A Common Ca2+-Driven Interdomain Module Governs Eukaryotic NCX Regulation

Na+/Ca2+ exchanger (NCX) proteins mediate Ca2+-fluxes across the cell membrane to maintain Ca2+ homeostasis in many cell types. Eukaryotic NCX contains Ca2+-binding regulatory domains, CBD1 and CBD2. Ca2+ binding to a primary sensor (Ca3-Ca4 sites) on CBD1 activates mammalian NCXs, whereas CALX, a Drosophila NCX ortholog, displays an inhibitory response to regulatory Ca2+. To further elucidate the underlying regulatory mechanisms, we determined the 2.7 Å crystal structure of mammalian CBD12-E454K, a two-domain construct that retains wild-type properties. In conjunction with stopped-flow kinetics and SAXS (small-angle X-ray scattering) analyses of CBD12 mutants, we show that Ca2+ binding to Ca3-Ca4 sites tethers the domains via a network of interdomain salt-bridges. This Ca2+-driven interdomain switch controls slow dissociation of “occluded” Ca2+ from the primary sensor and thus dictates Ca2+ sensing dynamics. In the Ca2+-bound conformation, the interdomain angle of CBD12 is very similar in NCX and CALX, meaning that the interdomain distances cannot account for regulatory diversity in NCX and CALX. Since the two-domain interface is nearly identical among eukaryotic NCXs, including CALX, we suggest that the Ca2+-driven interdomain switch described here represents a general mechanism for initial conduction of regulatory signals in NCX variants

Conformational space exploration of cryo-EM structures by variability refinement

Cryo-EM observation of biological samples enables visualization of sample heterogeneity, in the form of discrete states that are separable, or continuous heterogeneity as a result of local protein motion before flash freezing. Variability analysis of this continuous heterogeneity describes the variance between a particle stack and a volume, and results in a map series describing the various steps undertaken by the sample in the particle stack. While this observation is absolutely stunning, it is very hard to pinpoint structural details to elements of the maps. In order to bridge the gap between observation and explanation, we designed a tool that refines an ensemble of structures into all the maps from variability analysis. Using this bundle of structures, it is easy to spot variable parts of the structure, as well as the parts that are not moving. Comparison with molecular dynamics simulations highlights the fact that the movements follow the same directions, albeit with different amplitudes. Ligand can also be investigated using this method. Variability refinement is available in the Phenix software suite, accessible under the program name phenix.varref

Shelf-derived mass-transport deposits: origin and significance in the stratigraphic development of trench-slope basins

Continental shelves generally supply large-scale mass-wasting events. Yet, the origin and significance of shelf-derived mass-transport deposits (MTDs) for the tectonostratigraphic evolution of subduction complexes and their trench-slope basins have not been extensively studied. Here, we present high-resolution, outcrop-scale insights on both the nature of the reworked sediments, and their mechanisms of development and emplacement along tectonically active margins, by examining the Middle Miocene shelf-derived MTDs outcropping in the exhumed southern portion of the Hikurangi subduction margin. Results show that periods of repeated tectonic activity (thrust propagation, uplift) in such compressional settings not only affect and control the development of shelfal environments but also drive the recurrent generation and destruction of oversteepened slopes, which in turn, favour the destabilisation and collapses of the shelves and their substratum. Here, these events produced both large-scale, shelf-derived sediment mass-failures and local debris flows, which eventually broke down into a series of coalescing, erosive, genetically linked surging flows downslope. The associated MTDs have a regional footprint, being deposited across several trench-slope basins. Recognition of tectonic activity as another causal mechanism for large-scale shelf failure (in addition to sea-level changes, high-sedimentation fluxes) has implications for both stratigraphic predictions and understanding the tectonostratigraphic evolution of deep-marine fold-and-thrust belts

Contrasting mixed siliciclastic-carbonate shelf-derived gravity-driven systems in compressional intra-slope basins (southern Hikurangi margin, New Zealand)

