RPA-1 from Leishmania amazonensis (LaRPA-1) structurally differs from other eukaryote RPA-1 and interacts with telomeric DNA via its N-terminal OB-fold domain

Replication protein A-1 (RPA-1) is a single-stranded DNA-binding protein involved in DNA metabolism. We previously demonstrated the interaction between LaRPA-1 and telomeric DNA. Here, we expressed and purified truncated mutants of LaRPA-1 and used circular dichroism measurements and molecular dynamics simulations to demonstrate that the tertiary structure of LaRPA-1 differs from human and yeast RPA-1. LaRPA-1 interacts with telomeric ssDNA via its N-terminal OB-fold domain, whereas RPA from higher eukaryotes show different binding modes to ssDNA. Our results show that LaRPA-1 is evolutionary distinct from other RPA-1 proteins and can potentially be used for targeting trypanosomatid telomeres.     

A serine protease from a detergent-soluble extract of Leishmania (Leishmania) amazonensis

Proteases mediate important crucial functions in parasitic diseases, and their characterization contributes to the understanding of host-parasite interaction. A serine protease was purified about 43-fold with a total recovery of 60% from a detergent-soluble extract of promastigotes of Leishmania amazonensis. The purification procedures included aprotinin-agarose affinity chromatography and gel filtration high performance liquid chromatography. The molecular mass of active enzyme was 110 kDa by native gel filtration HPLC and by SDS-PAGE gelatin under non-reducing conditions. Under conditions of reduction using SDS-PAGE gelatin analyses the activity of enzyme was observed in two proteins of 60 and 45 kDa, suggesting that the enzyme may be considered as a dimer. The Leishmania protease was not glycosylated, and its isoelectric point (pI) was around 4.8. The maximal protease activity was at pH 7.0 and 28 degrees C, using a-N-o-tosyl-L-arginyl-methyl ester (L-TAME) as substrate. Assays of thermal stability indicated that this enzyme was totally denatured after pre-treatment at 42 degrees C for 12 min and preserved only 20% of its activity after pre-treatment at 37 degrees C for 24 h, in the absence of substrate. Hemoglobin, bovine serum albumin (BSA), ovalbumin and gelatin were hydrolyzed by Leishmania protease. Inhibition studies indicated that the enzyme belonged to a serine protease class because of a significant impediment by serine protease inhibitors such as benzamidine, aprotinin, and antipain. The activity of the present serine protease is negatively modulated by calcium and zinc and positively modulated by manganese ions. This is the first study that reports the purification of a protease from a detergent-soluble extract of Leishmania species.     

Active Transport of Glutamate in Leishmania (Leishmania) amazonensis

ABSTRACT. Leishmania spp. are the causative agents of leishmaniasis, a complex of diseases with a broad spectrum of clinical manifestations. Leishmania (Leishmania) amazonensis is a main etiological agent of diffuse cutaneous leishmaniasis. Leishmania spp., as other trypanosomatids, possess a metabolism based significantly on the consumption of amino acids. However, the transport of amino acids in these organisms remains poorly understood with few exceptions. Glutamate transport is an important biological process in many organisms. In the present work, the transport of glutamate is characterized. This process is performed by a single kinetic system (K_m=0.59±0.04 mM, V_max=0.123±0.003 nmol/min per 20 × 10⁶ cells) showing an energy of activation of 52.38±4.7 kJ/mol and was shown to be partially inhibited by analogues, such as glutamine, aspartate, α‐ketoglutarate and oxaloacetate, methionine, and alanine. The transport activity was sensitive to the extracellular concentration of H⁺ but not to Na⁺ or K⁺. However, unlike other amino acid transporters presently characterized, the treatment with specific ionophores confirmed the participation of a K⁺, and not H⁺ membrane gradient in the transport process.     

