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Modeling of the N-Glycosylated Transferrin Receptor Suggests How Transferrin Binding Can Occur within the Surface Coat of Trypanosoma brucei  [PDF]
Angela Mehlert,Mark R. Wormald,Michael A. J. Ferguson
PLOS Pathogens , 2012, DOI: 10.1371/journal.ppat.1002618
Abstract: The transferrin receptor of bloodstream form Trypanosoma brucei is a heterodimer encoded by expression site associated genes 6 and 7. This low-abundance glycoprotein with a single glycosylphosphatidylinositol membrane anchor and eight potential N-glycosylation sites is located in the flagellar pocket. The receptor is essential for the parasite, providing its only source of iron by scavenging host transferrin from the bloodstream. Here, we demonstrate that both receptor subunits contain endoglycosidase H-sensitive and endoglycosidase H-resistant N-glycans. Lectin blotting of the purified receptor and structural analysis of the released N-glycans revealed oligomannose and paucimannose structures but, contrary to previous suggestions, no poly-N-acetyllactosamine structures were found. Overlay experiments suggest that the receptor can bind to other trypanosome glycoproteins, which may explain this discrepancy. Nevertheless, these data suggest that a current model, in which poly-N-acetyllactosamine glycans are directly involved in receptor-mediated endocytosis in bloodstream form Trypanosoma brucei, should be revised. Sequential endoglycosidase H and peptide-N-glycosidase F treatment, followed by tryptic peptide analysis, allowed the mapping of oligomannose and paucimannose structures to four of the receptor N-glycosylation sites. These results are discussed with respect to the current model for protein N-glycosylation in the parasite. Finally, the glycosylation data allowed the creation of a molecular model for the parasite transferrin receptor. This model, when placed in the context of a model for the dense variant surface glycoprotein coat in which it is embedded, suggests that receptor N-glycosylation may play an important role in providing sufficient space for the approach and binding of transferrin to the receptor, without significantly disrupting the continuity of the protective variant surface glycoprotein coat.
Heme-Induced ROS in Trypanosoma Cruzi Activates CaMKII-Like That Triggers Epimastigote Proliferation. One Helpful Effect of ROS  [PDF]
Natália Pereira de Almeida Nogueira, Cintia Fernandes de Souza, Francis Monique de Souza Saraiva, Pedro Elias Sultano, Sergio Ranto Dalmau, Roberta Eitler Bruno, Renata de Lima Sales Gon?alves, Gustavo Augusto Travassos Laranja, Luís Henrique Monteiro Leal, Marsen Garcia Pinto Coelho, Claudio A. Masuda, Marcus F. Oliveira, Marcia Cristina Paes
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0025935
Abstract: Heme is a ubiquitous molecule that has a number of physiological roles. The toxic effects of this molecule have been demonstrated in various models, based on both its pro-oxidant nature and through a detergent mechanism. It is estimated that about 10 mM of heme is released during blood digestion in the blood-sucking bug's midgut. The parasite Trypanosoma cruzi, the agent of Chagas' disease, proliferates in the midgut of the insect vector; however, heme metabolism in trypanosomatids remains to be elucidated. Here we provide a mechanistic explanation for the proliferative effects of heme on trypanosomatids. Heme, but not other porphyrins, induced T. cruzi proliferation, and this phenomenon was accompanied by a marked increase in reactive oxygen species (ROS) formation in epimastigotes when monitored by ROS-sensitive fluorescent probes. Heme-induced ROS production was time-and concentration-dependent. In addition, lipid peroxidation and the formation of 4-hydroxy-2-nonenal (4-HNE) adducts with parasite proteins were increased in epimastigotes in the presence of heme. Conversely, the antioxidants urate and GSH reversed the heme-induced ROS. Urate also decreased parasite proliferation. Among several protein kinase inhibitors tested only specific inhibitors of CaMKII, KN93 and Myr-AIP, were able to abolish heme-induced ROS formation in epimastigotes leading to parasite growth impairment. Taken together, these data provide new insight into T. cruzi- insect vector interactions: heme, a molecule from the blood digestion, triggers epimastigote proliferation through a redox-sensitive signalling mechanism.
In vitro Anti-epimastigote Activity of some Iranian Medicinal Plants
Soodabeh Saeidnia,Ahmad Reza Gohari,Fumiyuki Kiuchi,Gisho Honda
Iranian Journal of Pharmaceutical Research , 2005,
Abstract: Some medicinal plants are a potential source of new drugs, in order to improve the treatment of Chagas disease whose treatment is still a challenge. In this study, the in vitro anti-epimastigote activity of certain fractions of Achillea biebersteinii, A. millefolium, Satureja mutica and S. macrantha was evaluated. Diethyl ether fractions of Achillea species and acetone fractions of Satureja species were the most active fractions (MLC=12.5 μg/ml) against theepimastigotes of Trypanosoma cruzi, the ethiological agent causing Chagas disease. The trypanocidal activity seems to be decreased by fractionation, using MeOH and water as the solvents. The results obtained from biological assay revealed that Achillea and Satureja species could be a source of active trypanocidal compounds.
