Phosphoglycosylation of a secreted acid phosphatase from Leishmania donovani

Comparison of biosynthetic zinc oxide nanoparticle and glucantime cytotoxic effects on Leishmania major (MRHO/IR/75/ER)

Currently, zinc oxide (ZnO) particles are used in nanotechnology to destroy a wide range of microorganisms. Although pentavalent antimony compounds are used as antileishmanial drugs, they are associated with several limitations and side effects. Therefore, it is always desirable to try to find new and effective treatments. The aim of this research is to determine the antileishmanial effect of ZnO particles in comparison to the Antimoan Meglumine compound on promastigotes and amastigotes of Leishmania major (MRHO/IR/75/ER). After the extraction and purification of macrophages from the peritoneal cavity of C57BL/6 mice, L. major parasites were cultured in Roswell Park Memorial Institute-1640 culture medium containing fetal bovine serum (FBS) 10% and antibiotic. In this experimental study, the effect of different concentrations of nanoparticles was investigated using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) colorimetric method, in comparison to the glucantime on promastigotes, amastigotes and healthy macrophages in the culture medium. The amount of light absorption of the obtained color from the regeneration of tetrazolium salt to the product color of formazan by the parasite was measured by an enzyme-linked immunosorbent assay (ELISA) reader, and the IC50 value was calculated. IC50 after 24 h of incubation was calculated as IC50 = 358.6 µg/mL. The results showed, that the efficacy of ZnO nanoparticles was favorable and dose-dependent. The concentration of 500 µg/mL of ZnO nanoparticles induced 84.67% apoptosis after 72. Also, the toxicity of nanoparticles was less than the drug. Nanoparticles exert their cytotoxic effects by inducing apoptosis. They can be suitable candidates in the pharmaceutical industry in the future.

C-reactive protein binds to short phosphoglycan repeats of Leishmania secreted proteophosphoglycans and activates complement

Human C-reactive protein (CRP) binds to lipophosphoglycan (LPG), a virulence factor of Leishmania spp., through the repeating phosphodisaccharide region. We report here that both major components of promastigote secretory gel (PSG), the filamentous proteophosphoglycan (fPPG) and the secreted acid phosphatase (ScAP), are also ligands. CRP binding was mainly associated with the flagellar pocket when LPG deficient Leishmania mexicana parasites were examined by fluorescent microscopy, consistent with binding to secreted material. ScAP is a major ligand in purified fPPG from parasite culture as demonstrated by much reduced binding to a ScAP deficient mutant fPPG in plate binding assays and ligand blotting. Nevertheless, in sandfly derived PSG fPPG is a major component and the major CRP binding component. Previously we showed high avidity of CRP for LPG ligand required multiple disaccharide repeats. ScAP and fPPG only have short repeats but they retain high avidity for CRP revealed by surface plasmon resonance because they are found in multiple copies on the phosphoglycan. The fPPG from many species such as L. donovani and L. mexicana bound CRP strongly but L. tropica and L. amazonensis had low amounts of binding. The extent of side chain substitution of [-PO4-6Galβ1-4Manα1-] disaccharides correlates inversely with binding of CRP. The ligand for the CRP on different species all had similar binding avidity as the half maximal binding concentration was similar. Since the PSG is injected with the parasites into host blood pools and phosphoglycans (PG) are known to deplete complement, we showed that CRP makes a significant contribution to the activation of complement by PSG using serum from naive donors.

Effects of Specific Electric Field Stimulation on the Release and Activity of Secreted Acid Phosphatases from Leishmania tarentolae and Implications for Therapy

Leishmaniasis is a neglected tropical disease with 1.6 million new cases reported each year. However, there are few safe, effective, and affordable treatments provided to those affected by this disease. Still under-appreciated as potential pharmaceutical targets, especially for cutaneous leishmaniasis infections, are the two isozymes of secreted acid phosphatase (SAP). These enzymes are involved in the survival of the parasite in the sand fly vector, and in infecting host macrophages. While the application of electric or electromagnetic fields as a medicinal therapeutic is not new, the utility of electric field application for the treatment of leishmaniasis is under studied. Studies involving the effects of electric fields on the cell secretion of SAP or the activity of SAP that has been secreted prior to electrical stimulation have not yet been reported. This work is the first report on the effect of specific electric fields on the activity of Leishmaniatarentolae secreted acid phosphatases and the modulation of this secretion from the cells. In addition, the kinetic constants for the enzyme isoforms were determined as a function of days in culture and removal of carbohydrate from the glycosylated enzymes, while using a glycosidase, was shown to affect these kinetic constants.