Leishmania (Leishmania) amazonensis: purification and characterization of a promastigote serine protease

Pathogenic protozoan proteases play crucial roles in the host-parasite interaction, and its characterization contributes to the understanding of protozoan disease mechanisms. A Leishmania amazonensis promastigote protease was purified 36-fold, using aprotinin-agarose affinity chromatography and gel filtration high performance liquid chromatography, yielding a total recovery of 49%. The molecular mass of active enzyme obtained from native gel filtration HPLC and SDS-PAGE under conditions of reduction and non-reduction was 68 kDa, suggesting that the enzyme may exist as a monomer. The protease isoelectric point (pI) was around 4.45 and, as demonstrated by deglycosylation assay, it did not have any carbohydrate content. The optimal pH and temperature of the enzyme were 8.0 and 28 degrees C, respectively, determined using alpha-N-rho-tosyl-L-arginyl-methyl ester (L-TAME) as substrate. Assays of thermal stability indicated that 50% of the enzymatic activity was preserved after 4 min of pre-treatment at 42 degrees C and after 24 h of pre-treatment at 37 degrees C, both in the absence of substrate. Hemoglobin, bovine serum albumin (BSA), ovalbumin, and both gelatin and peptide substrates containing arginine in ester bound were hydrolyzed by 68 kDa protease. The insulin beta-chain was also hydrolyzed by the protease, and four peptidic bonds (L11-V12, E13-A14, L15-Y16, and Y16-L17) were susceptible to the 68-kDa protease action. Inhibition studies suggested that the enzyme belonged to a serine protease class inhibited by calcium ions and activated by manganese ions. These findings demonstrate that the L. amazonensis 68-kDa serine protease differs from those of other protozoan parasites.     

Identification and characterization of a putative telomere end-binding protein from Tetrahymena thermophila.

Telomeric DNA of Tetrahymena thermophila consists of a long stretch of (TTGGGG)n double-stranded repeats with a single-stranded (TTGGGG)2 3' overhang at the end of the chromosome. We have identified and characterized a protein that specifically binds to a synthetic telomeric substrate consisting of duplex DNA and the 3' telomeric repeat overhang. This protein is called TEP (telomere end-binding protein). A change from G to A in the third position of the TTGGGG overhang repeat converts the substrate to a human telomere analog and reduces the binding affinity approximately threefold. Changing two G's to C's in the TTGGGG repeats totally abolishes binding. However, permutation of the Tetrahymena repeat sequence has only a minor effect on binding. A duplex structure adjacent to the 3' overhang is required for binding, although the duplex need not contain telomeric repeats. TEP does not bind to G-quartet DNA, which is formed by many G-rich sequences. TEP has a greatly reduced affinity for RNA substrates. The copy number of TEP is at least 2 x 10(4) per cell, and it is present under different conditions of cell growth and development, although its level varies. UV cross-linking experiments show that TEP has an apparent molecular mass of approximately 65 kDa. Unlike other telomere end-binding proteins, TEP is sensitive to high salt concentrations.     

In vitro and in vivo activity of a palladacycle complex on Leishmania (Leishmania) amazonensis

Background

Antitumor cyclopalladated complexes with low toxicity to laboratory animals have shown leishmanicidal effect. These findings stimulated us to test the leishmanicidal property of one palladacycle compound called DPPE 1.2 on Leishmania (Leishmania) amazonensis, an agent of simple and diffuse forms of cutaneous leishmaniasis in the Amazon region, Brazil.

Methodology/Principal Findings

Promastigotes of L. (L.) amazonensis and infected bone marrow-derived macrophages were treated with different concentrations of DPPE 1.2. In in vivo assays foot lesions of L. (L.) amazonensis-infected BALB/c mice were injected subcutaneously with DPPE 1.2 and control animals received either Glucantime or PBS. The effect of DPPE 1.2 on cathepsin B activity of L. (L.) amazonensis amastigotes was assayed spectrofluorometrically by use of fluorogenic substrates. The main findings were: 1) axenic L. (L.) amazonensis promastigotes were destroyed by nanomolar concentrations of DPPE 1.2 (IC50 = 2.13 nM); 2) intracellular parasites were killed by DPPE 1.2 (IC50 = 128.35 nM), and the drug displayed 10-fold less toxicity to macrophages (CC50 = 1,267 nM); 3) one month after intralesional injection of DPPE 1.2 infected BALB/c mice showed a significant decrease of foot lesion size and a reduction of 97% of parasite burdens when compared to controls that received PBS; 4) DPPE 1.2 inhibited the cysteine protease activity of L. (L.) amazonensis amastigotes and more significantly the cathepsin B activity.

