Recent developments in the molecular, biochemical and functional characterization of GPI8 and the GPI-anchoring mechanism [review]

Biogenesis of Extracellular Vesicles

Extracellular vesicles (EVs) refer to vesicles that are released by cells into the extracellular space. EVs mediate cell-to-cell communication via delivery of functional biomolecules between host and recipient cells. EVs can be categorised based on their mode of biogenesis and secretion and include apoptotic bodies, ectosomes or shedding microvesicles and exosomes among others. EVs have gained immense interest in recent years owing to their implications in pathophysiological conditions. Indeed, EVs have been proven useful in clinical applications as potential drug delivery vehicles and as source of diagnostic biomarkers. Despite the growing body of evidence supporting the clinical benefits, the processes involved in the biogenesis of EVs are poorly understood. Hence, it is critical to gain a deeper understanding of the underlying molecular machineries that ultimately govern the biogenesis and secretion of EVs. This chapter discusses the current knowledge on molecular mechanisms involved in the biogenesis of various subtypes of EVs.

Computational prediction of the effects of non-synonymous single nucleotide polymorphisms on the GPI-anchor transamidase subunit GPI8p of Plasmodium falciparum

Drug resistance is increasingly evolving in malaria parasites; hence, it is important to discover and establish alternative drug targets. In this context, GPI-anchor transamidase (GPI-T) is a potential drug target primarily of its crucial role in the development and survival of the parasite in the GPI anchor biosynthesis pathway. The present investigation was undertaken to explore the plausible effects of nsSNP on the structure and functions of GPI-T subunit GPI8p of Plasmodium falciparum. The GPI8p (PF3D7_1128700) was analyzed using various sequence-based and structure-based computational tools such as SIFT, PROVEAN, PredictSNP, SNAP2, I-Mutant, MuPro, ConSurf, NetSurfP, MUSTER, COACH server and STRING server. Of the 34 nsSNPs submitted for functional analysis, 18 nsSNPs (R124 L, N143 K, Y145 F, V157I, T195S, K379E, I392 K, I437 T, Y438H, N439D, Y441H, N442D, N448D, N451D, D457A, D457Y, I458 L and N460 K) were predicted to have deleterious effects on the protein GPI8p. Additionally, I-Mutant 2.0 and MuPro both showed a decrease in stability after mutation as a result of these nsSNPs, suggesting the destabilization of protein. ConSurf findings suggest that most of the regions were highly conserved. In addition, COACH server was used to predict the ligand binding sites. It was found that no mutation was present at the predicted ligand binding site. The results of the STRING database showed that the protein GPI8p interacts with those proteins which either involve the biosynthetic process of attaching GPI anchor to protein or GPI anchor. The present study suggested that the GPI8p could be a novel target for anti-malarial drugs, which provides significant details for further experimentation.

Bridging the GAPs in plant reproduction: a comparison of plant and animal GPI-anchored proteins

Glycosylphosphatidylinositol (GPI)-anchored proteins (GAPs) are a unique type of membrane-associated proteins in eukaryotes. GPI and GAP biogenesis and function have been well studied in non-plant models and play an important role in the fertility of mouse sperm and egg. Although GPI and GAP biogenesis and function in plants are less known, they are critical for flowering plant reproduction because of their essential roles in the fertility of the male and female gametophytes. In Eukaryotes, GPI, a glycolipid molecule, can be post-translationally attached to proteins to serve as an anchor in the plasma membrane. GPI-anchoring, compared to other modes of membrane attachment and lipidation processes, localizes proteins to the extracellular portion of the plasma membrane and confers several unique attributes including specialized sorting during secretion, molecular painting onto membranes, and enzyme-mediated release of protein through anchor cleavage. While the biosynthesis, structure, and role of GPI are mostly studied in mammals, yeast and protists, the function of GPI and GAPs in plants is being discovered, particularly in gametophyte development and function. Here, we review GPI biosynthesis, protein attachment, and remodeling in plants with insights about this process in mammals. Additionally, we summarize the reproductive phenotypes of all loss of function mutations in Arabidopsis GPI biosynthesis and GAP genes and compare these to the reproductive phenotypes seen in mice to serve as a framework to identify gaps in our understanding of plant GPI and GAPs. In addition, we present an analysis on the gametophyte expression of all Arabidopsis GAPs to assist in further research on the role of GPI and GAPs in all aspects of the gametophyte generation in the life cycle of a plant.

