Oligomeric behavior of the RND transporters CusA and AcrB in micellar solution of detergent

AbstractWe have used analytical ultracentrifugation to explore the oligomeric states of AcrB and CusA in micellar solution of detergent. These two proteins belong to the resistance, nodulation and cell division (RND) family of efflux proteins that are involved in multiple drug and heavy metal resistance. Only the structure of AcrB has been determined so far. Although functional RND proteins should assemble as trimers as AcrB does, both AcrB and CusA form a mixture of quaternary structures (from monomer to heavy oligomer) in detergent solution. The distribution of the oligomeric states was studied as a function of different parameters: nature and concentration of the detergent, ionic strength, pH, protein concentration. This pseudo-heterogeneity does not hamper the crystallization of AcrB as a homotrimer

In vitro production of cat-restricted Toxoplasma pre-sexual stages

Sexual reproduction of Toxoplasma gondii, confined to the felid gut, remains largely uncharted owing to ethical concerns regarding the use of cats as model organisms. Chromatin modifiers dictate the developmental fate of the parasite during its multistage life cycle, but their targeting to stage-specific cistromes is poorly described$^{1,2}$. Here we found that the transcription factors AP2XII-1 and AP2XI-2 operate during the tachyzoite stage, a hallmark of acute toxoplasmosis, to silence genes necessary for merozoites, a developmental stage critical for subsequent sexual commitment and transmission to the next host, including humans. Their conditional and simultaneous depletion leads to a marked change in the transcriptional program, promoting a full transition from tachyzoites to merozoites. These in vitro-cultured pre-gametes have unique protein markers and undergo typical asexual endopolygenic division cycles. In tachyzoites, AP2XII-1 and AP2XI-2 bind DNA as heterodimers at merozoite promoters and recruit MORC and HDAC3 (ref. $^{1}$), thereby limiting chromatin accessibility and transcription. Consequently, the commitment to merogony stems from a profound epigenetic rewiring orchestrated by AP2XII-1 and AP2XI-2. Successful production of merozoites in vitro paves the way for future studies on Toxoplasma sexual development without the need for cat infections and holds promise for the development of therapies to prevent parasite transmission

Chromatin modifications: implications in the regulation of gene expression in Toxoplasma gondii.

International audienceThe apicomplexan Toxoplasma gondii completes its life cycle by successive processes of parasite differentiation that rely on a tight control of gene expression to ensure appropriate protein profiles on time. During the last 5 years, several groups have pioneered this field of investigation, suggesting that epigenetics could play an important role in the control of parasite gene expression. Histone modifications serve as an effective way to regulate gene transcription but they do not operate alone; rather, they act in concert with other putative epigenetic information carriers (histone variants, small RNAs) and DNA sequence-specific transcription factors to modulate the higher-order structure of the chromatin fibre and govern the on-time recruitment of the transcriptional machinery to specific genes. Regarding the 'histone code' hypothesis, the parasite is endowed with a rich repertoire of histone-modifying enzymes catalysing site-selective modifications, which are subsequently interpreted by effector proteins that recognize specific covalent marks. Still, several peculiarities seem unique to T. gondii. This review is a synthesis of the current knowledge of how epigenetics contribute to the control of gene expression in T. gondii and, likely, other Apicomplexa

Ovine mononuclear phagocytes in situ: identification by monoclonal antibodies and involvement in experimental pyogranulomas

International audienceIn order to characterize in situ the macrophages present in experimental pyogranulomas induced in lambs with Corynebacterium pseudotuberculosis, a set of monoclonal antibodies (MAbs) was produced following immunization of BALB/c mice with alveolar macrophages from healthy sheep. Three MAbs were retained after two steps of screening using alveolar macrophages, peripheral blood lymphocytes, and polymorphonuclear leukocytes as target cells. Their reactivity was tested not only on macrophages in pyogranulomas but also on sections of various organs in steady-state conditions. One MAb, termed OM1, recognized the monocytes and the majority of cells of the mononuclear phagocyte system in lymphoid and nonlymphoid organs. The two other MAbs, OM2 and OM3, reacted with a subpopulation of alveolar macrophages and with other cell types in tissues, in particular with endothelial cells for the MAb OM2. On sections of experimental pyogranulomas that developed in lymph nodes draining the C. pseudotuberculosis-injected sites, MAb OM1 reacted with all the macrophages distributed in a palisade surrounding the necrotic center of the lesion from day 6 to day 28 postinoculation. The two other MAbs, OM2 and OM3, enabled two types of granulomas to be distinguished: one type was characterized by a large number of epithelioid cells stained by OM2; and the other was characterized by a few OM2-positive macrophages, whereas the OM3-positive cells were more numerous. These results show that macrophages are predominant cells in pyogranulomas and suggest two different histological patterns in the evolution of pyogranulomas induced by C. pseudotuberculosis, according to the immunological status of the host

