The Unconventional Xer Recombination Machinery of Streptococci/Lactococci

Homologous recombination between circular sister chromosomes during DNA replication in bacteria can generate chromosome dimers that must be resolved into monomers prior to cell division. In Escherichia coli, dimer resolution is achieved by site-specific recombination, Xer recombination, involving two paralogous tyrosine recombinases, XerC and XerD, and a 28-bp recombination site (dif) located at the junction of the two replication arms. Xer recombination is tightly controlled by the septal protein FtsK. XerCD recombinases and FtsK are found on most sequenced eubacterial genomes, suggesting that the Xer recombination system as described in E. coli is highly conserved among prokaryotes. We show here that Streptococci and Lactococci carry an alternative Xer recombination machinery, organized in a single recombination module. This corresponds to an atypical 31-bp recombination site (difSL) associated with a dedicated tyrosine recombinase (XerS). In contrast to the E. coli Xer system, only a single recombinase is required to recombine difSL, suggesting a different mechanism in the recombination process. Despite this important difference, XerS can only perform efficient recombination when difSL sites are located on chromosome dimers. Moreover, the XerS/difSL recombination requires the streptococcal protein FtsKSL, probably without the need for direct protein-protein interaction, which we demonstrated to be located at the division septum of Lactococcus lactis. Acquisition of the XerS recombination module can be considered as a landmark of the separation of Streptococci/Lactococci from other firmicutes and support the view that Xer recombination is a conserved cellular function in bacteria, but that can be achieved by functional analogs

A Family of Plasmodesmal Proteins with Receptor-Like Properties for Plant Viral Movement Proteins

Plasmodesmata (PD) are essential but poorly understood structures in plant cell walls that provide symplastic continuity and intercellular communication pathways between adjacent cells and thus play fundamental roles in development and pathogenesis. Viruses encode movement proteins (MPs) that modify these tightly regulated pores to facilitate their spread from cell to cell. The most striking of these modifications is observed for groups of viruses whose MPs form tubules that assemble in PDs and through which virions are transported to neighbouring cells. The nature of the molecular interactions between viral MPs and PD components and their role in viral movement has remained essentially unknown. Here, we show that the family of PD-located proteins (PDLPs) promotes the movement of viruses that use tubule-guided movement by interacting redundantly with tubule-forming MPs within PDs. Genetic disruption of this interaction leads to reduced tubule formation, delayed infection and attenuated symptoms. Our results implicate PDLPs as PD proteins with receptor-like properties involved the assembly of viral MPs into tubules to promote viral movement

Tubule-Guided Cell-to-Cell Movement of a Plant Virus Requires Class XI Myosin Motors

Cell-to-cell movement of plant viruses occurs via plasmodesmata (PD), organelles that evolved to facilitate intercellular communications. Viral movement proteins (MP) modify PD to allow passage of the virus particles or nucleoproteins. This passage occurs via several distinct mechanisms one of which is MP-dependent formation of the tubules that traverse PD and provide a conduit for virion translocation. The MP of tubule-forming viruses including Grapevine fanleaf virus (GFLV) recruit the plant PD receptors called Plasmodesmata Located Proteins (PDLP) to mediate tubule assembly and virus movement. Here we show that PDLP1 is transported to PD through a specific route within the secretory pathway in a myosin-dependent manner. This transport relies primarily on the class XI myosins XI-K and XI-2. Inactivation of these myosins using dominant negative inhibition results in mislocalization of PDLP and MP and suppression of GFLV movement. We also found that the proper targeting of specific markers of the Golgi apparatus, the plasma membrane, PD, lipid raft subdomains within the plasma membrane, and the tonoplast was not affected by myosin XI-K inhibition. However, the normal tonoplast dynamics required myosin XI-K activity. These results reveal a new pathway of the myosin-dependent protein trafficking to PD that is hijacked by GFLV to promote tubule-guided transport of this virus between plant cells

Cysteine Redox Potential Determines Pro-Inflammatory IL-1β Levels

Cysteine (Cys) and its disulfide, cystine (CySS) represent the major extracellular thiol/disulfide redox control system. The redox potential (E(h)) of Cys/CySS is centered at approximately -80 mV in the plasma of healthy adults, and oxidation of E(h) Cys/CySS is implicated in inflammation associated with various diseases.The purpose of the present study was to determine whether oxidized E(h) Cys/CySS is a determinant of interleukin (IL)-1beta levels. Results showed a 1.7-fold increase in secreted pro-IL-1beta levels in U937 monocytes exposed to oxidized E(h) Cys/CySS (-46 mV), compared to controls exposed to a physiological E(h) of -80 mV (P<0.01). In LPS-challenged mice, preservation of plasma E(h) Cys/CySS from oxidation by dietary sulfur amino acid (SAA) supplementation, was associated with a 1.6-fold decrease in plasma IL-1beta compared to control mice fed an isonitrogenous SAA-adequate diet (P<0.01). Analysis of E(h) Cys/CySS and IL-1beta in human plasma revealed a significant positive association between oxidized E(h) Cys/CySS and IL-1beta after controlling for age, gender, and BMI (P<0.001).These data show that oxidized extracellular E(h) Cys/CySS is a determinant of IL-1beta levels, and suggest that strategies to preserve E(h) Cys/CySS may represent a means to control IL-1beta in inflammatory disease states

