Identification and isolation of the Leishmania transferrin receptor

In a previous report, we have presented several lines of evidence, derived from widely different methodologies, suggesting that Leishmania has specific receptors for transferrin with a Kd similar to the mammalian transferrin receptor. This paper describes the identification, purification, and biochemical characterization of Leishmania transferrin receptor. The Leishmania transferrin receptor, detected on intact parasites by immunoperoxidase staining, was first identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Western blot analysis, using 125I-transferrin, as a 70-kDa protein. It has been isolated initially from Leishmania infantum promastigotes using affinity chromatography on a transferrin-Sepharose column and, subsequently, from Leishmania major promastigotes. The use of polyclonal antisera to the purified 70-kDa Leishmania transferrin receptor and to the purified rat transferrin receptor showed that the two receptors are antigenically distinct. The 70-kDa Leishmania transferrin receptor was subsequently characterized as an integral membrane glycoprotein. The monomeric state of the Leishmania transferrin receptor was demonstrated by gel filtration of purified receptor complexed with 125I-transferrin. Thus, the Leishmania transferrin receptor, unlike the mammalian receptor, is not a disulfide-linked dimer but a single 70-kDa polypeptide.