Structure of the theta subunit of Escherichia coli DNA polymerase III in complex with the epsilon subunit

The catalytic core of Escherichia coli DNA polymerase III contains three tightly associated subunits, the alpha, epsilon, and theta subunits. The theta subunit is the smallest and least understood subunit. The three-dimensional structure of theta in a complex with the unlabeled N-terminal domain of the epsilon subunit, epsilon186, was determined by multidimensional nuclear magnetic resonance spectroscopy. The structure was refined using pseudocontact shifts that resulted from inserting a lanthanide ion (Dy3+, Er3+, or Ho3+) at the active site of epsilon186. The structure determination revealed a three-helix bundle fold that is similar to the solution structures of theta in a methanol-water buffer and of the bacteriophage P1 homolog, HOT, in aqueous buffer. Conserved nuclear Overhauser enhancement (NOE) patterns obtained for free and complexed theta show that most of the structure changes little upon complex formation. Discrepancies with respect to a previously published structure of free theta (Keniry et al., Protein Sci. 9:721-733, 2000) were attributed to errors in the latter structure. The present structure satisfies the pseudocontact shifts better than either the structure of theta in methanol-water buffer or the structure of HOT. satisfies these shifts. The epitope of epsilon186 on theta was mapped by NOE difference spectroscopy and was found to involve helix 1 and the C-terminal part of helix 3. The pseudocontact shifts indicated that the helices of theta are located about 15 A or farther from the lanthanide ion in the active site of epsilon186, in agreement with the extensive biochemical data for the theta-epsilon system.     

Alternate recruitment of signal recognition particle and trigger factor to the signal sequence of a growing nascent polypeptide

Different from cytoplasmic membrane proteins, presecretory proteins of bacteria usually do not require the signal recognition particle for targeting to the Sec translocon. Nevertheless signal sequences of presecretory proteins have been found in close proximity to signal recognition particle immediately after they have emerged from the ribosome. We show here that at the ribosome, the molecular environment of a signal sequence depends on the nature of downstream sequence elements that can cause an alternate recruitment of signal recognition particle and the ribosome-associated chaperone Trigger factor to a growing nascent chain. While signal recognition particle and Trigger factor might remain bound to the same ribosome, both ligands are clearly able to displace each other from a nascent chain. The data also imply that a signal sequence owes its molecular environment to the fact that it remains closely apposed to the ribosomal exit site during growth of a nascent secretory protein.     

Evidence of leopard predation on bonobos (Pan paniscus)

Current models of social organization assume that predation is one of the major forces that promotes group living in diurnal primates. As large body size renders some protection against predators, gregariousness of great apes and other large primate species is usually related to other parameters. The low frequency of observed cases of nonhuman predation on great apes seems to support this assumption. However, recent efforts to study potential predator species have increasingly accumulated direct and indirect evidence of predation by leopards (Panthera pardus) on chimpanzees and gorillas. The following report provides the first evidence of predation by a leopard on bonobos (Pan paniscus).     

Reinforcement of cancer immunotherapy by adoptive transfer of cblb-deficient CD8+ T cells combined with a DC vaccine

The success of cancer immunotherapy is limited by potent endogenous immune-evasion mechanisms, which are at least in part mediated by transforming growth factor-β (TGF-β). The E3 ubiquitin ligase Cbl-b is a key regulator of T cell activation and is established to regulate TGF-β sensitivity. cblb-deficient animals reject tumors via CD8(+) T cells, which make Cbl-b an ideal target for improvement of adoptive T-cell transfer (ATC) therapy. In this study, we show that cblb-deficient CD8(+) T cells are hyper-responsive to T-cell receptor (TCR)/CD28-stimulation and are in part protected against the negative cues induced by TGF-β in vitro. Notably, adoptive transfer of polyclonal, non-TCR transgenic cblb-deficient CD8(+) T cells is not sufficient to reject B16-ova or EG7 tumors in vivo. Thus, cblb-deficient ATC requires proper in vivo re-activation by a dendritic cell (DC) vaccine. In strict contrast to ATC monotherapy, this approach delayed tumor outgrowth and significantly increased survival rates, which is paralleled by increased CD8(+) T-cells infiltration to the tumor site and enrichment of ova-specific and interferon-γ (IFN-γ)-secreting CD8(+) T cell in the draining lymph node (LN). Moreover, CD8(+) T cells from cblb-deficient mice vaccinated with the DC vaccine show increased cytolytic activity in vivo. In summary, our data using cblb-deficient polyclonal, non-TCR-transgenic adoptively transferred CD8(+) T cells into immuno-competent non-lymphodepleted recipients suggest that targeting Cbl-b might serve as a novel 'adjuvant approach', suitable to augment the effectiveness of established anti-cancer immunotherapies.     