Ovine mononuclear phagocytes in situ: identification by monoclonal antibodies and involvement in experimental pyogranulomas

International audienceIn order to characterize in situ the macrophages present in experimental pyogranulomas induced in lambs with Corynebacterium pseudotuberculosis, a set of monoclonal antibodies (MAbs) was produced following immunization of BALB/c mice with alveolar macrophages from healthy sheep. Three MAbs were retained after two steps of screening using alveolar macrophages, peripheral blood lymphocytes, and polymorphonuclear leukocytes as target cells. Their reactivity was tested not only on macrophages in pyogranulomas but also on sections of various organs in steady-state conditions. One MAb, termed OM1, recognized the monocytes and the majority of cells of the mononuclear phagocyte system in lymphoid and nonlymphoid organs. The two other MAbs, OM2 and OM3, reacted with a subpopulation of alveolar macrophages and with other cell types in tissues, in particular with endothelial cells for the MAb OM2. On sections of experimental pyogranulomas that developed in lymph nodes draining the C. pseudotuberculosis-injected sites, MAb OM1 reacted with all the macrophages distributed in a palisade surrounding the necrotic center of the lesion from day 6 to day 28 postinoculation. The two other MAbs, OM2 and OM3, enabled two types of granulomas to be distinguished: one type was characterized by a large number of epithelioid cells stained by OM2; and the other was characterized by a few OM2-positive macrophages, whereas the OM3-positive cells were more numerous. These results show that macrophages are predominant cells in pyogranulomas and suggest two different histological patterns in the evolution of pyogranulomas induced by C. pseudotuberculosis, according to the immunological status of the host

copH from Cupriavidus metallidurans CH34. A novel perplasmic copper-Binding Protein

International audienc

The small ubiquitin-like modifier (SUMO)-conjugating system of Toxoplasma gondii.

International audienceSUMOylation, the reversible covalent attachment of small ubiquitin-like modifier (SUMO) peptides has emerged as an important regulator of target protein function. Here we show, by characterization of the Toxoplasma gondii SUMO pathway, that the SUMO conjugation system operates in apicomplexan parasites. A gene encoding the SUMO tag was discovered as were genes encoding the various enzymes required for SUMO processing, ligation and release. Various SUMO conjugates were immuno-detected and by means of a global proteomic-based approach, we identified several T. gondii SUMOylated proteins that reveal many diverse cellular processes in which the modification plays a role. More specifically, SUMO conjugates were seen at the tachyzoite surface in response to signaling generated by host cell contact at the time of invasion. Also, under tissue culture conditions that stimulate bradyzoite differentiation (alkaline pH), we observed the conjugates at the parasitophorous vacuole membrane. The labeling was also at the surface of the mature cysts isolated from parasite-infected mouse brain. Overall, the SUMO conjugation system appears to be a complex and functionally heterogeneous pathway for protein modification in T. gondii with initial data indicating that it is likely to play a putative role in host cell invasion and cyst genesis

Poverty in the 1990s Evidence from the 1994 Living in Ireland survey

SIGLEAvailable from British Library Document Supply Centre-DSC:4111.1682(170) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

SET8-Mediated Methylations of Histone H4 Lysine 20 Mark Silent Heterochromatic Domains in Apicomplexan Genomes.

International audiencePost-translational histone modifications modulate chromatin-templated processes in various biological systems. H4K20 methylation is considered to have an evolutionary ancient role in DNA repair/genome integrity, while its function in heterochromatin function/gene expression is thought to have arisen later during evolution. Here, we identify and characterize H4K20 methylases of the Set8 family in Plasmodium and Toxoplasma, two medically-important members of the Apicomplexan phylum of protozoa. Remarkably, parasite Set8-related proteins display H4K20 mono-, di- and trimethylase activity in striking contrast with the mono-methylase restricted human Set8. Structurally, few residues forming the substrate-specific channel dictate the enzyme methylation multiplicity. These enzymes are cell cycle regulated and focally enriched at pericentric and telomeric heterochromatin in both parasites. Collectively, our findings provide new insights into the evolution of Set8-mediated biochemical pathways suggesting that the heterochromatic function of the mark is not restricted to metazoans. Thus, these lower eukaryotes have developed a diverse panel of biological stages through their high capacity to differentiate and epigenetics only begins to emerge as a strong determinant of their biology