A case report: paroxysmal nocturnal hemoglobinuria and systemic lupus erythematosus association

Paroxysmal nocturnal hemoglobinuria (PNH) is defined by acquired intravascular hemolytic anemia, thrombosis and bone marrow failure with pancytopenia. Systemic lupus erythematosus (SLE) also appears as an autoimmune disease. The coexistence of both is rarely reported. Here we report the case of a 30-year-old female presenting with pancytopenia and diagnosed as SLE, who also had a PNH clone. Bone marrow biopsy did not support hypoplastic anemia. The patient was then followed up with the consideration of the existence of a PNH clone with SLE. She was treated by the rheumatology department and complete blood count improved under immunosuppressive treatment. The coexistence of CD59–CD55 deficiency with autoimmune diseases has been reported. It is an important example in terms of receiving clinical response with SLE-specific treatment.

The Temperature-Dependent Retention of Introns in GPI8 Transcripts Contributes to a Drooping and Fragile Shoot Phenotype in Rice

Attachment of glycosylphosphatidylinositols (GPIs) to the C-termini of proteins is one of the most common posttranslational modifications in eukaryotic cells. GPI8/PIG-K is the catalytic subunit of the GPI transamidase complex catalyzing the transfer en bloc GPI to proteins. In this study, a T-DNA insertional mutant of rice with temperature-dependent drooping and fragile (df) shoots phenotype was isolated. The insertion site of the T-DNA fragment was 879 bp downstream of the stop codon of the OsGPI8 gene, which caused introns retention in the gene transcripts, especially at higher temperatures. A complementation test confirmed that this change in the OsGPI8 transcripts was responsible for the mutant phenotype. Compared to control plants, internodes of the df mutant showed a thinner shell with a reduced cell number in the transverse direction, and an inhomogeneous secondary wall layer in bundle sheath cells, while many sclerenchyma cells at the tops of the main veins of df leaves were shrunken and their walls were thinner. The df plants also displayed a major reduction in cellulose and lignin content in both culms and leaves. Our data indicate that GPI anchor proteins play important roles in biosynthesis and accumulation of cell wall material, cell shape, and cell division in rice.

Structural basis of ribosomal peptide macrocyclization in plants

Constrained, cyclic peptides encoded by plant genes represent a new generation of drug leads. Evolution has repeatedly recruited the Cys-protease asparaginyl endopeptidase (AEP) to perform their head-to-tail ligation. These macrocyclization reactions use the substrates amino terminus instead of water to deacylate, so a peptide bond is formed. How solvent-exposed plant AEPs macrocyclize is poorly understood. Here we present the crystal structure of an active plant AEP from the common sunflower, Helianthus annuus. The active site contained electron density for a tetrahedral intermediate with partial occupancy that predicted a binding mode for peptide macrocyclization. By substituting catalytic residues we could alter the ratio of cyclic to acyclic products. Moreover, we showed AEPs from other species lacking cyclic peptides can perform macrocyclization under favorable pH conditions. This structural characterization of AEP presents a logical framework for engineering superior enzymes that generate macrocyclic peptide drug leads.

Most proteins are long, chain-like molecules that have two ends respectively called the N-terminus and C-terminus. However, certain proteins can close on themselves to become circular. This requires a chemical reaction between the N- and C-termini, which creates a strong bond between the two extremities.

To go through this ‘cyclization’ process, a straight protein attaches to a certain type of protease, a class of enzyme that usually cuts proteins into smaller pieces. In plants that are distantly related, the same group of enzymes – called AEPs – has been selected to perform cyclization. Here, Haywood et al. study an AEP enzyme from sunflowers: they identify what about this enzyme’s structure is important to drive the complex chemical reaction that results in the protein being cyclized rather than simply cut.