Leishmania cell wall as a potent target for antiparasitic drugs. A focus on the glycoconjugates

Although leishmaniasis has been studied for over a century, the fight against cutaneous, mucocutaneous and visceral forms of the disease remains a hot topic. This review refers to the parasitic cell wall and more particularly to the constitutive glycoconjugates. The structures of the main glycolipids and glycoproteins, which are species-dependent, are described. The focus is on the disturbance of the lipid membrane by existing drugs and possible new ones, in order to develop future therapeutic agents.

N-linked glycosylation in Archaea: a structural, functional, and genetic analysis

N-glycosylation of proteins is one of the most prevalent posttranslational modifications in nature. Accordingly, a pathway with shared commonalities is found in all three domains of life. While excellent model systems have been developed for studying N-glycosylation in both Eukarya and Bacteria, an understanding of this process in Archaea was hampered until recently by a lack of effective molecular tools. However, within the last decade, impressive advances in the study of the archaeal version of this important pathway have been made for halophiles, methanogens, and thermoacidophiles, combining glycan structural information obtained by mass spectrometry with bioinformatic, genetic, biochemical, and enzymatic data. These studies reveal both features shared with the eukaryal and bacterial domains and novel archaeon-specific aspects. Unique features of N-glycosylation in Archaea include the presence of unusual dolichol lipid carriers, the use of a variety of linking sugars that connect the glycan to proteins, the presence of novel sugars as glycan constituents, the presence of two very different N-linked glycans attached to the same protein, and the ability to vary the N-glycan composition under different growth conditions. These advances are the focus of this review, with an emphasis on N-glycosylation pathways in Haloferax, Methanococcus, and Sulfolobus.

Leishmania major survival in selective Phlebotomus papatasi sand fly vector requires a specific SCG-encoded lipophosphoglycan galactosylation pattern

Phlebotomine sand flies that transmit the protozoan parasite Leishmania differ greatly in their ability to support different parasite species or strains in the laboratory: while some show considerable selectivity, others are more permissive. In “selective” sand flies, Leishmania binding and survival in the fly midgut typically depends upon the abundant promastigote surface adhesin lipophosphoglycan (LPG), which exhibits species- and strain-specific modifications of the dominant phosphoglycan (PG) repeat units. For the “selective” fly Phlebotomus papatasi PpapJ, side chain galactosyl-modifications (scGal) of PG repeats play key roles in parasite binding. We probed the specificity and properties of this scGal-LPG PAMP (Pathogen Associated Molecular Pattern) through studies of natural isolates exhibiting a wide range of galactosylation patterns, and of a panel of isogenic L. major engineered to express similar scGal-LPG diversity by transfection of SCG-encoded β1,3-galactosyltransferases with different activities. Surprisingly, both ‘poly-scGal’ and ‘null-scGal’ lines survived poorly relative to PpapJ-sympatric L. major FV1 and other ‘mono-scGal’ lines. However, survival of all lines was equivalent in P. duboscqi, which naturally transmit L. major strains bearing ‘null-scGal’-LPG PAMPs. We then asked whether scGal-LPG-mediated interactions were sufficient for PpapJ midgut survival by engineering Leishmania donovani, which normally express unsubstituted LPG, to express a ‘PpapJ-optimal’ scGal-LPG PAMP. Unexpectedly, these “L. major FV1-cloaked” L. donovani-SCG lines remained unable to survive within PpapJ flies. These studies establish that midgut survival of L. major in PpapJ flies is exquisitely sensitive to the scGal-LPG PAMP, requiring a specific ‘mono-scGal’ pattern. However, failure of ‘mono-scGal’ L. donovani-SCG lines to survive in selective PpapJ flies suggests a requirement for an additional, as yet unidentified L. major-specific parasite factor(s). The interplay of the LPG PAMP and additional factor(s) with sand fly midgut receptors may determine whether a given sand fly host is “selective” or “permissive”, with important consequences to both disease transmission and the natural co-evolution of sand flies and Leishmania.

