NMR solution structure of Ole e 6, a major allergen from olive tree pollen

Ole e 6 is a pollen protein from the olive tree (Olea europaea) that exhibits allergenic activity with a high prevalence among olive-allergic individuals. The three-dimensional structure of Ole e 6 has been determined in solution by NMR methods. This is the first experimentally determined structure of an olive tree pollen allergen. The structure of this 50-residue protein is based on 486 upper limit distance constraints derived from nuclear Overhauser effects and 24 torsion angle restraints. The global fold of Ole e 6 consists of two nearly antiparallel alpha-helices, spanning residues 3-19 and 23-33, that are connected by a short loop and followed by a long, unstructured C-terminal tail. Viewed edge-on, the structured N terminus has a dumbbell-like shape with the two helices on the outside and with the hydrophobic core, mainly composed of 3 aromatic and 6 cysteine residues, on the inside. All the aromatic rings lie on top of and pack against the three disulfide bonds. The lack of thermal unfolding, even at 85 degrees C, indicates a high conformational stability. Based on the analysis of the molecular surface, we propose five plausible epitopes for IgE recognition. The results presented here provide the structural foundation for future experiments to verify the antigenicity of the proposed epitopes, as well as to design novel hypoallergenic forms of the protein suitable for diagnosis and treatment of type-I allergies. In addition, three-dimensional structure features of Ole e 6 are discussed to provide a basis for future functional studies.     

Leishmanial infection: analysis of its first steps. A review

The first steps in leishmaniasis are critical in determining the evolution of the disease. Major advances have recently been done in understanding this crucial moment. Fundamental research in parasite-vector interaction, parasite biology, insect saliva, and vertebrate host response have shed new light and uncovered a most fascinating and complex moment in leishmaniasis. We review here some of these aspects and we try to connect them in a logical framework.     

Regulation of the myosin-directed chaperone UNC-45 by a novel E3/E4-multiubiquitylation complex in C. elegans

The organization of the motor protein myosin into motile cellular structures requires precise temporal and spatial control. Caenorhabditis elegans UNC-45 facilitates this by functioning both as a chaperone and as a Hsp90 cochaperone for myosin during thick filament assembly. Consequently, mutations in C. elegans unc-45 result in paralyzed animals with severe myofibril disorganization in striated body wall muscles. Here, we report a new E3/E4 complex, formed by CHN-1, the C. elegans ortholog of CHIP (carboxyl terminus of Hsc70-interacting protein), and UFD-2, an enzyme known to have ubiquitin conjugating E4 activity in yeast, as necessary and sufficient to multiubiquitylate UNC-45 in vitro. The phenotype of unc-45 temperature-sensitive animals is partially suppressed by chn-1 loss of function, while UNC-45 overexpression in worms deficient for chn-1 results in severely disorganized muscle cells. These results identify CHN-1 and UFD-2 as a functional E3/E4 complex and UNC-45 as its physiologically relevant substrate.     

Fine needle aspiration appearance of extragastrointestinal stromal tumor. A case report

BACKGROUND: Gastrointestinal stromal tumors (GISTs) rarely develop outside the digestive tract and in the soft tissues of abdomen and retroperitoneum. Such tumors are designated extra-GISTs (EGISTs). Cytologic and immunocytochemical features of a case of EGIST are reported. CASE: A 54-year-old woman presented with a peritoneal mass, diameter 22 cm, adherent to the omentum and without a connection to the digestive tract. Fine needle aspiration biopsy (FNAB) of the excised tumor showed high cellularity in two patterns: monotonous spindle cells were intermingled with a mildly atypical epithelioid component. Immunocytochemistry performed on cytospins revealed reactivity for c-kit (CD117), CD34 and smooth muscle actin and negativity for S-100. The findings were concordant with a histologic diagnosis of EGIST. CONCLUSION: EGISTs are infrequent neoplasms and can be diagnosed in FNAB samples. The clinical/radiologic setting must be considered together with the cytologic features. Immunocytochemistry is a clue to the diagnosis when it detects c-kit reactivity.     

Spindle orientation in Saccharomyces cerevisiae depends on the transport of microtubule ends along polarized actin cables

Microtubules and actin filaments interact and cooperate in many processes in eukaryotic cells, but the functional implications of such interactions are not well understood. In the yeast Saccharomyces cerevisiae, both cytoplasmic microtubules and actin filaments are needed for spindle orientation. In addition, this process requires the type V myosin protein Myo2, the microtubule end-binding protein Bim1, and Kar9. Here, we show that fusing Bim1 to the tail of the Myo2 is sufficient to orient spindles in the absence of Kar9, suggesting that the role of Kar9 is to link Myo2 to Bim1. In addition, we show that Myo2 localizes to the plus ends of cytoplasmic microtubules, and that the rate of movement of these cytoplasmic microtubules to the bud neck depends on the intrinsic velocity of Myo2 along actin filaments. These results support a model for spindle orientation in which a Myo2-Kar9-Bim1 complex transports microtubule ends along polarized actin cables. We also present data suggesting that a similar process plays a role in orienting cytoplasmic microtubules in mating yeast cells.     