Using a technique called X-ray crystallography to see the positions of individual atoms in the enzyme, Haywood et al. caught a snapshot of the enzyme. Its structure explained how the enzyme’s shape can guide cyclization. In particular, the part of the enzyme that binds to the proteins, the active site, was relatively flat and open, but also flexible: this helped the N and C-termini react with each other and close the protein. Further experiments artificially mutated specific areas of the enzyme, which helped determine exactly which elements guide this succession of chemical reactions.

The activity of AEPs is influenced by their local environment, such as acidity. In fact, Haywood et al. showed that certain AEPs, which do not normally carry out cyclization, can start performing this role when exposed to a different level of acidity.

The pharmaceutical industry is increasingly interested in circular proteins, as these are stable, easily used by the body, and can be genetically customized to act only on specific targets. If the cyclization process is better understood, and then harnessed, new drug compounds could be produced.

Diagnosis of Paroxysmal Nocturnal Hemoglobinuria: Recent Advances

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoietic stem cell disorder with its protean clinical manifestations. This is due to partial or complete absence of 'glycophosphatidyl-inositol-anchor proteins' (GPI-AP). The main aim of this review is to highlight various diagnostic modalities available, basic principle of each test and recent advances in the diagnosis of PNH. Recently among various tests available, the flow cytometry has become 'the gold standard' for PNH testing. In order to overcome the difficulties encountered by the testing and research laboratories throughout the world, International Clinical Cytometry Society has come up with guidelines regarding the indications for testing, protocol for sample collection, processing, panel of antibodies as well as gating strategies to be used, how to interpret the test and reporting format to be used. It is essential to test at least two GPI-linked markers on at least two different lineages particularly on red cells and granulocytes/monocytes. The fluorescent aerolysin combined with other monoclonal antibodies in multicolour flow cytometry offered an improved assay not only for diagnosis but also for monitoring of PNH clones. It is equally important to diagnose this rare entity with high index of suspicion.

Structure and function of legumain in health and disease

The last years have seen a steady increase in our understanding of legumain biology that is driven from two largely uncoupled research arenas, the mammalian and the plant legumain field. Research on legumain, which is also referred to as asparaginyl endopeptidase (AEP) or vacuolar processing enzyme (VPE), is slivered, however. Here we summarise recent important findings and put them into a common perspective. Legumain is usually associated with its cysteine endopeptidase activity in lysosomes where it contributes to antigen processing for class II MHC presentation. However, newly recognized functions disperse previously assumed boundaries with respect to their cellular compartmentalisation and enzymatic activities. Legumain is also found extracellularly and even translocates to the cytosol and the nucleus, with seemingly incompatible pH and redox potential. These different milieus translate into changes of legumain's molecular properties, including its (auto-)activation, conformational stability and enzymatic functions. Contrasting its endopeptidase activity, legumain can develop a carboxypeptidase activity which remains stable at neutral pH. Moreover, legumain features a peptide ligase activity, with intriguing mechanistic peculiarities in plant and human isoforms. In pathological settings, such as cancer or Alzheimer's disease, the proper association of legumain activities with the corresponding cellular compartments is breached. Legumain's increasingly recognized physiological and pathological roles also indicate future research opportunities in this vibrant field.