Alkaline soluble Trypanosoma cruzi epimastigote antigen (ASEA) applied to dot-ELISA
Lissaldo, Ana Maria;Hoshino-Shimizu, Sumie;Umezawa, Eufrosina Setsu;Stolf, Anna Maria Simonsen;
Revista do Instituto de Medicina Tropical de S?o Paulo , 1994, DOI: 10.1590/S0036-46651994000200012
Abstract: the alkaline soluble trypanosoma cruzi epimastigote antigen (asea) was assessed in dot-elisa for the diagnosis of chagas' disease. serum samples (355) from chagasic and non-chagasic patients were studied, and igg antibodies to asea were found in all patients with chronic chagas' disease. in non-chagasic patients 95.6% were negative, except for those with leishmaniasis (visceral and mucocutaneous), and some patients from control group reacted in low titers. the data indicate that dot-elisa using asea is suitable for seroepidemiologic surveys to be employed in endemic areas for chagas' disease.
Chagas' disease: IgA, IgM and IgG antibodies to T. cruzi amastigote, trypomastigote and epimastigote antigens in acute and in different chronic forms of the disease
Primavera, Kátia S. C.;Umezawa, Eufrosina S.;Peres, Benedito Anselmo;Camargo, Mário E.;Hoshino-Shimuzu, Sumie;
Revista do Instituto de Medicina Tropical de S?o Paulo , 1990, DOI: 10.1590/S0036-46651990000300005
Abstract: in an attempt to find a better t. cruzi antigen and possible immunological markers for the diagnosis of different clinical forms of chagas' disease, amastigote and trypomastigote antigens obtained from immunosuppressed mice infected with t. cruzi (y strain) were assessed in comparison with conventional epimastigote antigens. a total of 506 serum samples from patients with acute and with chronic (indeterminate, cardiac and digestive) forms, from nonchagasic infections, and from healthy individuals were assayed in immunofluorescence (if) tests, to search for igg, igm and iga antibodies. amastigote proved to be the most convenient antigen for our purposes, providing higher relative efficiency indexes of 0.946, 0.871 and 0.914 for igg, igm and iga if tests, respectively. anti-amastigote antibodies presented higher geometric mean titers (gmt) than anti-trypomastigote and anti-epimastigote. anti-amastigote igg antibodies were found in all forms of chagas' disease, and predominantly iga antibodies, in chronic digestive and in acute forms, as well as igm antibodies, in latter forms. thus, tests with amastigote antigen could be helpful for screening chagasic infections in blood banks. practical and economical aspects in obtaining amastigotes as here described speak in favour of its use in developing countries, since those from other sources require more complex system of substruction, specialized personnel or equipment.
Lytic antibodies elicited by Trypanosoma cruzi infection recognize epitopes present on both bloodstream trypomastigote and epimastigote forms of parasite
Takehara, Harumi A.;Cardoso, Diva F.;Silva, Ana M.M. da;Mota, I.;
Revista do Instituto de Medicina Tropical de S?o Paulo , 1988, DOI: 10.1590/S0036-46651988000500004
Abstract: sera of chaga's disease patients containing anti-t. cruzi lytic antibodies were submitted to affinity chromatography using sepharose 4b conjugated with antigen extracted from epimasiigote or trypomasiigote forms of the parasite. epimastigotes were obtained from culture at the exponential growth phase and the trypomastigotes from blood of infected and immunosuppressed mice. antigen of both parasite forms was obtained by sonication of the parasites followed by centrifugation. both antigens were then conjugated to activated sepharose 4b. affinity chromatography was performed by passing sera from chagasic patients through an immunoadsorbent column containing either epimasiigote or trypomasiigote antigens. antibodies bound to the column were eluted with cold 0,2 m glycine buffer ph 2,8. the eluted antibodies were analysed regarding their isotype and lytic activity. the results showed that anti-t. cruzi lytic antibodies present in sera from chagasic patients are mainly located in the igg isotype and recognize epitopes present in both trypomasiigote and epimastigote forms. a brief report of this work has already been published12.
