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Macins are a distinct class of antimicrobial peptides (AMPs) produced by leeches and Hydra. Their function depends strongly on their three-dimensional structure. In order to support structural elucidation of these AMPs, the knowledge and proper assignment of disulfide bonds formed in these cysteine-rich peptides is a prerequisite. In this report, we outline an analytical strategy, encompassing a combination of top-down MS based analytics and sequence-dependent enzyme cleavage under native conditions followed by high mass accuracy and high resolution MS/MS analysis by LTQ-Orbitrap MS to assign disulfide linkages of three members of the macin family, namely neuromacin, theromacin, and hydramacin-1. The results revealed that the eight cysteine residues conserved in all three macins form the same four disulfide bonds, i.e. [C1:C6], [C2:C5], [C3:C7], and [C4:C8]. Theromacin, which possess two additional cysteine residues, forms a fifth disulfide bond. Biological significance Beside the high biological significance which is based on the inherent dependence of biological activity on the structural features of antimicrobial peptides (which holds true for entirely every protein), the presented analytical strategy will be of wide interest, as it widens the available toolbox for the analysis of this important posttranslational modification.

The erythrocytic life cycle of Plasmodium falciparum is highly associated with severe clinical symptoms of malaria that causes hundreds of thousands of death each year. The parasite develops within human erythrocytes leading to the disruption of the infected red blood cell (iRBC) prior to the start of a new cycle of erythrocyte infection. Emerging mechanisms of resistance against antimalarial drugs require improved knowledge about parasite's blood stages to facilitate new alternative antimalarial strategies. For the analysis of young blood stages of Plasmodium at the molecular level, the isolation of ring stages is essential. However, early stages can hardly be separated from both, late stages and non-infected red blood cells using conventional methods. Here, iRBCs were stained with the DNA-binding dyes Vybrant® DyeCycle™ Violet and SYBR® Green I. Subsequently, cells were subjected to flow-cytometric analysis. This enabled the discrimination of early stage iRBCs as well as late-stage iRBCs from non-infected erythrocytes and the properties of the used dyes were evaluated. Moreover, early stage iRBCs were isolated with high purity (>98%) by FACS. Subsequently, development of sorted early stages of the parasite was monitored over time and compared with control cultures. The described flow cytometry method, based on staining with Vybrant DyeCycle Violet, allows the isolation of viable ring stages of the malarial agent P. falciparum, and thereby provides the basis for new, broad-range molecular investigations of the parasite. © 2012 International Society for Advancement of Cytometry

International audience; The tertiary structures of theromacin and neuromacin confirmed the macin protein family as a self-contained family of antimicrobial proteins within the superfamily of scorpion toxin-like proteins. The macins, which also comprise hydramacin-1, are antimicrobially active against Gram-positive and Gram-negative bacteria. Despite high sequence identity, the three proteins showed distinct differences with respect to their biological activity. Neuromacin exhibited a significantly stronger capacity to permeabilize the cytoplasmic membrane of Bacillus megaterium than theromacin and hydramacin-1. Accordingly, it is the only macin that displays pore-forming activity and that was potently active against Staphylococcus aureus. Moreover, neuromacin and hydramacin-1 led to an aggregation of bacterial cells that was not observed with theromacin. Analysis of the molecular surface properties of macins allowed confirmation of the barnacle model as the mechanistic model for the aggregation effect. Besides being antimicrobially active, neuromacin and theromacin, in contrast to hydramacin-1, were able to enhance the repair of leech nerves ex vivo. Notably, all three macins enhanced the viability of murine neuroblastoma cells, extending their functional characteristics. As neuromacin appears to be both a functional and structural chimera of hydramacin-1 and theromacin, the putative structural correlate responsible for the nerve repair capacity in leech was located to a cluster of six amino acid residues using the sequence similarity of surface-exposed regions.

Cytotoxic T cells mobilize effector proteins from prestored lysosomal compartments. Since different activation signals result in alternative routes of target cell killing, utilizing either FasL or the granzyme B/perforin pathway, the existence of distinct forms of effector granules was recently suggested. Applying a protocol for the separation of intact organelles from activated T lymphoblasts, we noticed that FasL-associated secretory lysosomes (SL) segregate from vesicles containing larger amounts of granzymes and granulysin. We previously analyzed the proteome of secretory lysosomes from NK and T cells and now describe the proteome of granzyme-containing vesicles. Moreover, intact FasL-associated SL and granzyme-containing vesicles were compared by electron microscopy and respective extracts were characterized by Western blotting. With the present report, we provide a comprehensive proteome map of granzyme-containing granules and unequivocally demonstrate that T lymphoblasts contain at least two distinct types of effector vesicles. Moreover, the overall protein content of the two vesicle populations was compared by 2D difference gel electrophoresis. Interestingly, the observed differences in protein distribution were not restricted to effector proteins but also applied to cytoskeleton-associated elements that could argue for a differential transport or initiation of degranulation. To our knowledge, this is the first comprehensive description of distinct effector granules in T cells.