pigk Mutation underlies macho behavior and affects Rohon-Beard cell excitability

The study of touch-evoked behavior allows investigation of both the cells and circuits that generate a response to tactile stimulation. We investigate a touch-insensitive zebrafish mutant, macho (maco), previously shown to have reduced sodium current amplitude and lack of action potential firing in sensory neurons. In the genomes of mutant but not wild-type embryos, we identify a mutation in the pigk gene. The encoded protein, PigK, functions in attachment of glycophosphatidylinositol anchors to precursor proteins. In wild-type embryos, pigk mRNA is present at times when mutant embryos display behavioral phenotypes. Consistent with the predicted loss of function induced by the mutation, knock-down of PigK phenocopies maco touch insensitivity and leads to reduced sodium current (INa) amplitudes in sensory neurons. We further test whether the genetic defect in pigk underlies the maco phenotype by overexpressing wild-type pigk in mutant embryos. We find that ubiquitous expression of wild-type pigk rescues the touch response in maco mutants. In addition, for maco mutants, expression of wild-type pigk restricted to sensory neurons rescues sodium current amplitudes and action potential firing in sensory neurons. However, expression of wild-type pigk limited to sensory cells of mutant embryos does not allow rescue of the behavioral touch response. Our results demonstrate an essential role for pigk in generation of the touch response beyond that required for maintenance of proper INa density and action potential firing in sensory neurons.

Glycosylphosphatidylinositol-anchored proteins in Fusarium graminearum: inventory, variability, and virulence

The contribution of cell surface proteins to plant pathogenicity of fungi is not well understood. As such, the objective of this study was to investigate the functions and importance of glycosylphosphatidylinositol-anchored proteins (GPI-APs) in the wheat pathogen F. graminearum. GPI-APs are surface proteins that are attached to either the membrane or cell wall. In order to simultaneously disrupt several GPI-APs, a phosphoethanolamine transferase-encoding gene gpi7 was deleted and the resultant mutant characterized in terms of growth, development, and virulence. The Δgpi7 mutants exhibited slower radial growth rates and aberrantly shaped macroconidia. Furthermore, virulence tests and microscopic analyses indicated that Gpi7 is required for ramification of the fungus throughout the rachis of wheat heads. In parallel, bioinformatics tools were utilized to predict and inventory GPI-APs within the proteome of F. graminearum. Two of the genes identified in this screen (FGSG_01588 and FGSG_08844) displayed isolate-specific length variability as observed for other fungal cell wall adhesion genes. Nevertheless, deletion of these genes failed to reveal obvious defects in growth, development, or virulence. This research demonstrates the global importance of GPI-APs to in planta proliferation in F. graminearum, and also highlights the potential of individual GPI-APs as diagnostic markers.

Effects of FlAsH/tetracysteine (TC) Tag on PrP proteolysis and PrPres formation by TC-scanning

Protein-protein interactions associated with proteolytic processing and aggregation are integral to normal and pathological aspects of prion protein (PrP) biology. Characterization of these interactions requires the identification of amino acid residues involved. The FlAsH/tetracysteine (FlAsH/TC) tag is a small fluorescent tag amenable to insertion at internal sites in proteins. In this study, we used serial FlAsH/TC insertions (TC-scanning) as a probe to characterize sites of protein-protein interaction between PrP and other molecules. To explore this application in the context of substrate-protease interactions, we analyzed the effect of FlAsH/TC insertions on proteolysis of cellular prion protein (PrPsen) in in vitro reactions and generation of the C1 metabolic fragment of PrPsen in live neuroblastoma cells. The influence of FlAsH/TC insertion was evaluated by TC-scanning across the cleavage sites of each protease. The results showed that FlAsH/TC inhibited protease cleavage only within limited ranges of the cleavage sites, which varied from about one to six residues in width, depending on the protease, providing an estimate of the PrP residues interacting with each protease. TC-scanning was also used to probe a different type of protein-protein interaction: the conformational conversion of FlAsH-PrPsen to the prion disease-associated isoform, PrPres. PrP constructs with FlAsH/TC insertions at residues 90-96 but not 97-101 were converted to FlAsH-PrPres, identifying a boundary separating loosely versus compactly folded regions of PrPres. Our observations demonstrate that TC-scanning with the FlAsH/TC tag can be a versatile method for probing protein-protein interactions and folding processes.