Leishmania amazonensis infection: a comparison of in vivo leishmanicidal mechanisms between immunized and naive infected BALB/c mice.

In vitro studies have shown that both macrophage activation and destruction of parasitized macrophages lead to leishmania destruction. The relative role played by such mechanisms in vivo have not been properly evaluated. We took advantage of the model of intravenous immunization with solubilized leishmanial antigen which renders partially resistant the otherwise highly susceptible BALB/c mice to address this issue avoiding the interference of different genetic backgrounds. Leishmania destruction occurred in three situations: destruction of the parasitized macrophage, which were in close contact with lymphocytes or eosinophils; extracellular damage, always surrounded by small foci of granulocytes; and parasite damage inside activated macrophages. Destruction of the parasitized macrophages was frequently seen in immunized and protected animals. Our observations suggest that destruction of parasite-loaded macrophages is an important mechanism of host protection in experimental cutaneous leishmaniasis.     

De novo folding of GFP fusion proteins: high efficiency in eukaryotes but not in bacteria

Eukaryotic genomes encode a considerably higher fraction of multi-domain proteins than their prokaryotic counterparts. It has been postulated that efficient co-translational and sequential domain folding has facilitated the explosive evolution of multi-domain proteins in eukaryotes by the recombination of pre-existent domains. Here, we tested whether eukaryotes and bacteria differ generally in the folding efficiency of multi-domain proteins generated by domain recombination. To this end, we compared the folding behavior of a series of recombinant proteins comprised of green fluorescent protein (GFP) fused to four different robustly folding proteins through six different linkers upon expression in Escherichia coli and the yeast Saccharomyces cerevisiae. We found that, unlike yeast, bacteria are remarkably inefficient at folding these fusion proteins, even at comparable levels of expression. In vitro and in vivo folding experiments demonstrate that the GFP domain imposes significant constraints on de novo folding of its fusion partners in bacteria, consistent with a largely post-translational folding mechanism. This behavior may result from an interference of GFP with adjacent domains during folding due to the particular topology of the beta-barrel GFP structure. By following the accumulation of enzymatic activity, we found that the rate of appearance of correctly folded fusion protein per ribosome is indeed considerably higher in yeast than in bacteria.     

Degradation of Hof1 by SCF(Grr1) is important for actomyosin contraction during cytokinesis in yeast

SCF-type (SCF: Skp1-Cullin-F-box protein complex) E3 ligases regulate ubiquitin-dependent degradation of many cell cycle regulators, mainly at the G1/S transition. Here, we show that SCF(Grr1) functions during cytokinesis by degrading the PCH protein Hof1. While Hof1 is required early in mitosis to assemble a functional actomyosin ring, it is specifically degraded late in mitosis and remains unstable during the entire G1 phase of the cell cycle. Degradation of Hof1 depends on its PEST motif and a functional 26S proteasome. Interestingly, degradation of Hof1 is independent of APC(Cdh1), but instead requires the SCF(Grr1) E3 ligase. Grr1 is recruited to the mother-bud neck region after activation of the mitotic-exit network, and interacts with Hof1 in a PEST motif-dependent manner. Our results also show that downregulation of Hof1 at the end of mitosis is necessary to allow efficient contraction of the actomyosin ring and cell separation during cytokinesis. SCF(Grr1)-mediated degradation of Hof1 may thus represent a novel mechanism to couple exit from mitosis with initiation of cytokinesis.     

Efficient production of native actin upon translation in a bacterial lysate supplemented with the eukaryotic chaperonin TRiC

Recombinant expression of actin in bacteria results in non-native species that aggregate into inclusion bodies. Actin is a folding substrate of TRiC, the chaperonin of the eukaryotic cytosol. By employing bacterial in vitro translation lysates supplemented with purified chaperones, we have found that TRiC is the only eukaryotic chaperone necessary for correct folding of newly translated actin. The actin thus produced binds deoxyribonuclease I and polymerizes into filaments, hallmarks of its native state. In contrast to its rapid folding in the eukaryotic cytosol, actin translated in TRiC-supplemented bacterial lysate folds with slower kinetics, resembling the kinetics upon refolding from denaturant. Lysate supplementation with the bacterial chaperonin GroEL/ES or the DnaK/DnaJ/GrpE chaperones leads to prevention of actin aggregation, yet fails to support its correct folding. This combination of in vitro bacterial translation and TRiC-assisted folding allows a detailed analysis of the mechanisms necessary for efficient actin folding in vivo. In addition, it provides a robust alternative for the production of substantial amounts of eukaryotic proteins that otherwise misfold or lead to cellular toxicity upon expression in heterologous hosts.