Intracellular Transport of Plant Viruses: Finding the Door out of the Cell

Plant viruses are a class of plant pathogens that specialize in movement from cell to cell. As part of their arsenal for infection of plants, every virus encodes a movement protein (MP), a protein dedicated to enlarging the pore size of plasmodesmata (PD) and actively transporting the viral nucleic acid into the adjacent cell. As our knowledge of intercellular transport has increased, it has become apparent that viruses must also use an active mechanism to target the virus from their site of replication within the cell to the PD. Just as viruses are too large to fit through an unmodified plasmodesma, they are also too large to be freely diffused through the cytoplasm of the cell. Evidence has accumulated now for the involvement of other categories of viral proteins in intracellular movement in addition to the MP, including viral proteins originally associated with replication or gene expression. In this review, we will discuss the strategies that viruses use for intracellular movement from the replication site to the PD, in particular focusing on the role of host membranes for intracellular transport and the coordinated interactions between virus proteins within cells that are necessary for successful virus spread

Study of recanalization with MRI gradient-echo sequence and near-infrared spectroscopy during acute ischemic stroke

A la phase aigüe des accidents ischémiques cérébraux, l'objectif thérapeutique principal est l'obtention d'une recanalisation de l'artère occluse et d'une reperfusion de la zone de pénombre ischémique. L'identification de facteurs prédictifs d'une recanalisation et le développement de nouveaux outils de surveillance est d'un intérêt majeur lors de la mise en oeuvre de ces thérapeutiques. Dans la première partie de notre travail, nous avons étudié la valeur pronostique de la visibilité initiale du thrombus sur les séquences IRM en T2* et son évolution lors d'acquisitions séquentielles chez les patients traités par thrombolyse intraveineuse. Nous avons confirmé la valeur péjorative cette visibilité initiale, et souligné les discordances entre les données de l'angioIRM et de la séquence T2* lors de l'analyse séquentielle. Dans la seconde partie du travail, nous avons évalué l'intérêt de la spectroscopie de proche infrarouge comme méthode permettant d'évaluer le bénéfice de la recanalisation chez les patients traités par thrombectomie mécanique. Cette technologie semble intéressante, mais présente cependant des limites discutées dans ce travailAcute ischemic stroke treatments (intravenous thrombolysis, mechanical thrombectomy) aim to restore an affective brain perfusion in order to improve neurological outcome. We first evaluated the predictive value of susceptibility vessel sign (SVS) on T2* MRI sequence after intravenous thrombolysis and studied course of SVS using sequential MRI assessment. We confirm that SVS is a strong predictor of no recanalisation, and underline discrepancies between MR angiography and T2* data. In the second part, we assessed the usefulness of near-infrared spectroscopy (NIRS) to monitor recanalisation during mechanical thrombectomy. NIRS is a reliable tool, but still suffer of challenging limitation

Évaluation de la recanalisation au cours des accidents ischémiques cérébraux : intérêt de la séquence IRM en T2* et de la spectroscopie de proche infra-rouge

Acute ischemic stroke treatments (intravenous thrombolysis, mechanical thrombectomy) aim to restore an affective brain perfusion in order to improve neurological outcome. We first evaluated the predictive value of susceptibility vessel sign (SVS) on T2* MRI sequence after intravenous thrombolysis and studied course of SVS using sequential MRI assessment. We confirm that SVS is a strong predictor of no recanalisation, and underline discrepancies between MR angiography and T2* data. In the second part, we assessed the usefulness of near-infrared spectroscopy (NIRS) to monitor recanalisation during mechanical thrombectomy. NIRS is a reliable tool, but still suffer of challenging limitationsA la phase aigüe des accidents ischémiques cérébraux, l'objectif thérapeutique principal est l'obtention d'une recanalisation de l'artère occluse et d'une reperfusion de la zone de pénombre ischémique. L'identification de facteurs prédictifs d'une recanalisation et le développement de nouveaux outils de surveillance est d'un intérêt majeur lors de la mise en oeuvre de ces thérapeutiques. Dans la première partie de notre travail, nous avons étudié la valeur pronostique de la visibilité initiale du thrombus sur les séquences IRM en T2* et son évolution lors d'acquisitions séquentielles chez les patients traités par thrombolyse intraveineuse. Nous avons confirmé la valeur péjorative cette visibilité initiale, et souligné les discordances entre les données de l'angioIRM et de la séquence T2* lors de l'analyse séquentielle. Dans la seconde partie du travail, nous avons évalué l'intérêt de la spectroscopie de proche infrarouge comme méthode permettant d'évaluer le bénéfice de la recanalisation chez les patients traités par thrombectomie mécanique. Cette technologie semble intéressante, mais présente cependant des limites discutées dans ce travai

Dynamique du stress oxydatif et de l'excrétion de mélatonine à la phase aigüe des accidents ischémiques cérébraux

LYON1-BU Santé (693882101) / SudocSudocFranceF