Proteome Analysis of PC12 Cells Reveals Alterations in Translation Regulation and Actin Signaling Induced by Clozapine

Neurochemical Research - Although antipsychotics are routinely used in the treatment of schizophrenia for the last decades, their precise mechanism of action is still unclear. In this study, we...     

Diffusion coefficient of fluorescent phosphatidylinositol 4,5-bisphosphate in the plasma membrane of cells

Phosphatidylinositol 4,5-bisphosphate (PIP₂) controls a surprisingly large number of processes in cells. Thus, many investigators have suggested that there might be different pools of PIP₂ on the inner leaflet of the plasma membrane. If a significant fraction of PIP₂ is bound electrostatically to unstructured clusters of basic residues on membrane proteins, the PIP₂ diffusion constant, D, should be reduced. We microinjected micelles of Bodipy TMR-PIP₂ into cells, and we measured D on the inner leaflet of fibroblasts and epithelial cells by using fluorescence correlation spectroscopy. The average ± SD value from all cell types was D = 0.8 ± 0.2 μm²/s (n = 218; 25°C). This is threefold lower than the D in blebs formed on Rat1 cells, D = 2.5 ± 0.8 μm²/s (n = 26). It is also significantly lower than the D in the outer leaflet or in giant unilamellar vesicles and the diffusion coefficient for other lipids on the inner leaflet of these cell membranes. The simplest interpretation is that approximately two thirds of the PIP₂ on inner leaflet of these plasma membranes is bound reversibly.     

The Effect of Acute Hypoxia on Synaptosomes from Rat Brain

Abstract: Synaptosomes have been isolated from the brains of nonanesthetized and nembutal-anesthetized rats subjected to 30 min hypoxia induced by breathing 7% oxygen in nitrogen. The respiratory rate was depressed in synaptosomes from starved hypoxic animals but was not significantly different from the respective control values in preparations from fed hypoxic animals, anesthetized animals, and hypoxic nonanesthetized animals allowed to recover from the hypoxic episode by 60 min of normoxic conditions. Observations are also reported concerning the levels of various metabolites in the synaptosomes isolated from the brains of the same groups of animals. It is suggested that hypoxia results in damage to the synaptosomal and/or mitochondrial membrane, which modifies substrate oxidation in the mitochondria and decreases availability of reducing equivalents for the respiratory chain. Results obtained on afflicted and recovered animals indicate that synaptosomal preparations provide a useful model for the study of hypoxic damage.     

Expression of soluble recombinant TGF-beta type II receptor fused with the Fc portion of human IgG1 (sTbetaRII-Fc) in NS0 cells

We have constructed and expressed recombinant chimeric soluble TGF-beta type II receptor fused with the Fc portion of human IgG1 (sTbetaRII-Fc) in NS0 mouse myeloma cells and isolated cell lines constitutively secreting very high levels of biologically active protein. The GS-NS0 expression system takes advantage of the strong human cytomegalovirus immediate early promoter expression vector and glutamine synthetase as a selectable marker. The recombinant chimeric receptor could be produced in high amounts and efficiently purified by one step chromatography on a protein A column. Biochemical studies revealed that recombinant sTbetaRII-Fc binds native TGF-beta1 and TGF-beta3 isoforms and neutralizes their activity in vitro.     

The binding of the PDZ tandem of syntenin to target proteins

PDZ domains are among the most abundant protein modules in the known genomes. Their main function is to provide scaffolds for membrane-associated protein complexes by binding to the cytosolic, C-terminal fragments of receptors, channels, and other integral membrane proteins. Here, using both heteronuclear NMR and single crystal X-ray diffraction, we show how peptides with different sequences, including those corresponding to the C-termini of syndecan, neurexin, and ephrin B, can simultaneously bind to both PDZ domains of the scaffolding protein syntenin. The PDZ2 domain binds these peptides in the canonical fashion, and an induced fit mechanism allows for the accommodation of a range of side chains in the P(0) and P(-)(2) positions. However, binding to the PDZ1 domain requires that the target peptide assume a noncanonical conformation. These data help explain how syntenin, and perhaps other PDZ-containing proteins, may preferentially bind to dimeric and clustered targets, and provide a mechanistic explanation for the previously reported cooperative ligand binding by syntenin's two PDZ domains.     

Ca2+-independent binding and cellular expression profiles question a significant role of calmyrin in transduction of Ca2+-signals to Alzheimer's disease-related presenilin 2 in forebrain

The interaction between the EF-hand Ca(2+)-binding protein calmyrin and presenilin 2 (PS2) has been suggested to play a role in Alzheimer's disease (AD). We now report that calmyrin binds specifically endogenous PS2 and not PS1. However, binding appears to be Ca(2+)-independent and calmyrin does not exhibit a Ca(2+)-dependent translocation to intracellular membranes as demonstrated in a Ca(2+)-myristoyl switch assay. Moreover, calmyrin is only present at very low levels in brain areas associated with the onset of AD. In rat, forebrain calmyrin is localized only in a subset of principal neurons, similarly as in human forebrain. Finally, subcellular fractionation demonstrates only a limited overlap of calmyrin and PS2 at neuronal membranes. We therefore conclude that calmyrin will not contribute significantly as a Ca(2+)-sensor that transduces Ca(2+)-signaling events to PS2 in forebrain.