Mannose receptor (MR) engagement by mesothelin GPI anchor polarizes tumor-associated macrophages and is blocked by anti-MR human recombinant antibody

Tumor-infiltrating macrophages respond to microenvironmental signals by developing a tumor-associated phenotype characterized by high expression of mannose receptor (MR, CD206). Antibody cross-linking of CD206 triggers anergy in dendritic cells and CD206 engagement by tumoral mucins activates an immune suppressive phenotype in tumor-associated macrophages (TAMs). Many tumor antigens are heavily glycosylated, such as tumoral mucins, and/or attached to tumor cells by mannose residue-containing glycolipids (GPI anchors), as for example mesothelin and the family of carcinoembryonic antigen (CEA). However, the binding to mannose receptor of soluble tumor antigen GPI anchors via mannose residues has not been systematically studied. To address this question, we analyzed the binding of tumor-released mesothelin to ascites-infiltrating macrophages from ovarian cancer patients. We also modeled functional interactions between macrophages and soluble mesothelin using an in vitro system of co-culture in transwells of healthy donor macrophages with human ovarian cancer cell lines. We found that soluble mesothelin bound to human macrophages and that the binding depended on the presence of GPI anchor and of mannose receptor. We next challenged the system with antibodies directed against the mannose receptor domain 4 (CDR4-MR). We isolated three novel anti-CDR4-MR human recombinant antibodies (scFv) using a yeast-display library of human scFv. Anti-CDR4-MR scFv #G11 could block mesothelin binding to macrophages and prevent tumor-induced phenotype polarization of CD206(low) macrophages towards TAMs. Our findings indicate that tumor-released mesothelin is linked to GPI anchor, engages macrophage mannose receptor, and contributes to macrophage polarization towards TAMs. We propose that compounds able to block tumor antigen GPI anchor/CD206 interactions, such as our novel anti-CRD4-MR scFv, could prevent tumor-induced TAM polarization and have therapeutic potential against ovarian cancer, through polarization control of tumor-infiltrating innate immune cells.

Pathogenesis of chagas' disease: parasite persistence and autoimmunity

Acute Trypanosoma cruzi infections can be asymptomatic, but chronically infected individuals can die of Chagas' disease. The transfer of the parasite mitochondrial kinetoplast DNA (kDNA) minicircle to the genome of chagasic patients can explain the pathogenesis of the disease; in cases of Chagas' disease with evident cardiomyopathy, the kDNA minicircles integrate mainly into retrotransposons at several chromosomes, but the minicircles are also detected in coding regions of genes that regulate cell growth, differentiation, and immune responses. An accurate evaluation of the role played by the genotype alterations in the autoimmune rejection of self-tissues in Chagas' disease is achieved with the cross-kingdom chicken model system, which is refractory to T. cruzi infections. The inoculation of T. cruzi into embryonated eggs prior to incubation generates parasite-free chicks, which retain the kDNA minicircle sequence mainly in the macrochromosome coding genes. Crossbreeding transfers the kDNA mutations to the chicken progeny. The kDNA-mutated chickens develop severe cardiomyopathy in adult life and die of heart failure. The phenotyping of the lesions revealed that cytotoxic CD45, CD8(+) γδ, and CD8α(+) T lymphocytes carry out the rejection of the chicken heart. These results suggest that the inflammatory cardiomyopathy of Chagas' disease is a genetically driven autoimmune disease.

Targeting of voltage-gated calcium channel α2δ-1 subunit to lipid rafts is independent from a GPI-anchoring motif

