Structural insights into chaperone addiction of toxin-antitoxin systems

International audienceSecB chaperones assist protein export by binding both unfolded proteins and the SecA motor. Certain SecB homologs can also control toxin-antitoxin (TA) systems known to modulate bacterial growth in response to stress. In such TA-chaperone (TAC) systems, SecB assists the folding and prevents degradation of the antitoxin, thus facilitating toxin inhibition. Chaperone dependency is conferred by a C-terminal extension in the antitoxin known as chaperone addiction (ChAD) sequence, which makes the antitoxin aggregation-prone and prevents toxin inhibition. Using TAC of Mycobacterium tuberculosis, we present the structure of a SecB-like chaperone bound to its ChAD peptide. We find differences in the binding interfaces when compared to SecB–SecA or SecB-preprotein complexes, and show that the antitoxin can reach a functional form while bound to the chaperone. This work reveals how chaperones can use discrete surface binding regions to accommodate different clients or partners and thereby expand their substrate repertoire and functions

The North American tree-ring fire-scar network

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree-ring fire scars provide valuable perspectives on fire regimes, including centuries-long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree-ring fire-scar network (NAFSN), which contains 2562 sites, >37,000 fire-scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000-m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire-scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under-sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non-Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually- to sub-annually-resolved tree-ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America

Changes in Body Weight and Psychotropic Drugs: A Systematic Synthesis of the Literature

<div><h3>Introduction</h3><p>Psychotropic medication use is associated with weight gain. While there are studies and reviews comparing weight gain for psychotropics within some classes, clinicians frequently use drugs from different classes to treat psychiatric disorders.</p> <h3>Objective</h3><p>To undertake a systematic review of all classes of psychotropics to provide an all encompassing evidence-based tool that would allow clinicians to determine the risks of weight gain in making both intra-class and interclass choices of psychotropics.</p> <h3>Methodology and Results</h3><p>We developed a novel hierarchical search strategy that made use of systematic reviews that were already available. When such evidence was not available we went on to evaluate randomly controlled trials, followed by cohort and other clinical trials, narrative reviews, and, where necessary, clinical opinion and anecdotal evidence. The data from the publication with the highest level of evidence based on our hierarchical classification was presented. Recommendations from an expert panel supplemented the evidence used to rank these drugs within their respective classes. Approximately 9500 articles were identified in our literature search of which 666 citations were retrieved. We were able to rank most of the psychotropics based on the available evidence and recommendations from subject matter experts. There were few discrepancies between published evidence and the expert panel in ranking these drugs.</p> <h3>Conclusion</h3><p>Potential for weight gain is an important consideration in choice of any psychotropic. This tool will help clinicians select psychotropics on a case-by-case basis in order to minimize the impact of weight gain when making both intra-class and interclass choices.</p> </div

AIDS grief and multiple loss: the experiences of individuals within an AIDS service organization

This qualitative study identified the experiences of AIDS grief and multiple loss by eight individuals within an AIDS service organization in the province of Alberta. Collaborative, ethnographic, and narrative approaches in research design and analysis were used to connect and analyze audio-taped and transcribed interviews. Critical case sampling assisted in choosing participants who had a minimum of one year involvement with this organization, and who had experienced multiple losses and deaths from AIDS. Participants represented multiple roles within this organization including client, board, volunteer, management, counselor, and administrative support staff. Interviews were analyzed for repeating themes and reconstructed into a narrative life story for each participant. These themes and stories were compared between participants resulting in an ethnographic analysis about multiple loss within this community and culture. The central challenge, woven throughout the individual and organizational history, was 'balancing pain of loss with hope and commitment'. Participants described four core themes emerging from this central challenge: 'layers and cycles' of multiple losses; 'not enough or limited time' to grieve; which creates an urgency to 'fight'; in a setting where there are normative 'complex and blurred roles and relationships'. A cyclical process of coping was identified: tension and emotions build; episodic expressions of grief occur (over reaction and out of proportion expressions, and black humor); numbness develops (due to being overwhelmed); heightened anxiety & catastrophic thinking set in (associated with anticipation of greater loss and especially noted in those HIV positive); efforts to distance oneself occur (temporary to permanent which provide opportunity to integrate, reflect and replenish energy) and protective strategies are created to reduce the impact of multiple loss; memorializing and sharing with the select few who understand occurs; and there is expeditious reinvestment of feelings into a recommitment (which helps to honor those who have died and contribute to those who now need support). Participants highlight the consequences of AIDS grief on individual and organizational functioning, and identify/recommend strategies for resilient coping. The diverse social and organization factors impacting AIDS grief and multiple loss were also identified.Arts, Faculty ofSocial Work, School ofGraduat

PLACE DU CHIEN DANS LA LEISHMANIOSE EN FRANCE (ASPECTS EPIDEMIOLOGIQUE, DIAGNOSTIQUE, THERAPEUTIQUE ET PROPHYLACTIQUE)

LYON1-BU Santé (693882101) / SudocSudocFranceF

A novel algorithm identifies stress-induced alterations in mitochondrial connectivity and inner membrane structure from confocal images