Despite partial sequence identity and structural similarity, human β-defensin 3 (HBD3) kills Staphylococcus aureus with a 4- to 8-fold higher efficiency than human β-defensin 2 (HBD2), whereas the activities against Escherichia coli are identical. The design and characterization of HBD2/HBD3 chimeric peptides revealed that distinct molecular regions are responsible for their divergent killing properties. Two of the chimeras killed both E. coli and S. aureus with an even higher efficacy than the wild-type molecules. Moreover, one of these two chimeras maintained its high killing activities in the presence of physiologic salt concentrations. Due to the broad spectrum of their antimicrobial activities against many human multidrug-resistant pathogens, these two designer peptides of human origin represent promising templates for a new class of antibiotics.

The allergen content of standardized pollen material is crucial for an effective diagnosis and treatment. However, variations in IgE reactivities of allergic patients to different preparations of Phleum pratense pollen have been reported. In order to define and directly compare the allergen composition of pollen preparations provided by different suppliers, a comprehensive proteome analysis of three different timothy grass pollen extracts was performed. More than 140 proteins were annotated comprising the pollen proteome/allergome in a global 2-D map. With regard to the individual pollen preparations, several major differences in the overall protein composition were detected that also affected known Phleum allergens and their isoforms. Importantly, these differences were also reflected at the level of antibody reactivities in 1-D and 2-D immunoblots. As a consequence, it is suggested that the observed differences should be taken into consideration aiming for a standardized diagnosis and therapy of grass pollen allergies as recommended by international medical agencies.

Early embryos of many organisms develop outside the mother and are immediately confronted with myriads of potential colonizers. How these naive developmental stages control and shape the bacterial colonization is largely unknown. Here we show that early embryonic stages of the basal metazoan Hydra are able to control bacterial colonization by using maternal antimicrobial peptides. Antimicrobial peptides of the periculin family selecting for a specific bacterial colonization during embryogenesis are produced in the oocyte and in early embryos. If overexpressed in hydra ectodermal epithelial cells, periculin1a drastically reduces the bacterial load, indicating potent antimicrobial activity. Unexpectedly, transgenic polyps also revealed that periculin, in addition to bactericidal activity, changes the structure of the bacterial community. These findings delineate a role for antimicrobial peptides both in selecting particular bacterial partners during development and as important components of a “be prepared” strategy providing transgenerational protection.

Herein we report the synthesis of a series of novel constrained peptidomimetics 2-10 endowed with a dipeptide backbone (D-Ser-Gly) and a vinyl ester warhead, structurally related to a previously identified lead compound 1, an irreversible inhibitor of falcipain-2, the main haemoglobinase of lethal malaria parasite Plasmodium falciparum. The new compounds were evaluated for their inhibition against falcipain-2, as well as against cultured P. falciparum. The inhibitory activity of the synthesized compounds was also evaluated against another protozoal cysteine protease, namely rhodesain of Trypanosoma brucei rhodesiense.

This paper describes the synthesis of novel peptidomimetics bearing a protected aspartyl aldeyde warhead leading to the thioacylals 2a,b and the acylals 3a,b. Compounds 2a and 3a proved to possess an increased antiplasmodial activity with respect to the parent molecule 1. Furthermore thioacylal 2a can be considered as a promising trypanocidal agent.

New peptidic Michael acceptor based cysteine protease inhibitors displaying antiparasitic activity were identified by testing a broad series of 45 compounds in total, containing Asn, Gln, or Phe. As target enzymes, falcipain-2 and -3 from P. falciparum and rhodesain from T. b. rhodesiense were used. In the case of the Asn/Gln containing compounds, the trityl-protected, diastereomeric E-configured vinylogous dipeptide esters 16 (Boc-(S)-Phg-(R/S)-vGln(Trt)-OEt) were discovered as most active inhibitors concerning both protease inhibition and antiparasitic acitivity, with inhibition constants in the submicromolar range. The compounds were shown to display time-dependent and competitive inhibition. In the case of the Phe containing compounds, the maleic acid derivatives 42 and 43 (BnO-Phe--Mal-Phe-OBn, BnO-Phe--Mal-Phe-Ala-OBn, Mal = maleic acid) displayed good inhibition of rhodesain as well as good antitrypanosomal activity, while the fumaric acid derived E-analogue 14 (BnO-Phe--Fum-Phe-OBn) only displayed inhibition of the target enzymes but no antiparasitic activity. Inhibition by these Phe derivatives was shown to be time-independent and competitive.