Voltage-gated calcium channels (Ca_v) exist as heteromultimers comprising a pore-forming α₁ with accessory β and α₂δ subunits which modify channel trafficking and function. We previously showed that α₂δ-1 (and likely the other mammalian α₂δ isoforms - α₂δ-2, 3 and 4) is required for targeting Ca_vs to lipid rafts, although the mechanism remains unclear. Whilst originally understood to have a classical type I transmembrane (TM) topology, recent evidence suggests the α₂δ subunit contains a glycosylphosphatidylinositol (GPI)-anchor that mediates its association with lipid rafts. To test this notion, we have used a strategy based on the expression of chimera, where the reported GPI-anchoring sequences in the gabapentinoid-sensitive α₂δ-1 subunit have been substituted with those of a functionally inert Type I TM-spanning protein – PIN-G. Using imaging, electrophysiology and biochemistry, we find that lipid raft association of PIN-α₂δ is unaffected by substitution of the GPI motif with the TM domain of PIN-G. Moreover, the presence of the GPI motif alone is not sufficient for raft localisation, suggesting that upstream residues are required. GPI-anchoring is susceptible to phosphatidylinositol-phospholipase C (PI-PLC) cleavage. However, whilst raft localisation of PIN-α₂δ is disrupted by PI-PLC treatment, this is assay-dependent and non-specific effects of PI-PLC are observed on the distribution of the endogenous raft marker, caveolin, but not flotillin. Taken together, these data are most consistent with a model where α₂δ-1 retains its type I transmembrane topology and its targeting to lipid rafts is governed by sequences upstream of the putative GPI anchor, that promote protein-protein, rather than lipid-lipid interactions.

Altered GPI modification of insect AChE improves tolerance to organophosphate insecticides

The olive fruit fly Bactrocera oleae is the most destructive and intractable pest of olives. The management of B. oleae has been based on the use of organophosphate (OP) insecticides, a practice that induced resistance. OP-resistance in the olive fly was previously shown to be associated with two mutations in the acetylcholinesterase (AChE) enzyme that, apparently, hinder the entrance of the OP into the active site. The search for additional mutations in the ace gene that encodes AChE revealed a short deletion of three glutamines (Δ3Q) from a stretch of five glutamines, in the C-terminal peptide that is normally cleaved and substituted by a GPI anchor. We verified that AChEs from B. oleae and other Dipterans are actually GPI-anchored, although this is not predicted by the "big-PI" algorithm. The Δ3Q mutation shortens the unusually long hydrophilic spacer that follows the predicted GPI attachment site and may thus improve the efficiency of GPI anchor addition. We expressed the wild type B. oleae AChE, the natural mutant Δ3Q and a constructed mutant lacking all 5 consecutive glutamines (Δ5Q) in COS cells and compared their kinetic properties. All constructs presented identical K(m) and k(cat) values, in agreement with the fact that the mutations did not affect the catalytic domain of the enzyme. In contrast, the mutants produced higher AChE activity, suggesting that a higher proportion of the precursor protein becomes GPI-anchored. An increase in the number of GPI-anchored molecules in the synaptic cleft may reduce the sensitivity to insecticides.

Molecular mechanisms of host cell invasion by Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease, is an obligate intracellular protozoan pathogen. Overlapping mechanisms ensure successful infection, yet the relationship between these cellular events and clinical disease remains obscure. This review explores the process of cell invasion from the perspective of cell surface interactions, intracellular signaling, modulation of the host cytoskeleton and endosomal compartment, and the intracellular innate immune response to infection.

Assessing lead time of selected ovarian cancer biomarkers: a nested case-control study

Background

CA125, human epididymis protein 4 (HE4), mesothelin, B7-H4, decoy receptor 3 (DcR3), and spondin-2 have been identified as potential ovarian cancer biomarkers. Except for CA125, their behavior in the prediagnostic period has not been evaluated.

Methods

Immunoassays were used to determine concentrations of CA125, HE4, mesothelin, B7-H4, DcR3, and spondin-2 proteins in prediagnostic serum specimens (1–11 samples per participant) that were contributed 0–18 years before ovarian cancer diagnosis from 34 patients with ovarian cancer (15 with advanced-stage serous carcinoma) and during a comparable time interval before the reference date from 70 matched control subjects who were participating in the Carotene and Retinol Efficacy Trial. Lowess curves were fit to biomarker levels in cancer patients and control subjects separately to summarize mean levels over time. Receiver operating characteristic curves were plotted, and area-under-the curve (AUC) statistics were computed to summarize the discrimination ability of these biomarkers by time before diagnosis.

