with 5 mL of 2% lidocaine. During anaesthesia heart rate (HR), respiratory rate (RR), rectal temperature (RT) and haemoglobin oxygen saturation (SpO₂) were measured every 5 min. The data were analysed with simple one-way analysis of variance (ANOVA). A P value < 0.05 was considered statistically significant. Time of anesthesia, time of surgery and time of recovery were recorded.

Results

Only one mule required an additional dose of xylazine to achieve a satisfactory depth of sedation. Thiopental at the dose of 6 mg/kg IV resulted in smooth induction and lateral recumbency in all animals. GKX provided adequate anaesthesia to perform castration in all mules. Muscle relaxation was deemed adequate and physiological variables remained stable and within references values during the anaesthesia and did not change in response to surgical stimulation. Time (mean ± standard deviation) from the end of the infusion to sternal recumbency and time from sternal recumbency to standing were 27.7 ± 4.6 and 30.1 ± 7.7 min, respectively.

Conclusions

The combination of xylazine, thiopental and GKX provides satisfactory short-term anaesthesia in mules undergoing field castration.

     

Peroxynitrite affects exocytosis and SNARE complex formation and induces tyrosine nitration of synaptic proteins

The reactive species peroxynitrite, formed via the near diffusion-limited reaction of nitric oxide and superoxide anion, is a potent oxidant that contributes to tissue damage in neurodegenerative disorders. Peroxynitrite readily nitrates tyrosine residues in proteins, producing a permanent modification that can be immunologically detected. We have previously demonstrated that in the nerve terminal, nitrotyrosine immunoreactivity is primarily associated with synaptophysin. Here we identify two other presynaptic proteins nitrated by peroxynitrite, Munc-18 and SNAP25, both of which are involved in sequential steps leading to vesicle exocytosis. To investigate whether peroxynitrite affects vesicle exocytosis, we used the fluorescent dye FM1-43 to label a recycling population of secretory vesicles within the synaptosomes. Bolus addition of peroxynitrite stimulated exocytosis and glutamate release. Notably, these effects were strongly reduced in the presence of NaHCO(3), indicating that peroxynitrite acts mainly intracellularly. Furthermore, peroxynitrite enhanced the formation of the sodium dodecyl sulfate-resistant SNARE complex in a dose-dependent manner (100-1000 microm) and induced the formation of 3-nitrotyrosine in proteins of SNARE complex. These data suggest that modification(s) of synaptic vesicle proteins induced by peroxynitrite may affect protein-protein interactions in the docking/fusion steps, thus promoting exocytosis, and that, under excessive production of superoxide and nitric oxide, neurons may up-regulate neuronal signaling.     

Evaluation of the antioxidant activity of flavonoids by "ferric reducing antioxidant power" assay and cyclic voltammetry

Flavonoids, naturally occurring phenolic compounds, have recently been studied extensively for their antioxidant properties. The structure-antioxidant activity relationships (SAR) of flavonoids have been evaluated against different free radicals, but "ferric reducing antioxidant power" (FRAP) assay, which determines directly the reducing capacity of a compound, has not been used for this purpose. In this study, the antioxidant activities of 18 structurally different flavonoids were evaluated by FRAP assay modified to be used in 96-well microplates. Furthermore, their oxidation potentials were also measured, which were in the range of +0.3 V (myricetin) to +1.2 V (5-hydroxy flavone) and were in good agreement with FRAP assay results. Quercetin, fisetin and myricetin had the lowest oxidation potentials and appeared the most active compounds in FRAP assay and were 3.02, 2.52 and 2.28 times more active than Trolox, respectively. Indications were found that the o-dihydroxy structure in the B ring and the 3-hydroxy group and 2,3-double bond in the C ring give the highest contribution to the antioxidant activity.     

Immunodetection of partially glycosylated isoforms of alpha-dystroglycan by a new monoclonal antibody against its beta-dystroglycan-binding epitope

The alpha/beta dystroglycan (DG) complex links the extracellular matrix to the actin cytoskeleton. The extensive glycosylation of alpha-DG is believed to be crucial for the interaction with its extracellular matrix-binding partners. We characterized a monoclonal antibody, directed against the beta-DG-binding epitope ( approximately positions 550-565), which recognizes preferentially hypoglycosylated alpha-DG. In Western blot, the antibody was able to detect a number of partially glycosylated alpha-DG isoforms from rat brain and chicken skeletal muscle tissue samples. In addition, we demonstrated its inhibitory effect on the interaction between alpha- and beta-DG in vitro and preliminary immunostaining experiments suggest that such hypoglycosylated alpha-DG isoforms could play a role within cells.     

L’industrie lithique du site Pléistocène inférieur de Pirro Nord (Apricena, Italie du sud) : une occupation humaine entre 1,3 et 1,7 Ma

The site of Pirro Nord (also known as Cava Pirro or Cava Dell’Erba) is known in literature since the 1970's of the last century as a palaeontological site, of which the mammalian fossil association constitutes a reference (local) fauna for the European latest Villafranchian. This fossil association is also known for the occurrence of some African elements. During the 2005, a lithic industry has been found in three karst fissures, together with the typical elements of the Pirro Nord vertebrate assemblage. The biochronological assessment based on the vertebrate assemblage attributes it to a time interval bracketed between 1.3 Ma and 1.7 Ma. Thus the site of Pirro Nord represents the oldest human occupation of Europe so far known. The lithic assemblage, attributable to the Mode 1, is constituted by three cores and seven flakes, and is made only on flint. Lithic artefacts have been found in stratigraphic context during the preliminary surveys of the three fissures, that they will be the object of systematic excavations in the years to come.