Amoebapore A is a pore-forming protein produced by the pathogenic parasite Entamoeba histolytica , which causes human amoebic dysentery. The pore-forming activity of amoebapore A is regulated by pH-dependent dimerization, a prerequisite for membrane insertion and pore formation. Understanding of these important processes has been hampered by the cytotoxicity of amoebapore A, which prevents the production of this protein in cell-based expression systems. In this study, a protocol for the cell-free production of active recombinant amoebapore A is presented. Protein yields of ∼500 μg/ml of cell-free reaction were achieved. Recombinant amoebapore A was purified using a three-step procedure. To facilitate the structural characterization of the dimeric and pore forms, we adapted the cell-free system to isotope label amoebapore A for NMR studies. The preliminary assignment of a 2D 1 H– 15 N HSQC spectrum of a uniformly 13 C/ 15 N-labeled sample was achieved using a combinatorial selective 15 N-labeling approach coupled with available 1 H N chemical shift data, resulting in the unambiguous assignment of resonances from 55 of the 77 residues. To confirm these results and obtain the full sequence-specific assignments of the 2D 1 H– 15 N HSQC spectrum, a 3D HNCA spectrum was recorded. These assignment data will be used to aid the characterization of amoebapore A dimer formation and membrane insertion.

A series of 1-aryl-6,7-disubstituted-2H-isoquinolin-3-ones (2-10) was synthesized and evaluated for their inhibition against Plasmodium falciparum cysteine protease falcipain-2, as well as against cultured P. falciparum strain FCBR parasites. All compounds displayed inhibitory activity against recombinant falcipain-2 and against in vitro cultured intraerythrocytic P. falciparum, with the exception of 9. The new compounds exhibited no selectivity against human cysteine proteases such as cathepsins B and L. The inhibitory activity of the synthesized compounds was also evaluated against another protozoal cysteine protease, namely rhodesain of Trypanosoma brucei rhodesiense.

Entamoeba histolytica is known for its extraordinary capacity to destroy human tissues, leading to invasive diseases such as ulcerative colitis or extra-intestinal abscesses. In order to identify the virulence factors of this parasite phenotypes and proteomes of two recently identified genetically related cell lines (A and B), derived from the laboratory E. histolytica isolate HM-1:IMSS, were compared. Both cell lines are indistinguishable on the basis of highly polymorphic tandem repeat DNA sequences. However, cell line A is incapable to induce liver abscesses in experimentally infected rodents, whereas cell line B provokes considerable abscesses. Phenotypic analyses revealed increased hemolytic activity, lower growth rate, smaller cell size, reduced cysteine peptidase activity and lower resistance to nitric oxide stress for cell line A. In contrast, no differences between the two cell lines were found for cytopathic activity, erythrophagocytosis, digestion of erythrocytes or resistance to complement, hydrogen peroxide and superoxide radical anions. Proteomic comparison by 2-D DIGE followed by MS, identified a total of 21 proteins with higher abundance in cell line A and ten proteins with higher abundance in cell line B. Remarkably, three differentially up-regulated antioxidants were exclusively found in the pathogenic cell line B. Notably, only for two differentially regulated proteins, namely a Fe-hydrogenase and a C2 domain protein, a similar type was found at the level of transcription. Summarized, a defined set of different proteins could be identified between cell lines A and B. These molecules may have an important role in amoeba pathogenicity.

Defensins are small effector molecules of the innate immune system, synthesised by various organisms including plants and animals. The peptides act as endogenous antibiotics with an antimicrobial activity against a broad spectrum of microbes including bacteria, fungi and viruses. alpha-Defensins are a subgroup of the defensin family, their synthesis is limited to some tissues and furthermore to some mammalian species including the horse. Equine DEFA1 is an enteric alpha-defensin exclusively produced in Paneth cells. The peptide showed an activity against a broad spectrum of microbes, but typical pathogens of the horse were not included in the previous antimicrobial studies. Here, we report the antibacterial properties of DEFA1 against clinical isolates of typical horse pathogens including Rhodococcus equi, various streptococci strains, Salmonella choleraesuis, and Pasteurella multocida. The recombinantly expressed DEFA1 peptide exerted potent activity against these pathogenic bacteria. The highest susceptibility showed R. equi. Three genetically different strains of R. equi were killed at low micromolar concentrations, comparable with conventionally used antibiotics.

Pombe Cdc15 homology (PCH) family proteins are regarded as key elements for linking membrane-associated processes to cytoskeletal elements and thus play a major role in exo- and endocytosis and organelle trafficking. We previously reported that, via their SH3 domains, several members of the PCH proteins interact with the proline-rich region of Fas ligand (FasL, CD95L), a key death factor in immune cells. Since protein-protein interactions that govern the storage and transport of FasL-associated vesicles are largely unknown, the present study was performed to identify other potential binding partners for SH3 domains of FasL-interacting PCH proteins. To this end, individual SH3 domains were expressed as GST fusion proteins and used to precipitate associated proteins from leukemic T cell lines and activated human T cell blasts. 87 protein bands representing 34 individual proteins were identified by mass spectrometry. The presented list of candidate interactors not only highlights the role of PCH proteins as adapters between vesicular membranes and the cytoskeleton but also points to an involvement of these proteins in the regulation of signalling events in T lymphocytes.