Results

Smoothed mean concentrations of CA125, HE4, and mesothelin (but not of B7-H4, DcR3, and spondin-2) began to increase (visually) in cancer patients relative to control subjects approximately 3 years before diagnosis but reached detectable elevations only within the final year before diagnosis. In descriptive receiver operating characteristic analyses, the discriminatory power of these biomarkers was limited (AUC statistics range = 0.56–0.75) but showed increasing accuracy with time approaching diagnosis (eg, AUC statistics for CA125 were 0.57, 0.68, and 0.74 for ≥4, 2–4, and <2 years before diagnosis, respectively).

Conclusion

Serum concentrations of CA125, HE4, and mesothelin may provide evidence of ovarian cancer 3 years before clinical diagnosis, but the likely lead time associated with these markers appears to be less than 1 year.

The global cysteine peptidase landscape in parasites

The accumulation of sequenced genomes has expanded the already sizeable population of cysteine peptidases from parasites. Characterization of a few of these enzymes has ascribed key roles to peptidases in parasite life cycles and has also shed light on mechanisms of pathogenesis. Here we discuss recent observations on the physiological activities of cysteine peptidases of parasitic organisms, paired with a global view of all cysteine peptidases from the MEROPS database grouped by similarity. This snapshot of the landscape of parasite cysteine peptidases is complex and highly populated, suggesting that expansion of research beyond the few 'model' parasite peptidases is now timely.

Lipid-modified morphogens: functions of fats

Despite their location in the aqueous extracellular environment, a number of secreted proteins carry hydrophobic lipid modifications. These modifications include glycosylphosphatidylinositol, cholesterol, and both saturated and unsaturated fatty acids, and they are attached in the secretory pathway by different classes of enzymes. Lipid attachments make crucial contributions to protein function in vivo through a diverse array of mechanisms. They can promote protein maturation and secretion, membrane tethering, targeting to specific membrane subdomains, or receptor binding and activation. Additionally, secretion of lipid-modified morphogens of the Wnt and Hh families requires dedicated accessory proteins and may involve their packaging into lipoprotein particles for long-range transport.

Perspectives on Trypanosoma cruzi-induced heart disease (Chagas disease)

Chagas disease is caused by the parasite Trypanosoma cruzi. It is a common cause of heart disease in endemic areas of Latin America. The year 2009 marks the 100th anniversary of the discovery of T cruzi infection and Chagas disease by the Brazilian physician Carlos Chagas. Chagasic cardiomyopathy develops in from 10% to 30% of persons who are chronically infected with this parasite. Echocardiography and magnetic resonance imaging (MRI) are important modalities in the evaluation and prognostication of individuals with chagasic heart disease. The etiology of chagasic heart disease likely is multifactorial. Parasite persistence, autoimmunity, and microvascular abnormalities have been studied extensively as possible pathogenic mechanisms. Experimental studies suggest that alterations in cardiac gap junctions may be etiologic in the pathogenesis of conduction abnormalities. The diagnosis of chronic Chagas disease is made by serology. The treatment of this infection has shortcomings that need to be addressed. Cardiac transplantation and bone marrow stem cell therapy for persons with Chagas disease have received increasing research attention in recent years.

Characterization of the glycosylphosphatidylinositol-anchor signal sequence of human Cryptic with a hydrophilic extension

Epidermal Growth Factor-Cripto-1/FRL-1/Cryptic (EGF-CFC) proteins, including human Cripto-1 (hCFC2/hCR-1) and human Cryptic (hCFC1), are membrane-associated Nodal co-receptors, which have critical roles in vertebrate development. Most of the EGF-CFC proteins have been experimentally proven or predicted to be glycosylphosphatidylinositol (GPI)-anchored proteins. However, unlike other EGF-CFC proteins, hCFC1 does not exhibit a typical GPI-signal sequence, containing a 32-amino acid hydrophilic extension in its COOH-terminal end. Here we experimentally demonstrate that the COOH-terminal sequence of hCFC1 functions as a GPI-anchoring signal. Moreover, addition of a hydrophilic epitope tag of 55-amino acids (V5-His) after the GPI signal of hCR-1 interfered with generation of a GPI-anchored form of hCR-1. In contrast, addition of the same epitope tag to the end of GPI signal of hCFC1 did not affect the GPI-attachment of hCFC1. The COOH-terminal signal of hCFC1 could produce two different forms of the protein; a GPI-anchored form and an unprocessed form which was more prone to be secreted into the conditioned medium. The hydrophilic extension of hCFC1 negatively regulates the activity of hCFC1 as a Nodal co-receptor. These results demonstrate the presence of endogenous GPI-signal sequence with a hydrophilic extension, which can generate both GPI-anchored and soluble forms of the protein.

