Genome-wide localization of histone variants in Toxoplasma gondii implicates variant exchange in stage-specific gene expression.

BACKGROUND: Toxoplasma gondii is a protozoan parasite that differentiates from acute tachyzoite stages to latent bradyzoite forms in response to environmental cues that modify the epigenome. We studied the distribution of the histone variants CenH3, H3.3, H2A.X, H2A.Z and H2B.Z, by genome-wide chromatin immunoprecipitation to understand the role of variant histones in developmental transitions of T. gondii parasites. RESULTS: H3.3 and H2A.X were detected in telomere and telomere associated sequences, whereas H3.3, H2A.X and CenH3 were enriched in centromeres. Histones H2A.Z and H2B.Z colocalize with the transcriptional activation mark H3K4me3 in promoter regions surrounding the nucleosome-free region upstream of the transcription start site. The H2B.Z/H2A.Z histone pair also localizes to the gene bodies of genes that are silent but poised for activation, including bradyzoite stage-specific genes. The majority of H2A.X and H2A.Z/H2B.Z loci do not overlap, consistent with variant histones demarcating specific functional regions of chromatin. The extent of enrichment of H2A.Z/H2B.Z (and H3.3 and H2A.X) within the entire gene (5'UTR and gene body) reflects the timing of gene expression during the cell cycle, suggesting that dynamic turnover of H2B.Z/H2A.Z occurs during the tachyzoite cell cycle. Thus, the distribution of the variant histone H2A.Z/H2B.Z dimer defines active and developmentally silenced regions of the T. gondii epigenome including genes that are poised for expression. CONCLUSIONS: Histone variants mark functional regions of parasite genomes with the dynamic placement of the H2A.Z/H2B.Z dimer implicated as an evolutionarily conserved regulator of parasite and eukaryotic differentiation

Essential role of Plasmodium perforin-like protein 4 in ookinete midgut passage.

Pore forming proteins such as those belonging to the membrane attack/perforin (MACPF) family have important functions in many organisms. Of the five MACPF proteins found in Plasmodium parasites, three have functions in cell passage and one in host cell egress. Here we report an analysis of the perforin-like protein 4, PPLP4, in the rodent parasite Plasmodium berghei. We found that the protein is expressed only in the ookinete, the invasive stage of the parasite formed in the mosquito midgut. Transcriptional analysis revealed that expression of the pplp4 gene commences during ookinete development. The protein was detected in retorts and mature ookinetes. Using two antibodies, the protein was found localized in a dotted pattern, and 3-D SIM super-resolution microcopy revealed the protein in the periphery of the cell. Analysis of a C-terminal mCherry fusion of the protein however showed mainly cytoplasmic label. A pplp4 null mutant formed motile ookinetes, but these were unable to invade and traverse the midgut epithelium resulting in severely impaired oocyst formation and no transmission to naïve mice. However, when in vitro cultured ookinetes were injected into the thorax of the mosquito, thus by-passing midgut passage, sporozoites were formed and the mutant parasites were able to infect naïve mice. Taken together, our data show that PPLP4 is required only for ookinete invasion of the mosquito midgut. Thus PPLP4 has a similar role to the previously studied PPLP3 and PPLP5, raising the question why three proteins with MACPF domains are needed for invasion by the ookinete of the mosquito midgut epithelium

Molecular epidemiology and expression of capsular polysaccharides in Staphylococcus aureus clinical isolates in the United States.

Staphylococcus aureus capsular polysaccharides (CP) are important virulence factors under evaluation as vaccine antigens. Clinical S. aureus isolates have the biosynthetic capability to express either CP5 or CP8 and an understanding of the relationship between CP genotype/phenotype and S. aureus epidemiology is valuable. Using whole genome sequencing, the clonal relatedness and CP genotype were evaluated for disease-associated S. aureus isolates selected from the Tigecycline Evaluation and Surveillance Trial (T.E.S.T) to represent different geographic regions in the United States (US) during 2004 and 2009-10. Thirteen prominent clonal complexes (CC) were identified, with CC5, 8, 30 and 45 representing >80% of disease isolates. CC5 and CC8 isolates were CP type 5 and, CC30 and CC45 isolates were CP type 8. Representative isolates from prevalent CC were susceptible to in vitro opsonophagocytic killing elicited by anti-CP antibodies, demonstrating that susceptibility to opsonic killing is not linked to the genetic lineage. However, as not all S. aureus isolates may express CP, isolates representing the diversity of disease isolates were assessed for CP production. While approximately 35% of isolates (primarily CC8) did not express CP in vitro, CP expression could be clearly demonstrated in vivo for 77% of a subset of these isolates (n = 20) despite the presence of mutations within the capsule operon. CP expression in vivo was also confirmed indirectly by measuring an increase in CP specific antibodies in mice infected with CP5 or CP8 isolates. Detection of antigen expression in vivo in relevant disease states is important to support the inclusion of these antigens in vaccines. Our findings confirm the validity of CP as vaccine targets and the potential of CP-based vaccines to contribute to S. aureus disease prevention

Relation of carbohydrate reserves with the forthcoming crop, flower formation and photosynthetic rate, in the alternate bearing Salustiana sweet orange (Citrus sinensis L.)