Conclusions/Significance

The present results demonstrated that DPPE 1.2 can destroy L. (L.) amazonensis in vitro and in vivo at concentrations that are non toxic to the host. We believe these findings support the potential use of DPPE 1.2 as an alternative choice for the chemotherapy of leishmaniasis.     

Dimeric structure of the Oxytricha nova telomere end-binding protein alpha-subunit bound to ssDNA

Telomeres are the specialized protein--DNA complexes that cap and protect the ends of linear eukaryotic chromosomes. The extreme 3' end of the telomeric DNA in Oxytricha nova is bound by a two-subunit sequence-specific and 3' end-specific protein called the telomere end-binding protein (OnTEBP). Here we describe the crystal structure of the alpha-subunit of OnTEBP in complex with T4G4 single-stranded telomeric DNA. This structure shows an (alpha--ssDNA)2 homodimer with a large approximately 7,000 A2 protein--protein interface in which the domains of alpha are rearranged extensively from their positions in the structure of an alpha--beta--ssDNA ternary complex. The (alpha--ssDNA)2 complex can bind two telomeres on opposite sides of the dimer and, thus, acts as a protein mediator of telomere--telomere associations. The structures of the (alpha--ssDNA)2 dimer presented here and the previously described alpha--beta--ssDNA complex demonstrate that OnTEBP forms multiple telomeric complexes that potentially mediate the assembly and disassembly of higher order telomeric structures.     

Genomic organization of telomeric and subtelomeric sequences of Leishmania (Leishmania) amazonensis

Telomeres are DNA-protein complexes that protect linear chromosomes from degradation and fusions. Telomeric DNA is repetitive and G-rich, and protrudes towards the end of the chromosomes as 3'G-overhangs. In Leishmania spp., sequences adjacent to telomeres comprise the Leishmania conserved telomere associated sequences (LCTAS) that are around 100 bp long and contain two conserved sequence elements (CSB1 and CSB2), in addition to non-conserved sequences. The aim of this work was to study the genomic organization of Leishmania (Leishmania) amazonensis telomeric/subtelomeric sequences. Leishmania amazonensis chromosomes were separated in a single Pulsed Field Gel Electrophoresis (PFGE) gel as 25 ethidium bromide-stained bands. All of the bands hybridized with the telomeric probe (5'-TTAGGG-3')3 and with probes generated from the conserved subtelomeric elements (CSB1, CSB2). Terminal restriction fragments (TRF) of L. amazonensis chromosomes were analyzed by hybridizing restriction digested genomic DNA and chromosomal DNA separated in 2D-PFGE with the telomeric probe. The L. amazonensis TRF was estimated to be approximately 3.3 kb long and the telomeres were polymorphic and ranged in size from 0.2 to 1.0 kb. Afa I restriction sites within the conserved CSB1 elements released the telomeres from the rest of the chromosome. Bal 31-sensitive analysis confirmed the presence of terminal Afa I restriction sites and served to differentiate telomeric fragments from interstitial internal sequences. The size of the L. amazonensis 3' G-overhang was estimated by non-denaturing Southern blotting to be approximately 12 nt long. Using similar approaches, the subtelomeric domains CSB1 and CSB2 were found to be present in a low copy number compared to telomeres and were organized in blocks of 0.3-1.5 kb flanked by Hinf I and Hae III restriction sites. A model for the organization of L. amazonensis chromosomal ends is provided.     

Genomic organisation and transcription characterisation of the gene encoding Leishmania (Leishmania) amazonensis arginase and its protein structure prediction

The genomic organisation of the gene encoding Leishmania (Leishmania) amazonensis arginase as well as its flanking regions were characterised. The size of the transcribed RNA was determined, allowing us to map the genomic sites signalling for RNA trans-splicing and putative polyadenylation regions. The general organisation was compared with genes encoding other proteins already described in organisms of the Trypanosomatid family. The complete nucleotide sequence of the arginase open reading frame was obtained and the three-dimensional structure of the enzyme was inferred by a computational analysis of the deduced amino acid sequence, based on the established crystal structure described for Rattus norvergicus arginase. The human liver arginase sequence was analysed in the same way and the comparison of the presumed structure of both the Leishmania and human enzymes identified some differences that may be exploited in chemotherapeutic studies.     

