Three Dimensional Structure of the MqsR:MqsA Complex: A Novel TA Pair Comprised of a Toxin Homologous to RelE and an Antitoxin with Unique Properties

One mechanism by which bacteria survive environmental stress is through the formation of bacterial persisters, a sub-population of genetically identical quiescent cells that exhibit multidrug tolerance and are highly enriched in bacterial toxins. Recently, the Escherichia coli gene mqsR (b3022) was identified as the gene most highly upregulated in persisters. Here, we report multiple individual and complex three-dimensional structures of MqsR and its antitoxin MqsA (B3021), which reveal that MqsR:MqsA form a novel toxin:antitoxin (TA) pair. MqsR adopts an α/β fold that is homologous with the RelE/YoeB family of bacterial ribonuclease toxins. MqsA is an elongated dimer that neutralizes MqsR toxicity. As expected for a TA pair, MqsA binds its own promoter. Unexpectedly, it also binds the promoters of genes important for E. coli physiology (e.g., mcbR, spy). Unlike canonical antitoxins, MqsA is also structured throughout its entire sequence, binds zinc and coordinates DNA via its C- and not N-terminal domain. These studies reveal that TA systems, especially the antitoxins, are significantly more diverse than previously recognized and provide new insights into the role of toxins in maintaining the persister state.     

Un nouveau cas de sinusite maxillaire fongique

Résumé Observation d'un cas de sinusite etmoïdo-maxillaire provoqué par l'Aspergillus fumigatus qui fut diagnostiqué par les examens mycologiques et histologiques. Le traitement chirurgical suivi d'une désinfection post-opératoire a amené la guérison.

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Observation of a case of ethmoïdo-maxillary sinusitis, provoked byAspergillus fumigatus and diagnosed by mycological and histological examinations.Surgical treatment followed by post-operative desinfection has brought recovery.

     

Multivariate meta‐analysis with an increasing number of parameters

Meta‐analysis can average estimates of multiple parameters, such as a treatment's effect on multiple outcomes, across studies. Univariate meta‐analysis (UVMA) considers each parameter individually, while multivariate meta‐analysis (MVMA) considers the parameters jointly and accounts for the correlation between their estimates. The performance of MVMA and UVMA has been extensively compared in scenarios with two parameters. Our objective is to compare the performance of MVMA and UVMA as the number of parameters, p, increases. Specifically, we show that (i) for fixed‐effect (FE) meta‐analysis, the benefit from using MVMA can substantially increase as p increases; (ii) for random effects (RE) meta‐analysis, the benefit from MVMA can increase as p increases, but the potential improvement is modest in the presence of high between‐study variability and the actual improvement is further reduced by the need to estimate an increasingly large between study covariance matrix; and (iii) when there is little to no between‐study variability, the loss of efficiency due to choosing RE MVMA over FE MVMA increases as p increases. We demonstrate these three features through theory, simulation, and a meta‐analysis of risk factors for non‐Hodgkin lymphoma.     

In vitro Reaction of Sunflower (Helianthus annuus L.) to the Toxin(s) Produced by Alternaria alternata, the Casual Agent of Brown Leaf Spot

A bioassay system was developed for studying the in vitro reaction of sunflower ( Helianthus annuus L. cv. 'Nanus') against the toxin produced by the virulent pathotype IMI 366417 (1) of the pathogenic fungus Alternaria alternata. Cotyledons from 2-week-old seedlings were cultured on a MS (Murashige and Skoog) medium supplemented with 0.3 μM NAA (α-napthylacetic acid) and 1.3 μM BA (6-benzyladenine). Exponentially growing calli were transferred to selective media containing toxin solutions at various concentrations. The fresh weight of the cultured calli was reduced as the toxin concentration increased, although the viability of the cells, expressed as callus dehydrogenase activity, increased. Selection for toxinresistant genotypes was attempted at 30% toxin concentration, which causes a 90% reduction in callus growth. After one month in culture, 18% of the calli demonstrated resistance to the toxin. However, no plants could be regenerated from those calli after transfer onto a MS medium supplemented with 5.4 μM NAA and 4.4 μM BA. The effect of the toxin purification method on toxin yield and biological activity, as well as its possible mode of cellular action are discussed. The results of these experiments may contribute to a better understanding of the disease mechanism and help establish an efficient selection method of resistant sunflower genotypes.     

Contribution à la technique de l'anti-biogramme anti-fungique

Résumé Les auteurs font état de leur expérience avec une nouvelle technique qu'ils ont mise au point considérant l'antibiogramme anti-fungique d'après Heatley. Cette méthode simple permet d'apporter des renseignements rapides sur le pouvoir anti-fungique des substances chimio-thérapiques ou antibiotiques testées.

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The authors describe a new technic adapting Heatley's method for testing the sensitivity of fungi to chemotherapeutic and antibiotic agents. This is a simple and rapid test of the antifungal activity of various substances.

     

The Molecular Mechanism of Substrate Engagement and Immunosuppressant Inhibition of Calcineurin

Ser/thr phosphatases dephosphorylate their targets with high specificity, yet the structural and sequence determinants of phosphosite recognition are poorly understood. Calcineurin (CN) is a conserved Ca²⁺/calmodulin-dependent ser/thr phosphatase and the target of immunosuppressants, FK506 and cyclosporin A (CSA). To investigate CN substrate recognition we used X-ray crystallography, biochemistry, modeling, and in vivo experiments to study A238L, a viral protein inhibitor of CN. We show that A238L competitively inhibits CN by occupying a critical substrate recognition site, while leaving the catalytic center fully accessible. Critically, the 1.7 Å structure of the A238L-CN complex reveals how CN recognizes residues in A238L that are analogous to a substrate motif, “LxVP.” The structure enabled modeling of a peptide substrate bound to CN, which predicts substrate interactions beyond the catalytic center. Finally, this study establishes that “LxVP” sequences and immunosuppressants bind to the identical site on CN. Thus, FK506, CSA, and A238L all prevent “LxVP”-mediated substrate recognition by CN, highlighting the importance of this interaction for substrate dephosphorylation. Collectively, this work presents the first integrated structural model for substrate selection and dephosphorylation by CN and lays the groundwork for structure-based development of new CN inhibitors.