[EN] The aim of this work was to assess the relation between carbohydrate levels and flower and fruit production, as well as the role of carbohydrates on CO(2) fixation activity, by analysis of leaves, twigs and roots from the alternate bearing 'Salustiana' cultivar of sweet orange (Citrus sinensis [L.] Osbeck). A heavy crop load (on year) did not affect photosynthesis activity when compared to non-fruiting trees (off year). Fruiting trees accumulated most of the fixed carbon in mature fruits, whilst no accumulation was observed in roots before harvest. Non-fruiting trees transported part of the fixed carbon to the roots and mobilize it for growth processes and, at the end of the season (December), store it as reserves. Reserve carbohydrates accumulation in leaves started by early December for both tree types, showing the same levels in on and off trees until spring bud sprouting. A heavy flowering after an off year caused the rapid mobilization of the stored reserves, which were exhausted at full bloom. We found no evidence on carbon fixation regulation by either fruit demand or carbohydrate levels in leaves. Carbohydrate reserves played little or no role over fruit set, which actually relied on current photosynthesisWe thank Ing. Agr. J.M. Torres (ANECOOP, Valencia, Spain) for providing the orchard facilities and logistic help, the R + D + i Linguistic Assistance Office at the Universidad Politecnica de Valencia for their help in revising this article and Y. Bordon for her cooperation in some experiments. Thanks are due also to Dr. Olivares for the critical review of the manuscript. This research was funded by grants from the Conselleria de Agricultura, Pesca y Alimentacion (GV-CAPA00-11) and the Conselleria diEmpresa, Universitat i Ciencia, Generalitat Valenciana (Grupos 04/059).Monerri Huguet, MC.; Fortunato De Almeida, A.; Molina Romero, RV.; González Nebauer, S.; García Luís, MD.; Guardiola Barcena, JL. (2011). Relation of carbohydrate reserves with the forthcoming crop, flower formation and photosynthetic rate, in the alternate bearing Salustiana sweet orange (Citrus sinensis L.). Scientia Horticulturae. 129(1):71-78. https://doi.org/10.1016/j.scienta.2011.03.009S7178129

Molecular determinants of binding to the Plasmodium subtilisin-like protease 1.

PfSUB1, a subtilisin-like protease of the human malaria parasite Plasmodium falciparum, is known to play important roles during the life cycle of the parasite and has emerged as a promising antimalarial drug target. In order to provide a detailed understanding of the origin of binding determinants of PfSUB1 substrates, we performed molecular dynamics simulations in combination with MM-GBSA free energy calculations using a homology model of PfSUB1 in complex with different substrate peptides. Key interactions, as well as residues that potentially make a major contribution to the binding free energy, are identified at the prime and nonprime side of the scissile bond and comprise peptide residues P4 to P2'. This finding stresses the requirement for peptide substrates to interact with both prime and nonprime side residues of the PfSUB1 binding site. Analyzing the energetic contributions of individual amino acids within the peptide-PfSUB1 complexes indicated that van der Waals interactions and the nonpolar part of solvation energy dictate the binding strength of the peptides and that the most favorable interactions are formed by peptide residues P4 and P1. Hot spot residues identified in PfSUB1 are dispersed over the entire binding site, but clustered areas of hot spots also exist and suggest that either the S4-S2 or the S1-S2' binding site should be exploited in efforts to design small molecule inhibitors. The results are discussed with respect to which binding determinants are specific to PfSUB1 and, therefore, might allow binding selectivity to be obtained

P113 is a merozoite surface protein that binds the N terminus of Plasmodium falciparum RH5.

Invasion of erythrocytes by Plasmodium falciparum merozoites is necessary for malaria pathogenesis and is therefore a primary target for vaccine development. RH5 is a leading subunit vaccine candidate because anti-RH5 antibodies inhibit parasite growth and the interaction with its erythrocyte receptor basigin is essential for invasion. RH5 is secreted, complexes with other parasite proteins including CyRPA and RIPR, and contains a conserved N-terminal region (RH5Nt) of unknown function that is cleaved from the native protein. Here, we identify P113 as a merozoite surface protein that directly interacts with RH5Nt. Using recombinant proteins and a sensitive protein interaction assay, we establish the binding interdependencies of all the other known RH5 complex components and conclude that the RH5Nt-P113 interaction provides a releasable mechanism for anchoring RH5 to the merozoite surface. We exploit these findings to design a chemically synthesized peptide corresponding to RH5Nt, which could contribute to a cost-effective malaria vaccine

Juxtamembrane Shedding of Plasmodium falciparum AMA1 Is Sequence Independent and Essential, and Helps Evade Invasion-Inhibitory Antibodies

