title: Trypanosoma cruzi receptors for human transferrin and their role.
abstract: Trypanosoma cruzi amastigotes present receptors for human transferrin as indicated by the saturable binding of 125I-transferrin to this form of the parasite. Computerized Scatchard analysis revealed one class of receptors present at 8.1 X 10(4) receptors per amastigote with a Kd of 2.82 microM. Immunofluorescence studies indicate that more than 90% of amastigotes bind human transferrin, whereas trypomastigotes do not. Iron is required for amastigote growth in cell-free medium since deferoxamine, an iron chelator, inhibits amastigote growth. Amastigote growth is restored when deferoxamine is removed from the medium. 59Fe-transferrin, which bound to amastigotes at 4 degrees C for 1 h, was readily dissociated from the parasite surface upon treatment with acid. However, this treatment did not disrupt binding that occurred at 37 degrees C for 1 h. Amastigote growth in cell-free medium is inhibited in ferrotransferrin-depleted serum, and addition of ferrotransferrin but not apotransferrin restores parasite growth. Western blots of solubilized amastigote membranes probed with anti-human transferrin receptor antibody recognize a protein of 200 kDa. This protein is present on the amastigote cell surface; therefore, human transferrin seems to interact with a 200-kDa surface amastigote protein receptor. Iron, which is essential for amastigote growth, thus appears to be delivered to T. cruzi amastigotes by transferrin receptor-mediated endocytosis.
authors.affiliation: Division of Biomedical Sciences, School of Graduate Studies, Meharry Medical College, Nashville, TN 37200.
authors.forename: M F
authors.initials: MF
authors.lastname: Lima
authors.forename: F
authors.initials: F
authors.lastname: Villalta
mesh_terms: D000818:Animals; D003429:Cross Reactions; D003676:Deferoxamine / Q000494:pharmacology; D006801:Humans; D007501:Iron / Q000378:metabolism; D007504:Iron Radioisotopes; D011485:Protein Binding; D011990:Receptors, Transferrin / Q000276:immunology / Q000502:physiology*; D014168:Transferrin / Q000378:metabolism*; D014349:Trypanosoma cruzi / Q000378:metabolism*
chemical_list: D007504:Iron Radioisotopes; D011990:Receptors, Transferrin; D014168:Transferrin; D007501:Iron; D003676:Deferoxamine