Localization of subunits in proteasomes from Thermoplasma acidophilum by immunoelectron microscopy

The subunit topography of the Thermoplasma acidophilum proteasome was determined by iminunoelectron microscopy using monospecific antibodies directed against the two constituent subunits (,β). Anti--subunit IgG was found to bind to the outer disks of the cylinder- or barrel-shaped molecule, while the binding sites of the anti-β-subunit IgG were mapped on the two inner rings. Probably the homologues of the two subunits in the compositionally more complex but isomorphous eukaryotic proteasomes occupy equivalent positions.     

Expression of functional Thermoplasma acidophilum proteasomes in Escherichia coli.

The two genes encoding the constituent subunits of the Thermoplasma acidophilum proteasome were expressed in Escherichia coli yielding fully assembled molecules as shown by electron microscopy. The recombinant proteasomes were purified to homogeneity and were shown to have proteolytic activity indistinguishable from proteasomes isolated from T. acidophilum.     

Addition of the immunostimulatory oligonucleotide IMT504 to a seasonal flu vaccine increases hemagglutinin antibody titers in young adult and elder rats, and expands the anti-hemagglutinin antibody repertoire

Flu vaccines are partially protective in infants and elder people. New adjuvants such as immunostimulatory oligonucleotides (ODNs) are strong candidates to solve this problem, because a combination with several antigens has demonstrated effectiveness. Here, we report that IMT504, the prototype of a major class of immunostimulatory ODNs, is a potent adjuvant of the influenza vaccine in young adult and elderly rats. Flu vaccines that use virosomes or whole viral particles as antigens were combined with IMT504 and injected in rats. Young adult and elderly animals vaccinated with IMT504-adjuvated preparations reached antibody titers 20-fold and 15-fold higher than controls, respectively. Antibody titers remained high throughout a 120 day-period. Animals injected with the IMT504-adjuvated vaccine showed expansion of the anti-hemagglutinin antibody repertoire and a significant increase in the antibody titer with hemagglutination inhibition capacity when confronted to viral strains included or not in the vaccine. This indicates that the addition of IMT504 in flu vaccines may contribute to the development of significant cross-protective immune response against shifted or drifted flu strains.     

The catalytic activity of Ubp6 enhances maturation of the proteasomal regulatory particle

The 26S proteasome is a 2.5 MDa macromolecular machine responsible for targeted protein degradation. Recently, four chaperones were identified that promote the assembly of the 19S regulatory particle (RP). Here, we probe the dynamic architecture of the proteasome by applying quantitative proteomics and mass spectrometry (MS) of intact complexes to provide a detailed characterization of how Ubp6 assists this assembly process. Our MS data demonstrate stoichiometric binding of chaperones and Ubp6 to the basal part of the RP. Genetic interactions of Ubp6 with Hsm3, but not with the other chaperones, indicate a functional overlay with Hsm3. Our biochemical data identified Ubp6 as an additional member of the Hsm3 module. Deletions of ubp6 with hsm3 perturb 26S proteasome assembly, which we attribute to an accumulation of ubiquitylated substrates on these assembly precursors. We therefore propose that Ubp6 facilitates proteasomal assembly by clearing ubiquitylated substrates from assembly precursors by its deubiquitylating activity.     

Peptidomics and peptide hormone processing in the Drosophila midgut

Peptide hormones are key messengers in the signaling network between the nervous system, endocrine glands, energy stores and the gastrointestinal tract that regulates feeding and metabolism. Studies on the Drosophila nervous system have uncovered parallels and homologies in homeostatic peptidergic signaling between fruit flies and vertebrates. Yet, the role of enteroendocrine peptides in the regulation of feeding and metabolism has not been explored, with research hampered by the unknown identity of peptides produced by the fly's intestinal tract. We performed a peptidomic LC/MS analysis of the fruit fly midgut containing the enteroendocrine cells. By MS/MS fragmentation, we found 24 peptides from 9 different preprohormones in midgut extracts, including MIP-4 and 2 forms of AST-C. DH(31), CCHamide1 and CCHamide2 are biochemically characterized for the first time. All enteroendocrine peptides represent brain-gut peptides, and apparently are processed by Drosophila prohormone convertase 2 (AMON) as suggested by impaired peptide detectability in amon mutants and localization of amon-driven GFP to enteroendocrine cells. Because of its genetic amenability and peptide diversity, Drosophila provides a good model system to study peptide signaling. The identification of enteroendocrine peptides in the fruit fly provides a platform to address functions of gut peptide hormones in the regulation of feeding and metabolism.     

Automated segmentation of electron tomograms for a quantitative description of actin filament networks

Cryo-electron tomography allows to visualize individual actin filaments and to describe the three-dimensional organization of actin networks in the context of unperturbed cellular environments. For a quantitative characterization of actin filament networks, the tomograms must be segmented in a reproducible manner. Here, we describe an automated procedure for the segmentation of actin filaments, which combines template matching with a new tracing algorithm. The result is a set of lines, each one representing the central line of a filament. As demonstrated with cryo-tomograms of cellular actin networks, these line sets can be used to characterize filament networks in terms of filament length, orientation, density, stiffness (persistence length), or the occurrence of branching points.