Along active margins, the combination of predominant tectonic activity and shallow-marine mixed siliciclastic-carbonate source systems developing upon and around actively growing structures challenges traditional source-to-sink models. This study aims to investigate the implications of mixed siliciclastic-carbonate shelfal domains located in contrasting geotectonic settings (thrust forelimb and backlimb) for the development of the concomitant gravity-driven systems beyond the shelf edges. Here, we document the vertical and lateral stratigraphic variabilities of the shelf-derived turbidites and mass-transport deposits (MTDs) at outcrop-scale through the integrated interpretation of photogrammetry, field and taphonomic data from the emerged southern portion of the Hikurangi subduction margin. Results highlight the role and importance of varying structural setting of the sediment source, whereby the different morphologies of the source regions (continent-attached forelimb, continent-detached backlimb) control the development of highly varied shelf-derived gravity-driven depositional systems that interact with the structures across the same confined intra-slope basin. The deposits are tens to a few hundred of meters in thickness and have a lateral extent of several kilometers. The depositional systems are characterized by durations of 1–2 Ma and were primarily controlled by the geometries and tectonic motion of the underlying structures at the shelf edges. Shelf-derived mass-wasting systems occurred on both sides of the actively growing thrust structures and were sourced from both shelfal domains that were attached or detached from the continental domain. When sourced from the backlimbs however, the subsequent MTDs exhibit more complex internal architectures, ultimately recording the dynamic changes in slope gradient, and can therefore be used as proxies for unraveling the tectonic activity of an individual structure. Our study provides new insights to better predict mixed siliciclastic-carbonate depositional settings along active margins, sourced from thrust forelimb and backlimb. These results may be important for deep-marine exploration and tectonostratigraphic reconstruction of fold-and-thrust belts

Épidémiologie des infections à mycobactéries non tuberculeuses d’expression respiratoire en Guyane française, étude rétrospective 2008–2018

International audienceIntroductionL’épidémiologie des infections causées par les mycobactéries non tuberculeuses d’expression respiratoire (MBNTER) est mal connue en Amérique latine, et en Guyane française en particulier. L’objectif principal de cette étude était de déterminer les caractéristiques de ces infections en Guyane. Les objectifs secondaires étaient de déterminer l’incidence des maladies pulmonaires liées aux MBNTER (MBNT-MP), et les caractéristiques spécifiques des malades infectés à Mycobacterium avium complexe (MAC) ou M. abscessus et de ceux infectés par le VIH.MéthodesIl s’agit d’une étude rétrospective observationnelle multicentrique entre 2008 et 2018, réalisée sur tous les hôpitaux de Guyane. Étaient inclus les patients ayant eu au moins une culture positive à MBNTER sur prélèvement respiratoire. Les cas étaient classés en 2 catégories : porteurs non malades et malades dues à une atteinte pulmonaire liée à MBNTER selon les critères définis par l’American Thoracic Society/Infectious Disease Society of America (ATS/IDSA) en 2007.RésultatsSur la période d’étude, 178 cas ont été inclus, parmi lesquels 147 étaient porteurs non malades et 31 malades. Les patients étaient plutôt des hommes (61 %), jeunes (âge médian 49 ans), vivant dans la précarité (64 %) avec des comorbidités respiratoires (33 %) ou une immunodépression avec des CD4 ≤ 50/mm3 dans 39 % des 46 % de patients séropositifs pour le VIH. Les MAC suivies de M. fortuitum puis M. abscessus étaient les plus fréquentes (38 %, 19 % et 6 % respectivement). Le taux d’incidence annuel moyen de MBNT-MP était à 1,07/100 000 habitants par an. La MBNT-MP était significativement associée à l’infection par le VIH, à la dénutrition, et aux espèces MAC et M. abscessus qui représentaient respectivement 81 % et 16 % des maladies pulmonaires à MBNT. La mortalité à un an toutes causes confondues était de 29 % chez les malades.ConclusionIl s’agit de la première étude réalisée sur les infections à MBNTER en Guyane. L’épidémiologie des MBNTER y est spécifique avec une population différente de celle de France métropolitaine. MAC et M. abscessus sont les espèces responsables de maladies respiratoires favorisées par une infection par le VIH, ou par des comorbidités respiratoires et la dénutrition, respectivement. Les caractéristiques chez le séropositif pour le VIH sont différentes et les critères ATS/IDSA n’y sont pas extrapolables rendant le diagnostic difficile. La mortalité est plus élevée en Guyane qu’en France métropolitaine