Defensins are a predominant class of antimicrobial peptides, which act as endogenous antibiotics. Defensins are classified into three distinct sub-families: theta-, beta-, and alpha-defensins. Synthesis of alpha-defensin has been confirmed only in primates and glires to date and is presumably unique for a few tissues, including neutrophils and Paneth cells of the small intestine. Antimicrobial activities of these peptides were shown against a wide variety of microbes including bacteria, fungi, viruses and protozoan parasites. In the present study, we report the characterization of the equine alpha-defensin DEFA (defensin alpha) 1. Transcription analysis revealed that the transcript of the gene is present in the small intestine only. An alignment with known alpha-defensins from primates and glires displayed a homology with Paneth-cell-specific alpha-defensins. DEFA1 was recombinantly expressed in Escherichia coli and subsequently analysed structurally by CD and molecular modelling. To examine the antimicrobial properties, a radial diffusion assay was performed with 12 different micro-organisms and the LD90 (lethal dose killing > or =90% of target organism) and MBC (minimal bactericidal concentration) values were examined. DEFA1 showed an antimicrobial activity against different Gram-positive and Gram-negative bacteria and against the yeast Candida albicans. Using viable bacteria in combination with a membrane-impermeable fluorescent dye, as well as depolarization of liposomes as a minimalistic system, it became evident that membrane permeabilization is at least an essential part of the peptide's mode of action.

A broad protease-based and cell-based screening of protease inhibitors yielded the aziridine-2-carboxylic acid derivative 2 a and the N-acylated aziridine-2,3-dicarboxylic acid derivatives 32 a and 34 b as the most potent inhibitors of falcipain-2 and falcipain-3 (IC(50) falcipain-2: 0.079-5.4 microM, falcipain-3: 0.25-39.8 microM). As the compounds also display in vitro activity against the P. falciparum parasite in the submicromolar and low micromolar range, these compound classes are leads for new antiplasmodial falcipain inhibitors.

Mutations in the KCNQ2 gene cause myokymia and neonatal epilepsy, indicating that this K+ channel regulates the excitability of lower motoneurons and CNS neurons. Little is known about the parameters that direct the assembly of this multimeric molecule and other KCNQ subunits. Here, we show that the carboxy-terminal subunit interaction domain of KCNQ2 autonomously folds and assembles into tetramers. This domain contains a bipartite coiled-coil motif. Whereas structural integrity of the second coiled-coil motif is crucial for tetramer formation, that of the first motif is less important. These data suggest a crucial role of coiled-coil motifs in tetrameric KCNQ channel assembly.

Since completion of genome sequencing of the malarial parasite Plasmodium falciparum, proteomic tools for the identification of parasite proteins have become particularly attractive as they allow a more thorough interpretation of these data. Recent advances in 2-D PAGE, MS, and bioinformatics have created great opportunities for mapping and characterization of protein populations. We employed these improvements in a proteomic approach for the analysis of proteins detected in two blood stages of P. falciparum, (i) in the schizont stage and (ii) in the merozoite stage. For the isolation of merozoites, we introduced a new protocol based on the preparation of clustered structures of merozoites upon treatment of cultures with the common cysteine proteinase inhibitor E64. Peptide mass fingerprints of excised and trypsinated protein spots, acquired by MALDI-TOF MS were generated to identify a variety of proteins. Moreover, prefractionation procedures were used to enrich and map low-abundance proteins in protein samples. The data demonstrate that classic proteomic analyses using 2-D PAGE are now feasible for P. falciparum and represent the first step in the direction of creating 2-D reference maps for this medically most relevant protozoon.

In order to proceed through their life cycle, protozoan parasites of the genus Leishmania cycle between sandflies and mammals. This change of environment correlates with the differentiation from the promastigote stage (insect form) to the amastigote stage (intracellular mammalian form). The molecular basis underlying this major transformation is poorly understood so far; however, heat shock protein 90 (HSP90) appears to play a pivotal role. To further elucidate this process we identified proteins expressed preferentially in either of the two life cycle stages. By using two-dimensional (2-D) gel electrophoresis we observed defined changes in the protein pattern. A total of approximately 2000 protein spots were visualized. Of these, 31 proteins were present only in promastigotes. The abundance of 65 proteins increased during heat-induced in vitro amastigote differentiation, while a decreased abundance is observed for four proteins late in amastigote differentiation. Further analyses using matrix-assisted laser desorption/ionization-time of flight mass spectrometry and peptide mass fingerprinting 67 protein spots were identified representing 41 different proteins known from databases and eight hypothetical proteins. Further studies showed that most of the stage-specific proteins fall into five groups of functionally related proteins. These functional categories are: (i) stress response (e.g. heat, oxidative stress); (ii) cytoskeleton and cell membrane; (iii) energy metabolism and phosphorylation; (iv) cell cycle and proliferation; and (v) amino acid metabolism. Very similar changes in the 2-D protein pattern were obtained when in vitro amastigote differentiation was induced either by pharmacological inhibition of HSP90 or by a combination of heat stress and acidic pH supporting the critical role for HSP90 in life cycle control.