A small deletion in the olive fly acetylcholinesterase gene associated with high levels of organophosphate resistance

Organophosphate resistance in the olive fly was previously shown to associate with two point mutations in the ace gene. The frequency of these mutations was monitored in Bactrocera oleae individuals of increasing resistance. In spite of the difference in resistance among the individuals, there was no correlation between mutation frequencies and resistance level, indicating that other factors may contribute to this variation. The search for additional mutations in the ace gene of highly resistant insects revealed a small deletion at the carboxyl terminal of the protein (termed Delta3Q). Significant correlation was shown between the mutation frequency and resistance level in natural populations. In addition, remaining activity of acetylcholinesterase enzyme (AChE) after dimethoate inhibition was higher in genotypes carrying the mutation. These results strongly suggest a role of Delta3Q in high levels of organophosphate (OP) resistance. Interestingly, the carboxyl terminal of AChE is normally cleaved and substituted by a glycosylphosphatidylinositol (GPI) anchor. We hypothesize that Delta3Q may improve GPI anchoring, thus increasing the amount of AChE that reaches the synaptic cleft. In this way, despite the presence of insecticide, enough enzyme would remain in the cleft for its normal role of acetylcholine hydrolysis, allowing the insect to survive. This provides a previously un-described mechanism of resistance.

Previously unrecognized vaccine candidates control Trypanosoma cruzi infection and immunopathology in mice

Trypanosoma cruzi is the etiologic agent of Chagas' disease, a major health problem in Latin America and an emerging infectious disease in the United States. Previously, we screened a T. cruzi sequence database by a computational-bioinformatic approach and identified antigens that exhibited the characteristics of good vaccine candidates. In this study, we tested the vaccine efficacy of three of the putative candidate antigens against T. cruzi infection and disease in a mouse model. C57BL/6 mice vaccinated with T. cruzi G1 (TcG1)-, TcG2-, or TcG4-encoding plasmids and cytokine (interleukin-12 and granulocyte-macrophage colony-stimulating factor) expression plasmids elicited a strong Th1-type antibody response dominated by immunoglobulin G2b (IgG2b)/IgG1 isotypes. The dominant IgG2b/IgG1 antibody response was maintained after a challenge infection and was associated with 50 to 90% control of the acute-phase tissue parasite burden and an almost undetectable level of tissue parasites during the chronic phase, as determined by a sensitive T. cruzi 18S rRNA gene-specific real-time PCR approach. Splenocytes from vaccinated-and-infected mice, compared to unvaccinated-and-infected mice, exhibited decreased (approximately 50% lower) proliferation and gamma interferon (IFN-gamma) production when stimulated in vitro with T. cruzi antigens, thus suggesting that protection from challenge infection was not provided by an active T-cell response. Subsequently, the serum and cardiac levels of IFN-gamma and tumor necrosis factor alpha and infiltration of inflammatory infiltrate in the heart were decreased in vaccinated mice during the course of infection and chronic disease development. Taken together, these results demonstrate the identification of novel vaccine candidates that provided protection from T. cruzi-induced immunopathology in experimental mice.

Impairment of cell division of Trypanosoma cruzi epimastigotes

The mechanisms that facilitate the adaptation of Trypanosoma cruzi to two distinct hosts, insect and vertebrate, are poorly understood, in part due to the limited ability to perform gene disruption studies by homologous recombination. This report describes a developmentally-defective phenotype that resulted from integration of a drug marker adjacent to the GAPDH gene in T. cruzi.