5-alpha-reductase type I (SRD5A1) is up-regulated in non-small cell lung cancer but does not impact proliferation, cell cycle distribution or apoptosis

Background  

Non-small cell lung cancer (NSCLC) is one of the most frequent malignancies and has a high mortality rate due to late detection and lack of efficient treatments. Identifying novel drug targets for this indication may open the way for new treatment strategies. Comparison of gene expression profiles of NSCLC and normal adjacent tissue (NAT) allowed to determine that 5-alpha-reductase type I (SRD5A1) was up-regulated in NSCLC compared to NAT. This raised the question whether SRD5A1 was involved in sustained proliferation and survival of NSCLC.     

The IAP-antagonist ARTS initiates caspase activation upstream of cytochrome C and SMAC/Diablo

ARTS (Sept4_i2) is a pro-apoptotic tumor suppressor protein that functions as an antagonist of X-linked IAP (XIAP) to promote apoptosis. It is generally thought that mitochondrial outer membrane permeabilization (MOMP) occurs before activation of caspases and is required for it. Here, we show that ARTS initiates caspase activation upstream of MOMP. In living cells, ARTS is localized to the mitochondrial outer membrane. In response to apoptotic signals, ARTS translocates rapidly to the cytosol in a caspase-independent manner, where it binds XIAP and promotes caspase activation. This translocation precedes the release of cytochrome C and SMAC/Diablo, and ARTS function is required for the normal timing of MOMP. We also show that ARTS-induced caspase activation leads to cleavage of the pro-apoptotic Bcl-2 family protein Bid, known to promote MOMP. We propose that translocation of ARTS initiates a first wave of caspase activation that can promote MOMP. This leads to the subsequent release of additional mitochondrial factors, including cytochrome C and SMAC/Diablo, which then amplifies the caspase cascade and causes apoptosis.     

Flying at no mechanical energy cost: disclosing the secret of wandering albatrosses

ALBATROSSES DO SOMETHING THAT NO OTHER BIRDS ARE ABLE TO DO: fly thousands of kilometres at no mechanical cost. This is possible because they use dynamic soaring, a flight mode that enables them to gain the energy required for flying from wind. Until now, the physical mechanisms of the energy gain in terms of the energy transfer from the wind to the bird were mostly unknown. Here we show that the energy gain is achieved by a dynamic flight manoeuvre consisting of a continually repeated up-down curve with optimal adjustment to the wind. We determined the energy obtained from the wind by analysing the measured trajectories of free flying birds using a new GPS-signal tracking method yielding a high precision. Our results reveal an evolutionary adaptation to an extreme environment, and may support recent biologically inspired research on robotic aircraft that might utilize albatrosses' flight technique for engineless propulsion.     

Characterization of HLA class II/peptide-TCR interactions of the immunodominant T cell epitope in Art v 1, the major mugwort pollen allergen

More than 95% of mugwort pollen-allergic individuals are sensitized to Art v 1, the major allergen in mugwort pollen. Interestingly, the CD4 T cell response to Art v 1 involves only one single immunodominant peptide, Art v 1(25-36) (KCIEWEKAQHGA), and is highly associated with the expression of HLA-DR1. Therefore, we investigated the molecular basis of this unusual immunodominance among allergens. Using artificial APC expressing exclusively HLA-DRB1*0101 and HLA-DRA*0101, we formally showed that DR1 acts as restriction element for Art v 1(25-36)-specific T cell responses. Further assessment of binding of Art v 1(25-36) to artificial HLA-DR molecules revealed that its affinity was high for HLA-DR1. Amino acid I27 was identified as anchor residue interacting with DR molecules in pocket P1. Additionally, Art v 1(25-36) bound with high affinity to HLA-DRB1*0301 and *0401, moderately to HLA-DRB1*1301 and HLA-DRB5*0101, and weakly to HLA-DRB1*1101 and *1501. T cell activation was also inducible by Art v 1(25-36)-loaded, APC-expressing HLA molecules other than DR1, indicating degeneracy of peptide binding and promiscuity of TCR recognition. Specific binding of HLA-DRB1*0101 tetramers containing Art v 1(19-36) allowed the identification of Art v 1(25-36)-specific T cells by flow cytometry. In summary, the immunodominance of Art v 1(25-36) relies on its affinity to DR1, but is not dictated by it. Future investigations at the molecular HLA/peptide/TCR and cellular level using mugwort pollen allergy as a disease model may allow new insights into tolerance and pathomechanisms operative in type I allergy, which may instigate new, T cell-directed strategies in specific immunotherapy.