International audience; The emblematic hydrothermal worm Alvinella pompejana is one of the most thermo tolerant animal known on Earth. It relies on a symbiotic association offering a unique opportunity to discover biochemical adaptations that allow animals to thrive in such a hostile habitat. Here, by studying the Pompeii worm, we report on the discovery of the first antibiotic peptide from a deep-sea organism, namely alvinellacin. After purification and peptide sequencing, both the gene and the peptide tertiary structures were elucidated. As epibionts are not cultivated so far and because of lethal decompression effects upon Alvinella sampling, we developed shipboard biological assays to demonstrate that in addition to act in the first line of defense against microbial invasion, alvinellacin shapes and controls the worm's epibiotic microflora. Our results provide insights into the nature of an abyssal antimicrobial peptide (AMP) and into the manner in which an extremophile eukaryote uses it to interact with the particular microbial community of the hydrothermal vent ecosystem. Unlike earlier studies done on hydrothermal vents that all focused on the microbial side of the symbiosis, our work gives a view of this interaction from the host side.

A range of various assays to measure chemosusceptibility of Plasmodium falciparum have been described in the literature. As the screening of a plethora of compounds for antiplasmodial activity is urgently needed and becomes a constantly increasing routine analysis, a test system has to fulfill the following requirements: sensitivity, reliability, simplicity of performance, high-throughput compatibility, and cost-effectiveness. Here, we describe an assay that fulfills all criteria and in which the fluorescent SYTOX® Green dye is introduced to determine growth inhibition of Plasmodia in in vitro cultures.

Background & Aims Tumor necrosis factor-related apoptosis inducing ligand (TRAIL-R1) (TNFRSF10A) and TRAIL-R2 (TNFRSF10B) on the plasma membrane bind ligands that activate apoptotic and other signaling pathways. Cancer cells also might have TRAIL-R2 in the cytoplasm or nucleus, although little is known about its activities in these locations. We investigated the functions of nuclear TRAIL-R2 in cancer cell lines. Methods Proteins that interact with TRAIL-R2 initially were identified in pancreatic cancer cells by immunoprecipitation, mass spectrometry, and immunofluorescence analyses. Findings were validated in colon, renal, lung, and breast cancer cells. Functions of TRAIL-R2 were determined from small interfering RNA knockdown, real-time polymerase chain reaction, Drosha-activity, microRNA array, proliferation, differentiation, and immunoblot experiments. We assessed the effects of TRAIL-R2 overexpression or knockdown in human pancreatic ductal adenocarcinoma (PDAC) cells and their ability to form tumors in mice. We also analyzed levels of TRAIL-R2 in sections of PDACs and non-neoplastic peritumoral ducts from patients. Results TRAIL-R2 was found to interact with the core microprocessor components Drosha and DGCR8 and the associated regulatory proteins p68, hnRNPA1, NF45, and NF90 in nuclei of PDAC and other tumor cells. Knockdown of TRAIL-R2 increased Drosha-mediated processing of the let-7 microRNA precursor primary let-7 (resulting in increased levels of mature let-7), reduced levels of the let-7 targets (LIN28B and HMGA2), and inhibited cell proliferation. PDAC tissues from patients had higher levels of nuclear TRAIL-R2 than non-neoplastic pancreatic tissue, which correlated with increased nuclear levels of HMGA2 and poor outcomes. Knockdown of TRAIL-R2 in PDAC cells slowed their growth as orthotopic tumors in mice. Reduced nuclear levels of TRAIL-R2 in cultured pancreatic epithelial cells promoted their differentiation. Conclusions Nuclear TRAIL-R2 inhibits maturation of the microRNA let-7 in pancreatic cancer cell lines and increases their proliferation. Pancreatic tumor samples have increased levels of nuclear TRAIL-R2, which correlate with poor outcome of patients. These findings indicate that in the nucleus, death receptors can function as tumor promoters and might be therapeutic targets.

The intraerythrocytic stage of Plasmodium falciparum alters the characteristics of its host cell by exporting selected plasmodial proteins. Although it is clear that the physicochemical and immunobiological properties of the host cell are modulated during parasite development, the involved plasmodial proteins and their mode of action are not completely known. Using cetyltrimethylammonium bromide (CTAB) or benzyldimethyl-n-hexadecylammonium chloride (16-BAC) for the first dimension and SDS for the second dimension, we separated proteins from membranes of human erythrocytes and of erythrocytes infected with the malaria parasite P. falciparum. Protein spots were analyzed by MALDI-TOF/TOF MS and annotated in respective 2D master gels. By using the alternative 2D approach, characteristic host cell membrane proteins and, more importantly, membrane-associated and exported plasmodial proteins were identified that might play a role in parasite-induced host cell modulation.