The Oxidative Function of Diferric Transferrin  [PDF]
Frederick L. Crane,Hans L w
Biochemistry Research International , 2012, DOI: 10.1155/2012/592806
Abstract: There is evidence for an unexpected role of diferric transferrin as a terminal oxidase for the transplasma membrane oxidation of cytosolic NADH. In the original studies which showed the reduction of iron in transferrin by the plasma membranes NADH oxidase, the possible role of the reduction on iron uptake was emphasized. The rapid reoxidation of transferrin iron under aerobic conditions precludes a role for surface reduction at neutral pH for release of iron for uptake at the plasma membrane. The stimulation of cytosolic NADH oxidation by diferric transferrin indicates that the transferrin can act as a terminal oxidase for the transplasma membrane NADH oxidase or can bind to a site which activates the oxidase. Since plasma membrane NADH oxidases clearly play a role in cell signaling, the relation of ferric transferrin stimulation of NADH oxidase to cell control should be considered, especially in relation to the growth promotion by transferrin not related to iron uptake. The oxidase can also contribute to control of cytosolic NAD concentration, and thereby can activate sirtuins for control of ageing and growth.
Molecular Structure of Human Transferrin – Transferrin Receptor Complex  [PDF]
Viroj Wiwanitkit
International Journal of Molecular Sciences , 2006, DOI: 10.3390/i7070197
Abstract: Transferrin receptor (TfR) is a glycoprotein mediating the entry of ferrictransferrin (Tf) from the extracellular compartment into the cells. TfR are present on thesurface of many cell types but they are most abundant on cells active in hemoglobinsynthesis. However, the knowledge on the complex, recombination, between Tf and sTfR islimited. Here, the author performs an analysis to study the molecular structure of human Tf- sTfR complex. The output 3D molecular structure from the combination between Tf andTfR is derived. The property as well as geometry of the derived complex was also presented.
Probing molecular interaction between transferrin and anti-transferrin by atomic force microscope
Zhiwen Zheng,Peihui Yang,Gucheng Zeng,Jiye Cai
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-0405-0
Abstract: The interaction between transferrin (Tf) and its antibody was investigated by atomic force microscope. Tf-antibody was immobilized on the Au-coated glass slide, and the specific combination between antibody and antigen was also characterized by AFM. The results showed that holo-transferrin was jogged with anti-transferrin, and binded anti-transferrin more tightly than apo-transferrin. The force-distance curves revealed that the affinity of anti-transferrin and holo-transferrin was much stronger than that of apo-transferrin.
The Oxidative Function of Diferric Transferrin  [PDF]
Frederick L. Crane,Hans L?w
Biochemistry Research International , 2012, DOI: 10.1155/2012/592806
Abstract: There is evidence for an unexpected role of diferric transferrin as a terminal oxidase for the transplasma membrane oxidation of cytosolic NADH. In the original studies which showed the reduction of iron in transferrin by the plasma membranes NADH oxidase, the possible role of the reduction on iron uptake was emphasized. The rapid reoxidation of transferrin iron under aerobic conditions precludes a role for surface reduction at neutral pH for release of iron for uptake at the plasma membrane. The stimulation of cytosolic NADH oxidation by diferric transferrin indicates that the transferrin can act as a terminal oxidase for the transplasma membrane NADH oxidase or can bind to a site which activates the oxidase. Since plasma membrane NADH oxidases clearly play a role in cell signaling, the relation of ferric transferrin stimulation of NADH oxidase to cell control should be considered, especially in relation to the growth promotion by transferrin not related to iron uptake. The oxidase can also contribute to control of cytosolic NAD concentration, and thereby can activate sirtuins for control of ageing and growth. 1. Introduction The remarkable diversity of oxidative activity at the plasma membrane has only recently been brought into focus. Early study of peroxide generation in cells emphasized the role of mitochondria in relation to free radical generation [1, 2]. Other sources of H2O2 such as xanthine oxidase [3], monoamine oxidase [1], or disulfide bond formations [4] have been recognized, but attributed a lesser role. In the plasma membrane the controlled generation of H2O2 by leucocytes to fight infection is well established [5, 6]. More recently, the H2O2 generating capacity in plasma membrane of other types of cells has been recognized and proposed to be the basis for hormone and growth factor response, oxygen sensing [7], and microbicidal action [8–12]. These H2O2 generating systems have all been related to the NADPH oxidase GP91 phox Gp22 phox enzymes first recognized in neutrophils [5, 6]. Seven variations of this NADPH oxidase have been found and are designated as NOX1-5 and Duo NOX1-2 [9, 13]. The reaction with oxygen in all is catalyzed by the oxidation of low-potential cytochrome b 558. The members of the NOX groups are individually expressed in different tissues [9, 12]. Plasma membranes also have NADH oxidase activity [14–16]. Two forms of NADH oxidase have been extracted from plasma membranes and designated cNOX and tNOX [17]. These oxidases do not use cytochrome b558 as a terminal link to oxygen. The isolated enzyme also acts as a
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