Heat shock induction of apoptosis in promastigotes of the unicellular organism Leishmania (Leishmania) amazonensis

Apoptosis and/or programmed cell death have been described in examples ranging from fungi to man as gene-regulated processes with roles in cell and tissue physiopathology. These processes require the operation of an intercellular communicating network able to deliver alternative signals for cells with different fates and is thus considered a prerogative of multicellular organisms. Promastigotes from Leishmania (Leishmania) amazonensis, when shifted from their optimal in vitro growth temperature (22°C) to the temperature of the mammalian host (37°C), die by a calcium-modulated mechanism. More parasites die in the presence of this ion than in its absence, as detected by a colorimetric assay based on the activity of mitochondrial and cytoplasmic dehydrogenases which measures cell death, independently of the process by which it occurs. A heat shock, unable to induce detectable parasite death (34°C for 1 h), is able to significantly raise the concentration of intracellular free calcium in these cells. Heat-shocked parasites present ultrastructural and molecular features characteristic of cells dying by apoptosis. Morphological changes, observed only in the presence of calcium, are mainly nuclear. Cytoplasmic organelles are preserved. Heat shock is also able to induce DNA cleavage into an oligonucleosomal ladder detected in agarose gels by ethidium bromide staining and autoradiography of [α³²P]ddATP-labeled fragments. These results indicate that death by apoptosis is not exclusive of multicellular organisms. © 1996 Wiley-Liss, Inc.     

Crystal structure of the amino-terminal microtubule-binding domain of end-binding protein 1 (EB1)

The end-binding protein 1 (EB1) family is a highly conserved group of proteins that localizes to the plus-ends of microtubules. EB1 has been shown to play an important role in regulating microtubule dynamics and chromosome segregation, but its regulation mechanism is poorly understood. We have determined the 1.45-A resolution crystal structure of the amino-terminal domain of EB1, which is essential for microtubule binding, and show that it forms a calponin homology (CH) domain fold that is found in many proteins involved in the actin cytoskeleton. The functional CH domain for actin binding is a tandem pair, whereas EB1 is the first example of a single CH domain that can associate with the microtubule filament. Although our biochemical study shows that microtubule binding of EB1 is electrostatic in part, our mutational analysis suggests that the hydrophobic network, which is partially exposed in our crystal structure, is also important for the association. We propose that, like other actin-binding CH domains, EB1 employs the hydrophobic interaction to bind to microtubules.     

Experimental infection with Leishmania (Viannia) braziliensis and Leishmania (Leishmania) amazonensis in the marmoset, Callithrix penicillata (Primates:Callithricidae)

Fourteen marmosets (Callithrix penicillata) were inoculated intradermally with promastigotes and/or amastigotes of Leishmania (Viannia) braziliensis (L. (V) b.) strains MHOM/BR/83/LTB-300 MHOM/BR/85/LTB-12 MHOM/BR/81/LTB-179 and MHOM/BR/82/LTB-250. The evolution of subsequent lesions was studied for 15 to 75 weeks post-inoculation (PI). All but 3 of the L. (V) b. injected marmosets developed a cutaneous lesion at the point of inoculation after 3 to 9 weeks, characterized by the appearance of subcutaneous nodules containing parasites. Parasites were isolated by culture (Difco Blood Agar) from all 11 positive animals. The maximum size of the lesions was variable and ranged between 37 mm2 to 107 mm2. Ulceration of primary nodules became evident after 3 to 12 weeks in all infected marmosets, but was faster and larger in 5 of the 11 animals. The active lesions persisted in 9 out of 11 Callithrix until the end of the observation period, which varied from 15-75 weeks. In 3 animals spontaneous healing of their lesions (13 to 25 weeks, PI) was observed but with cryptic parasitism. In another 2 infected animals there was regression followed by reactivation of the cutaneous lesions. The appearance of smaller satellite lesions adjacent to primary ones, as well as metastatic lesions to the ear lobes, were documented in 2 animals. Promastigotes of L. (Leishmania) amazonensis (L. (L) a.) MHOM/BR/77/LTB-16 were inoculated in 1 marmoset. This animal remained chronically infected for 6 months and the lesion developed in a similar manner to L. (V) b. infected marmosets. No significant differences in clinical and parasitological behaviour were observed between promastigote or amastigote derived infections of the 2 species.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structural and functional analysis of the LaMDR1 multidrug resistance gene in Leishmania amazonensis