Adaptive immune systems are present only in vertebrates. How do all the remaining animals withstand continuous attacks of permanently evolving pathogens? Even in the absence of adaptive immunity, every organism must be able to unambiguously distinguish ‘‘self’’ cells from any imaginable ‘‘nonself.’’ Here, we analyzed the function of highly polymorphic gene vCRL1, which is expressed in follicle and blood cells of Ciona intestinalis, pointing to possible recognition roles either during fertilization or in immune reactions. By using segregation analysis, we demonstrate that vCRL1 locus is not involved in the control of self-sterility. Interestingly, genetic knockdown of vCRL1 in all tissues or specifically in hemocytes results in a drastic developmental arrest during metamorphosis exactly when blood system formation in Ciona normally occurs. Our data demonstrate that vCRL1 gene might be essential for the establishment of a functional blood system in Ciona. Presumably, presence of the vCRL1 receptor on the surface of blood cells renders them as self, whereas any cell lacking it is referred to as nonself and will be consequently destroyed. We propose that individual-specific receptor vCRL1 might be utilized to facilitate somatic self/nonself discrimination.

Human pathogens often produce soluble protein toxins that generate pores inside membranes, resulting in the death of target cells and tissue damage. In pathogenic amoebae, this has been exemplified with amoebapores of the enteric protozoan parasite Entamoeba histolytica. Here we characterize acanthaporin, to our knowledge the first pore-forming toxin to be described from acanthamoebae, which are free-living, bacteria-feeding, unicellular organisms that are opportunistic pathogens of increasing importance and cause severe and often fatal diseases. We isolated acanthaporin from extracts of virulent Acanthamoeba culbertsoni by tracking its pore-forming activity, molecularly cloned the gene of its precursor and recombinantly expressed the mature protein in bacteria. Acanthaporin was cytotoxic for human neuronal cells and exerted antimicrobial activity against a variety of bacterial strains by permeabilizing their membranes. The tertiary structures of acanthaporin's active monomeric form and inactive dimeric form, both solved by NMR spectroscopy, revealed a currently unknown protein fold and a pH-dependent trigger mechanism of activation.

Novel peptidomimetics of type (I) are supplied with a protected aspartyl aldehyde moiety to increase lipophilicity.

Allicin and derivatives thereof inhibit the CAC1 cysteine proteases falcipain 2, rhodesain, cathepsin B and L in the low micromolar range. The structure-activity relationship revealed that only derivatives with primary carbon atom in vicinity to the thiosulfinate sulfur atom attacked by the active-site Cys residue are active against the target enzymes. Some compounds also show potent antiparasitic activity against Plasmodium falciparum and Trypanosoma brucei brucei.

In recent years, several novel relevant peanut allergens have been identified. Among those, a new member of the conglutin family was cloned by a phage display approach and initially annotated as Ara h 7.0101. Later, however, recloning of Ara h 7 revealed an alternate isoform, termed Ara h 7.0201. Because the natural Ara h 7 counterpart had not been found at the protein level in peanut extracts, the aim of the present study was to search for authentic natural Ara h 7 protein(s). To this end, enriched low molecular mass proteins (

Nck is a ubiquitously expressed, primarily cytosolic adapter protein consisting of one SH2 domain and three SH3 domains. It links receptor and nonreceptor tyrosine kinases to actin cytoskeleton reorganizing proteins. In T lymphocytes, Nck is a crucial component of signaling pathways for T cell activation and effector function. It recruits actin remodeling proteins to T cell receptor (TCR)-associated activation clusters and thereby initiates changes in cell polarity and morphology. Moreover, Nck is crucial for the TCR-induced mobilization of secretory vesicles to the cytotoxic immunological synapse. To identify the interactome of Nck in human T cells, we performed a systematic screen for interaction partners in untreated or pervanadate-treated cells. We used GST fusion proteins containing full length Nck, the combined SH3 domains or the individual SH3 and SH2 domains to precipitate putative Nck interactors from cellular lysates. Protein bands were excised from gels, processed by tryptic in-gel digestion and analyzed by mass spectrometry. Using this approach, we confirmed previously established interactions (e.g., with Slp76, CD3 epsilon, WASP, and WIPF1) and identified several novel putative Nck-binding proteins. We subsequently verified the SH2 domain binding to the actin-binding protein HIP55 and to FYB/ADAP, and the SH3-mediated binding to the nuclear proteins SFPQ/NONO. Using laser scanning microscopy, we provide new evidence for a nuclear localization of Nck in human T cells. Our data highlight the fundamental role of Nck in the TCR-to-cytoskeleton crosstalk and point to yet unknown nuclear functions of Nck also in T lymphocytes.

For the soil nematode Caenorhabditis elegans, microbes are both food source and potential pathogens. Intrinsic antibiotic agents such as antimicrobial peptides (AMP) are important to protect the worm against infection. Here, we show that among potential antimicrobial peptides of C. elegans, with respect to gene number, the majority belongs to the SPP-protein family which we named caenopores as they resemble structurally and functionally amoebapores. SPP-5 kills bacteria by permeabilizing their cytoplasmic membrane and displays pore-forming activity as judged by liposome depolarization. The antimicrobial polypeptide is required to cope with Escherichia coli, the regular food source of C. elegans in the laboratory, as worms devoid of this weapon develop poorly, permitting a substantial number of bacteria to survive in the intestine. As numerous caenopores exert their activity in the intestinal lumen, an environment mimicking with its acidic pH and the presence of hydrolytic enzymes, the interior of phagolysosomes, individual members may be operative in eliminating distinct groups of microorganisms that enter this tract by food consumption. Individual spp genes are induced upon contact with particular bacteria, whereas others are expressed regardless of the bacteria they live on. The multifarious caenopore family of antimicrobial peptides may have been a key event that enables C. elegans to live and survive in its natural habitat, on rotting organic material.