Phlebotomine sand flies are tiny blood-feeding insects that transmit Leishmania protozoan parasites, which cause diseases afflicting millions of people. The world-wide distribution of Leishmania is determined by the availability of transmission-competent vectors. In the laboratory, some vectors support many different Leishmania, while others are highly restricted. This is best exemplified by P. papatasi, which transmit only L. major despite a wide distribution in regions endemic for many Leishmania species. P. papatasi “selectivity” can be reproduced experimentally, and has been attributed to β1,3-linked galactose side chains decorating the abundant L. major surface lipophosphoglycan (LPG) adhesin, which mediate parasite attachment to the P. papatasi midgut to prevent elimination when the digested blood meal is excreted. As geographically diverse L. major display very different LPG galactosylation patterns (n = 0 - 8 βGals/side chain), we explored the consequences of this pattern diversity to survival in P. papatasi. Using natural isolates and L. major lines engineered to express a wide range of LPG galactosylation patterns, we showed L. major survival in P. papatasi PpapJ flies was optimized by expression of highly modified ‘mono-galactosylated’ LPG and extremely sensitive to LPG side chain length. Surprisingly, L. donovani lines engineered to express a “PpapJ-optimal” LPG mono-galactosylation pattern did not survive in PpapJ flies, suggesting that additional interactions are required. These studies reveal the fine specificity of Leishmania - sand fly interactions, and the nature of species- and strain-specific parasite molecules that have co-evolved to take advantage of midgut receptors specific to available sand fly vectors.

The human pathogen Leishmania donovani secretes a histidine acid phosphatase activity that is resistant to proteolytic degradation

Promastigotes of all pathogenic Leishmania species secrete acid phosphatase (SAcP) activity during their growth in vitro. It has been suggested that this enzyme may play a role in the survival of the parasite within its sandfly-vector host. To carry out such functions, SAcP would have to be relatively resistant to endogenous sandfly gut-proteases. Therefore, the current study was undertaken to ascertain whether L. donovani SAcP activity was affected by treatment with various proteases. Native L. donovani SAcP was treated with a variety of serine-, thiol-, metallo- and mixed-proteases and subsequently assayed for enzymatic activity. Of the eleven proteases tested, only bromelain and subtilisin treatments caused a pronounced reduction in SAcP activity. Treatment of SAcP with seven out of the remaining nine proteases, resulted in an overall enhancement in SAcP enzymatic activity ranging from approximately 10% (e.g. with trypsin) to > or = 90% (e.g. with ficin). The resistance of the Leishmania SAcP to various proteases may prolong its functional life within the sandfly gut and help to facilitate parasite infection in this host.

An in vitro system for developmental and genetic studies of Leishmania donovani phosphoglycans

Glycoconjugates have been shown to play important roles in Leishmania development. However, the ability to study these molecules and other processes would benefit greatly from improved methods for genetic manipulation and analysis of the amastigote stage. This is especially challenging for L. donovani, the agent of the most severe form of leishmaniasis, which can rapidly lose virulence during in vitro culture. Here we report on a clonal subline of an L. donovani 1S2D (LdBob or LdB), which differentiates readily from promastigotes to amastigotes in axenic culture, and maintains this ability during extended parasite cultivation in vitro. This derivative can be plated and transfected efficiently while grown as promastigotes or amastigotes. Importantly, LdB maintains the ability to differentiate while undergoing genetic alterations required for creation of gene knockouts and complemented lines. Like virulent L. donovani, LdB exhibits down-regulation of lipophosphoglycan (LPG) synthesis and up-regulation of A2 protein synthesis in amastigotes. We showed that knockouts of LPG2, encoding a Golgi GDP-mannose transporter, eliminated phosphoglycan synthesis in LdB axenic amastigotes. These and other data suggest that LdB axenic amastigotes will be generally useful as a differentiation model in studies of gene expression, virulence, glycoconjugate function and drug susceptibility in L. donovani.