<div><p>Mitochondria exist as a highly interconnected network that is exquisitely sensitive to variations in nutrient availability, as well as a large array of cellular stresses. Changes in length and connectivity of this network, as well as alterations in the mitochondrial inner membrane (cristae), regulate cell fate by controlling metabolism, proliferation, differentiation, and cell death. Given the key roles of mitochondrial dynamics, the process by which mitochondria constantly fuse and fragment, the measure of mitochondrial length and connectivity provides crucial information on the health and activity of various cell populations. However, despite the importance of accurately measuring mitochondrial networks, the tools required to rapidly and accurately provide this information are lacking. Here, we developed a novel probabilistic approach to automatically measure mitochondrial length distribution and connectivity from confocal images. This method accurately identified mitochondrial changes caused by starvation or the inhibition of mitochondrial function. In addition, we successfully used the algorithm to measure changes in mitochondrial inner membrane/matrix occurring in response to Complex III inhibitors. As cristae rearrangements play a critical role in metabolic regulation and cell survival, this provides a rapid method to screen for proteins or compounds affecting this process. The algorithm will thus provide a robust tool to dissect the molecular mechanisms underlying the key roles of mitochondria in the regulation of cell fate.</p></div

Overview of the algorithm.

<p>(A-B) Several distinct topologies can be assigned to a single mitochondrial network. U2OS cells were stained for the mitochondrial marker TOM20 and imaged. The lower panels show two distinct possible topologies for the same mitochondrial cluster (boxed area in top left panel (A)). Colour lines represent individual mitochondrial tubules; green circles, junctions (A). Mitochondrial length was then quantified from 7 cells by measuring the distance between each connexion (B; Blue) or the longest possible mitochondria to which the other mitochondria are connected (B; Red). (C) Overview of the analysis process. Grayscale confocal images are first converted into binary images (see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005612#sec009" target="_blank">Methods</a>) then fed to the algorithm (1). The mitochondrial network is then separated into clusters of overlapping mitochondria that are analysed by the structure interpreter (2). The resulting structural information (ends, tubules, junctions) is then used to generate the probability of the different possible configurations for each cluster (3). The distributions are then used to generate the overall distribution probability for the cell (4). See also <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005612#pcbi.1005612.s003" target="_blank">S3 Fig</a>.</p

AA but not Myxo induces mitochondrial fragmentation in U2OS cells.

<p>(A-B) OPA1 KO mitochondria are fragmented. WT and OPA1 KO MEFs were stained using the mitochondrial marker TOM20 and imaged. Mitochondrial distributions (A) and EMD quantification of the shift in distribution between WT and KO cells (B; WT and OPA1 KO, experimental variation; WT vs KO, variation between genotypes) were then determined as for EBSS treatments (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005612#pcbi.1005612.g004" target="_blank">Fig 4</a>). Data is expressed as the average of 3 independent experiments ± SD. *** p<0.001. (C) Changes in <i>E</i>_<i>C</i> and <i>J/E</i> correlate with mitochondrial fragmentation. Data is expressed as the average of 3 independent experiments ± S.D. *** p<0.001. (D-E) Decreased mitochondrial length in U2OS cells treated with the Complex III inhibitor AA. Cells were treated for 4 hours with AA or Myxo, then fixed and analysed as in (A-B). Data is expressed as the average of 3 independent experiments ± SD. *** p<0.001. For EMD scores (E), Ctrl, AA and Myxo refer to the experimental variation while AA/Myxo vs Ctrl and AA vs Myxo measure the change in distribution between treatments. (F) AA, but not Myxo, decreases mitochondrial connectivity as measured by <i>E</i>_<i>C</i> and <i>J/E</i> values. Data is expressed as the average of 3 independent experiments ± S.D. *** p<0.001, ** p<0.01, * p<0.05 compared with the control or AA where indicated. (G-I) Changes in specific mitochondrial structures following AA treatment. Donuts (mitochondria looped on themselves) were measured by the algorithm (G) or manually (H) and the result expressed as the average of 3 independent experiments ± S.D. Blobs (isolated mitochondria (<i>E</i>_<i>C</i> = 3) with a length <1 μm) were measured using the algorithm (I). Short isolated mitochondria with lengths between 1 and 2 μm, were also increased following AA treatment. Data is expressed as the average of 3 independent experiments ± S.D. *** p<0.001, ** p<0.01 compared to control. (J) Relationship between connectivity and length across different experimental conditions in individual cells. <i>J/E</i> ratios were used as the connectivity parameter. For length, we used the number of mitochondria in the 1 μm bin because this value correlates well with mitochondrial fragmentation. However to have an increasing value with increasing length, we used 1/this number. To allow comparison between experiments, all values were normalised to the control for that experiment. The shaded areas represent 1 SD and 2 SD from the control values. Individual cells from at least 3 experiments/conditions are shown.</p

The algorithm identifies mitochondrial length and connectivity in computer-generated images.

<p>Three distinct types of distributions were used to test the algorithm: a simple Gaussian (D1), a double Gaussian (D2) and a distribution reflecting the distribution found in fibroblasts (D3). Each image (500 pixels x 500 pixels) contains a defined number of mitochondria (between 10 and 500). A representative example for each distribution (300 mitochondria) is shown in (A) with the input distribution in green, the calculated distribution in blue and the confidence interval in grey. (B) Schematic representation of the different structural element of the mitochondrial network that are analysed by the algorithm. (C-D) Mitochondrial connectivity increases with the number of mitochondria in computer-generated images. (C) The proportion of each type of element was calculated in D3 distributions with increasing number of mitochondria and expressed as a percent of the total number of structural elements ± S.D. of at least 45 images/condition. (D) Alternatively, we calculated <i>E</i>_<i>C</i> values for the 3 distribution types. (E) EMD values between the input distribution and the algorithm-generated distribution for the different distributions types. Shown is the average of at least 45 images/condition ± S.D.</p