Over the last decade, an increasing prevalence of peanut allergies was observed worldwide. Peanuts are meanwhile categorized among the most dangerous food allergens. This is particularly relevant since peanut-derived ingredients are widely used in industrial food production. To minimize the problem of hidden food allergens causing severe anaphylactic reactions, pre-packaged food containing peanut components needs to be classified according to European ruling since 2005. Food companies search for strategies to reduce the allergenicity of peanut-derived food additives either by genetically altering the allergen content or by identifying peanut varieties with low levels of major allergens. In our study, we focused on peanut extracts from Indonesia that apparently contain lower levels of the major Arachis hypogaea allergen 1 (Ara h 1). Basic extracts of Virginia-type and Indonesian peanuts were compared by 1- and 2-DE. We identified more than hundred individual components in these extracts by MS and provide a high-resolution allergen map that also includes so far unknown fragments of major peanut allergens. The reduced level of Ara h 1 associated with a significantly lower abundance of the most potent peanut allergen Ara h 2 in various Indonesian peanuts was also confirmed by Western blotting with monoclonal antibodies and sera of allergic patients.

C-reactive protein (CRP) from the American horseshoe crab, Limulus polyphemus, exhibits complex membrane activities. Here, we describe the behavior of protein and lipid as CRP interacts with model liposomes and bacterial membranes. Limulus C-reactive protein (L-CRP) forms extended fibrilar structures that encapsulate liposomes in the presence of Ca2+. We have observed structures consistent in size and shape with these fibers bound to the surface of Gram-negative bacteria. The membranes of Limulus CRP-treated bacteria exhibit significantly different mechano-elastic properties than those of untreated bacteria. In vitro, bilayer lipids undergo a rigidification and reorganization of small domains. We suggest that these interactions reflect the protein's role as a primary defense molecule, functioning in the entrapment and killing of potential pathogens. (C) 2009 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Psoriasin, a member of the S100 family of calcium-binding proteins (S100A7) is highly upregulated in the skin of psoriasis patients. As it has recently been found to exhibit antimicrobial activity, an important role of psoriasin in surface defence has been suggested. The similarity of the three-dimensional structures of psoriasin and amoebapore A, an ancient antimicrobial, pore-forming peptide from Entamoeba histolytica, intrigued us to investigate whether the human psoriasin is also able to permeabilize bacterial membranes. Here, we demonstrate that psoriasin exerts pore-forming activity at pH values below 6 demonstrating that disruption of microbial membranes is the basis of its antimicrobial activity at low pH. Furthermore, the killing activity of psoriasin shows pH-dependent target specificity. At neutral pH, the Gram-negative bacterium E. coli is killed apparently without compromising its membrane, whereas at low pH exclusively the Gram-positive bacterium B. megaterium is killed by permeabilization of its cytoplasmic membrane.

The pentraxins are a family of highly conserved plasma proteins of metazoans known to function in immune defence. The canonical members, C-reactive protein and serum amyloid P component, have been identified in arthropods and humans. Mammalian pentraxins are known to bind lipid bilayers, and a pentraxin representative from the American horseshoe crab, Limulus polyphemus, binds and permeabilizes mammalian erythrocytes. Both activities are Ca2+-dependent. Utilizing model liposomes and planar lipid bilayers, in the present study we have investigated the membrane-active properties of the three pentraxin representatives from Limulus and show that all of the Limulus pentraxins permeabilize lipid bilayers. Mechanistically, Limulus C-reactive protein forms transmembrane pores in asymmetric planar lipid bilayers that mimic the outer membrane of Gram-negative bacteria and exhibits a Ca2+-independent form of membrane binding that may be sufficient for pore formation.

In a time of dramatically increasing resistance of microbes to all kinds of antibiotics, natural antimicrobial peptides and synthetic analogs thereof have emerged as compounds with potentially significant therapeutical applications against human pathogens. Only very few of these peptide antibiotics have been tested against protozoan pathogens that are a major cause of morbidity and mortality in large parts of the world. Here, we studied the effect of NK-2, a peptide representing the cationic core region of the lymphocytic effector protein NK-lysin, on the malaria parasite Plasmodium falciparum . Whereas noninfected red blood cells were hardly affected, human erythrocytes infected with the parasite were rapidly permeabilized by NK-2 in the micromolar range. Loss of plasma membrane asymmetry and concomitant exposure of phosphatidylserine upon infection appears to be the molecular basis for the observed target preference of NK-2, as can be demonstrated by annexin V binding. The peptide also affects the viability of the intracellular parasite, as evidenced by the drop in DNA content of cultured parasites. Accumulated evidence derived from permeabilization assays using parasites and liposomes as targets and from fluorescence microscopy of infected erythrocytes treated with fluorescently labeled NK-2 indicates that the positively charged peptide electrostatically interacts with the altered and negatively charged plasma membrane of the infected host cell and traverses this membrane as well as the parasitophorous vacuole membrane to reach its final target, the intracellular parasite. The apparent affinity for foreign membranes that resulted in the death of a eukaryotic parasite residing in human host cells makes NK-2 a promising template for novel anti-infectives.