Secretory pathway of trypanosomatid parasites

The Trypanosomatidae comprise a large group of parasitic protozoa, some of which cause important diseases in humans. These include Trypanosoma brucei (the causative agent of African sleeping sickness and nagana in cattle), Trypanosoma cruzi (the causative agent of Chagas' disease in Central and South America), and Leishmania spp. (the causative agent of visceral and [muco]cutaneous leishmaniasis throughout the tropics and subtropics). The cell surfaces of these parasites are covered in complex protein- or carbohydrate-rich coats that are required for parasite survival and infectivity in their respective insect vectors and mammalian hosts. These molecules are assembled in the secretory pathway. Recent advances in the genetic manipulation of these parasites as well as progress with the parasite genome projects has greatly advanced our understanding of processes that underlie secretory transport in trypanosomatids. This article provides an overview of the organization of the trypanosomatid secretory pathway and connections that exist with endocytic organelles and multiple lytic and storage vacuoles. A number of the molecular components that are required for vesicular transport have been identified, as have some of the sorting signals that direct proteins to the cell surface or organelles in the endosome-vacuole system. Finally, the subcellular organization of the major glycosylation pathways in these parasites is reviewed. Studies on these highly divergent eukaryotes provide important insights into the molecular processes underlying secretory transport that arose very early in eukaryotic evolution. They also reveal unusual or novel aspects of secretory transport and protein glycosylation that may be exploited in developing new antiparasite drugs.

Symbiosis therapy: the potential of using human protozoa for molecular therapy

The concept of symbiosis is proposed as a disease therapy model. It is hypothesized that protozoa that live naturally in human tissues can be genetically modified for the production and delivery of therapeutic proteins. Approximately 30 identified species of protozoa live in a variety of human tissues, both intracellularly and extracellularly. Leishmania, one species of human protozoa, has been genetically altered for conditional auxotrophy and has shown no pathology in both mouse and nonhuman primate safety tests. Several species of protozoa have been transfected with a variety of genes and have successfully manufactured active foreign proteins. Protozoa have biochemical mechanisms to glycosylate proteins. Human protozoa have evolved sophisticated mechanisms for evading immune rejection and can sometimes persist for the lifetime of the host. Symbiosis therapy does not involve genetic alteration of the host and is potentially fully reversible. Research on treating genetic diseases is currently ongoing. For example, there is a group of more than 40 genetic diseases, lysosomal storage diseases, which result from defects in lysosomal enzymes primarily in macrophages. Leishmania specifically targets the lysosomal compartment of the macrophage and therefore may be the optimal vector for treatment of many of these diseases.

Proteophosphoglycans of Leishmania

Proteophosphoglycans are an expanding family of highly glycosylated Leishmania proteins with many unusual and some unique structural features. The novel protein-glycan linkage in proteophosphoglycans - phosphoglycosylation of Ser by lipophosphoglycan-like structures - emerges as a major form of protein glycosylation in Leishmania. Here, Thomas Ilg reviews the chemical structure, the ultrastructure, the genes and the potential functions of different members of this novel family of parasite glycoproteins.

Structurally conserved soluble acid phosphatases are synthesized and released by Leishmania major promastigotes

Previously it was reported that promastigotes of virtually all pathogenic Leishmania species, except Leishmania major, release a structurally conserved soluble acid phosphatase (AcP) activity during their growth in vitro (P. S. Doyle and D. M. Dwyer, Exp. Parasitol. 77, 435-444 1993). In the current study we used a highly sensitive fluorogenic detection method to demonstrate that soluble AcPs were in fact produced by promastigotes of several different strains of L. major. These L. major AcP activities were readily immunoprecipitated with a rabbit antibody previously generated against the L. donovani AcP. Results of metabolic labeling and immunoprecipitations demonstrated that AcPs produced by the L. majors strains examined had an apparent molecular mass of approximately 77 kDa. Results of Southern hybridization analysis with an L. donovani AcP gene probe showed that the AcP gene loci were conserved in the L. major strains examined. Taken together, these results indicate that the AcP enzyme has been structurally and functionally conserved throughout the evolution of pathogenic species of Leishmania. Such conservation suggests that the AcPs play a functional role in the growth and survival of this group of important human pathogens.