We determined primary sequences of the LaMDR1 gene in Leishmania amazonensis, a protozoan parasite that causes cutaneous leishmaniasis. The longest open reading frame encodes 1341 amino acids for a protein consisting of two similar halves, each containing six putative transmembrane domains and one ATP-binding domain. The protein has no potential N-glycosylation sites at the extracellular region. The LaMDR1 protein was 91 and 78% identical to the closely related ldmdr1 in L. donovani and lemdr1 in L. enriettii, respectively, revealing less conservation in the C-terminal than in the N-terminal transmembrane domains. Transfection of LaMDR1 conferred a multidrug resistance phenotype to wild-type promastigotes, which exhibited a significant level of resistance to vinblastine, doxorubicin, and actinomycin D, but not to puromycin and colchicine. This drug specificity of LaMDR1 was overlapping with but distinct from that of ldmdr1, suggesting functional diversity of MDR1 proteins among different Leishmania species.     

Analysis and chromosomal mapping of Leishmania (Leishmania) amazonensis amastigote expressed sequence tags

The characterization of expressed sequence tags (ESTs) generated from a cDNA library of Leishmania (Leishmania) amazonensis amastigotes is described. The sequencing of 93 clones generated new L. (L.) amazonensis ESTs from which 32% are not related to any other sequences in database and 68% presented significant similarities to known genes. The chromosome localization of some L. (L.) amazonensis ESTs was also determined in L. (L.) amazonensis and L. (L.) major. The characterization of these ESTs is suitable for the genome physical mapping, as well as for the identification of genes encoding cysteine proteinases implicated with protective immune responses in leishmaniasis.     

Effect of the Synadenium carinatum latex lectin (ScLL) on Leishmania (Leishmania) amazonensis infection in murine macrophages

Antiparasitic effect of a lectin isolated from Synadenium carinatum latex (ScLL) was evaluated against Leishmania (Leishmania) amazonensis promastigotes/amastigotes. Pretreatment of murine inflammatory peritoneal macrophages with ScLL reduced by 65.5% the association index of macrophages and L. (L) amazonensis promastigotes. Expression of cytokines (IL-12, IL-1 and TNF-α) was detected in infected macrophages pretreated with ScLL (10 μg/mL). ScLL also reduced the growth of L. (L) amazonensis amastigote intracellular forms, showing no in vitro cytotoxic effects in mammalian host cells. ScLL treatment in infected murine inflammatory peritoneal macrophages did not induce nitric oxide production, suggesting that a nitric oxide independent pathway is activated to decrease the number of intracellular Leishmania.     

Action of pentoxifylline on experimental cutaneous leishmaniasis due to Leishmania (Leishmania) amazonensis

In the animal model of leishmaniasis caused by Leishmania (Leishmania) amazonensis there is a complex mechanism of the host-parasite interaction. The present study was performed to interfere with the inflammatory reaction to the parasites, through immune modulation. Female C5BL/6 isogenic mice were used, some of which were inoculated on the right ear and others on the right footpad with 3.10(6) stationary phase promastigotes of the MHOM/BR/PH8 strain of L. (L.) amazonensis, and were allocated in three groups: the first received pentoxifylline 8mg/kg every 12 h, since the first day; the second one received the same dose since the 40th day of infection and a control group that did not receive any treatment. All the ears excised were analyzed to determine the variation in weight between both ears and for histopathological analyses. A quantification of the parasites was done using the limiting dilution assay. A significant reduction of the number of parasites, was observed among the animals treated which had an accordingly significant reduction on the weight of the ears. Pentoxifylline reduced the macrophages propensity to vacuolation and induced a more effective destruction of the parasites by these cells. Moreover, the group that began the treatment later did not show the same effectiveness.     