A comprehensive screening of N-acylated aziridine (aziridide) based cysteine protease inhibitors containing either Boc-Leu-Caa (Caa=cyclic amino acid), Boc-Gly-Caa, or Boc-Phe-Ala attached to the aziridine nitrogen atom revealed Boc-(S)-Leu-(S)-Azy-(S,S)-Azi(OBn)(2) (18 a) as a highly potent cathepsin L (CL) inhibitor (K(i)=13 nM) (Azy=aziridine-2-carboxylate, Azi=aziridine-2,3-dicarboxylate). Docking studies, which also accounted for the unusual bonding situations (the flexibility and hybridization of the aziridides) predict that the inhibitor adopts a Y shape and spans across the entire active site cleft, binding into both the nonprimed and primed sites of CL.

The malaria parasite Plasmodium falciparum invades human red blood cells. Before infecting new erythrocytes, the merozoites have to exit their host cell to get into the blood plasma. Knowledge about the mechanism of egress is scarce, but it is thought that proteases are basically involved in this step. We have introduced a biotinylated dibenzyl aziridine-2,3-dicarboxylate (bADA) as an irreversible cysteine protease inhibitor to study the mechanism of merozoite release and to identify the proteases involved. The compound acts on parasite proteins in the digestive vacuole and in the host cell cytosol, as judged by fluorescence microscopy. The inhibitor blocks rupture of the host cell membrane, leading to clustered merozoite structures, as evidenced by immunoelectron microscopy. Interestingly, bADA did not prevent rupture of the parasitophorous vacuole membrane (PVM) that surrounds the parasite during the period of intraerythrocytic maturation. The compound appears to be a valuable template for the development of inhibitors specific for individual plasmodial proteases, which would be useful tools to dissect the molecular mechanisms underlying the process of merozoite release and consequently to develop potent antimalarial drugs.

Cysteine proteases have been implicated in a variety of processes essential for the survival and progression of the malarial parasite Plasmodium falciparum. Here, we synthesized a cysteine protease inhibitor that contains the electrophilic aziridine-2,3-dicarboxylic acid as the reactive agent and biotin as a targeting label. Diethyl ester and dibenzyl ester derivatives of the inhibitor were active against cathepsin L and the plasmodial protease falcipain 2, but only the latter displayed potent antiplasmodial activity against viable parasites. The morphological changes observed during the intraerythrocytic life stages of Plasmodium suggest that degradation of hemoglobin of the host cell is seriously affected, eventually leading to growth arrest and cell death of the parasites. After incubation of infected erythrocytes with the compound plasmodial proteins were captured, with the biotinyl group of the inhibitor serving as an affinity tag. Among these the cysteine proteases falcipain 2 and falcipain 3 were identified as potential target proteins of the compound as evidenced by tandem mass spectrometry. Apparently, the compound gets access to intracellular compartments and therein targets plasmodial cysteine proteases. Accordingly, the reagent described here appears to be a valuable template to develop cell-permeable, non-radioactive reagents that selectively target enzymes involved in pathogenicity of the parasite.

The adaptor protein Nck almost exclusively consists of one SH2 domain and three SH3 domains and plays an important role in linking receptor tyrosine kinases (and associated proteins) to modulators of the actin cytoskeleton. In T cells, Nck thereby connects T cell receptor signaling to the machinery of actin reorganization thus initiating changes in cell polarity required for T cell effector function. We previously showed that Nck interacts with the death factor FasL and is required for the recruitment of FasL to the cytotoxic immunological synapse upon recognition of a target cell (Lettau et al., PNAS 2006). Given the importance of Nck in T cell effector function, we now performed a systematic screening for interaction partners of the four individual interaction modules of Nck in primary and leukemic T cells. To this end, we expressed full length Nck, the three SH3 domains and the individual SH3 and SH2 domains of Nck as GST fusion proteins to precipitate binding partners from untreated or pervanadate-treated PHA blasts, Jurkat and HUT78 cells. Candidate binding proteins were cut from gels after Coomassie, Silver, Sypro Ruby or Flamingo Pink staining and processed by tryptic in gel digestion for mass spectrometrical analysis. Of several candidate-binding partners identified by the pulldown assays, we confirmed direct interaction by Far Western Blotting. As might be expected, we observe major differences in Nck binding proteins from resting versus activated T cells. Interestingly, the list of interactors not only points to known functions including recruitment of the WASP/Arp2/3 complex and the actin cytoskeleton but also to the recently described nuclear translocation and function of Nck, e.g. in damaged cells. Therefore, we are currently focusing on the verification of the latter Nck interactions in nuclear extracts to unravel this new aspect of Nck biology.