The malarial life cycle involves repeated rounds of intraerythrocytic replication interspersed by host cell rupture which releases merozoites that rapidly invade fresh erythrocytes. Apical membrane antigen-1 (AMA1) is a merozoite protein that plays a critical role in invasion. Antibodies against AMA1 prevent invasion and can protect against malaria in vivo, so AMA1 is of interest as a malaria vaccine candidate. AMA1 is efficiently shed from the invading parasite surface, predominantly through juxtamembrane cleavage by a membrane-bound protease called SUB2, but also by limited intramembrane cleavage. We have investigated the structural requirements for shedding of Plasmodium falciparum AMA1 (PfAMA1), and the consequences of its inhibition. Mutagenesis of the intramembrane cleavage site by targeted homologous recombination abolished intramembrane cleavage with no effect on parasite viability in vitro. Examination of PfSUB2-mediated shedding of episomally-expressed PfAMA1 revealed that the position of cleavage is determined primarily by its distance from the parasite membrane. Certain mutations at the PfSUB2 cleavage site block shedding, and parasites expressing these non-cleavable forms of PfAMA1 on a background of expression of the wild type gene invade and replicate normally in vitro. The non-cleavable PfAMA1 is also functional in invasion. However – in contrast to the intramembrane cleavage site - mutations that block PfSUB2-mediated shedding could not be stably introduced into the genomic pfama1 locus, indicating that some shedding of PfAMA1 by PfSUB2 is essential. Remarkably, parasites expressing shedding-resistant forms of PfAMA1 exhibit enhanced sensitivity to antibody-mediated inhibition of invasion. Drugs that inhibit PfSUB2 activity should block parasite replication and may also enhance the efficacy of vaccines based on AMA1 and other merozoite surface proteins

A protease cascade regulates release of the human malaria parasite Plasmodium falciparum from host red blood cells

Malaria parasites replicate within a parasitophorous vacuole in red blood cells (RBCs). Progeny merozoites egress upon rupture of first the parasitophorous vacuole membrane (PVM), then poration and rupture of the RBC membrane (RBCM). Egress is protease-dependent1, but none of the effector molecules that mediate membrane rupture have been identified and it is unknown how sequential rupture of the two membranes is controlled. Minutes before egress, the parasite serine protease SUB1 is discharged into the parasitophorous vacuole2,3,4,5,6 where it cleaves multiple substrates2,5,7,8,9 including SERA6, a putative cysteine protease10,11,12. Here, we show that Plasmodium falciparum parasites lacking SUB1 undergo none of the morphological transformations that precede egress and fail to rupture the PVM. In contrast, PVM rupture and RBCM poration occur normally in SERA6-null parasites but RBCM rupture does not occur. Complementation studies show that SERA6 is an enzyme that requires processing by SUB1 to function. RBCM rupture is associated with SERA6-dependent proteolytic cleavage within the actin-binding domain of the major RBC cytoskeletal protein β-spectrin. We conclude that SUB1 and SERA6 play distinct, essential roles in a coordinated proteolytic cascade that enables sequential rupture of the two bounding membranes and culminates in RBCM disruption through rapid, precise, SERA6-mediated disassembly of the RBC cytoskeleton

Alterações nas reservas de sementes de Dalbergia nigra ((Vell.) Fr. All. ex Benth.) durante a hidratação

Seed imbibitions is the first stage of the germination process and is characterized by the hydration of tissues and cells and the activation and/or induction of the enzymes responsible for mobilizing reserves for respiration and the construction of new cell structures. The objective of this study was to investigate the alterations in reserve substances during slow hydration of Bahia Rosewood (Dalbergia nigra) seeds in water. Seeds from two different lots (Lot I and II) were placed in saturated desiccators (95-99% RH) to hydrate at 15 and 25 °C until water contents of 10, 15, 20 and 25% were reached. At each level of hydration, changes in lipid reserves, soluble carbohydrates, starch and soluble proteins were evaluated. The mobilization of reserves was similarly assessed in both lots, with no differences being observed between the two hydration temperatures. Lipid contents showed little variation during hydration, while the contents of soluble carbohydrates and starch decreased after the 15% water content level. Soluble proteins showed a gradual tendency to decrease between the control (dry seeds) up to 25% water content

Microbiome to Brain:Unravelling the Multidirectional Axes of Communication

The gut microbiome plays a crucial role in host physiology. Disruption of its community structure and function can have wide-ranging effects making it critical to understand exactly how the interactive dialogue between the host and its microbiota is regulated to maintain homeostasis. An array of multidirectional signalling molecules is clearly involved in the host-microbiome communication. This interactive signalling not only impacts the gastrointestinal tract, where the majority of microbiota resides, but also extends to affect other host systems including the brain and liver as well as the microbiome itself. Understanding the mechanistic principles of this inter-kingdom signalling is fundamental to unravelling how our supraorganism function to maintain wellbeing, subsequently opening up new avenues for microbiome manipulation to favour desirable mental health outcome