Correlation of meta 1 expression with culture stage, cell morphology and infectivity in Leishmania (Leishmania) amazonensis promastigotes

The parasitic protozoan Leishmania (Leishmania) amazonensis alternates between mammalian and insect hosts. In the insect host, the parasites proliferate as procyclic promastigotes and then differentiate into metacyclic infective forms. The meta 1 gene is preferentially expressed during metacyclogenesis. Meta 1 expression profile determination along parasite growth curves revealed that the meta 1 mRNA level peaked at the early stationary phase then decreased to an intermediate level. No correlation was observed between meta 1 expression and infectivity. Conversely, infectivity correlated with the increase of apoptotic cells in the late stationary phase.     

Leishmania (Leishmania) amazonensis: experimental cutaneous leishmaniasis associated with systemic amyloidosis in mice

We infected Swiss and C57BL/6 female mice in the left hind footpad with 10⁴Leishmania (L.) amazonensis promastigotes in stationary phase. The macroscopic examination showed a nodular non-ulcerated lesion at the site of inoculation and hepatic and spleenic enlargement. Histopathologically, the primary lesion showed an extensive liquefactive necrosis and inflammatory infiltrate, mainly consisting of macrophages filled with amastigotes, and rare lymphocytes. The inflammatory reaction in liver, spleen and kidney showed amyloid deposits. Additionally, C57BL/6 had accentuated amyloidosis in both ovarian cortical and medullar region and inflammatory infiltrates in the pancreas and adrenal gland.     

Subcellular localization of an intracellular serine protease of 68 kDa in Leishmania (Leishmania) amazonensis promastigotes

Here we report the subcellular localization of an intracellular serine protease of 68 kDa in axenic promastigotes of Leishmania (Leishmania) amazonensis, using subcellular fractionation, enzymatic assays, immunoblotting, and immunocytochemistry. All fractions were evaluated by transmission electron microscopy and the serine protease activity was measured during the cell fractionation procedure using alpha-N-r-tosyl-L-arginine methyl ester (L-TAME) as substrate, phenylmethylsulphone fluoride (PMSF) and L-1-tosylamino-2-phenylethylchloromethylketone (TPCK) as specific inhibitors. The enzymatic activity was detected mainly in a membranous vesicular fraction (6.5-fold enrichment relative to the whole homogenate), but also in a crude plasma membrane fraction (2.0-fold). Analysis by SDS-PAGE gelatin under reducing conditions demonstrated that the major proteolytic activity was found in a 68 kDa protein in all fractions studied. A protein with identical molecular weight was also recognized in immunoblots by a polyclonal antibody against serine protease (anti-SP), with higher immunoreactivity in the vesicular fraction. Electron microscopic immunolocalization using the same polyclonal antibody showed the enzyme present at the cell surface, as well as in cytoplasmic membranous compartments of the parasite. Our findings indicate that the internal location of this serine protease in L. amazonensis is mainly restricted to the membranes of intracellular compartments resembling endocytic/exocytic elements.     

Identification of three proteins that associate in vitro with the Leishmania (Leishmania) amazonensis G-rich telomeric strand.

The chromosomal ends of Leishmania (Leishmania) amazonensis contain conserved 5'-TTAGGG-3' telomeric repeats. Protein complexes that associate in vitro with these DNA sequences, Leishmania amazonensis G-strand telomeric protein (LaGT1-3), were identified and characterized by electrophoretic mobility shift assays and UV cross-linking using protein fractions purified from S100 and nuclear extracts. The three complexes did not form (a) with double-stranded DNA and the C-rich telomeric strand, (b) in competition assays using specific telomeric DNA oligonucleotides, or (c) after pretreatment with proteinase K. LaGT1 was the most specific and did not bind a Tetrahymena telomeric sequence. All three LaGTs associated with an RNA sequence cognate to the telomeric G-rich strand and a complex similar to LaGT1 is formed with a double-stranded DNA bearing a 3' G-overhang tail. The protein components of LaGT2 and LaGT3 were purified by affinity chromatography and identified, after renaturation, as approximately 35 and approximately 52 kDa bands, respectively. The 相似文献