Leishmania spp are intracellular protozoan parasites that cause serious human health problems throughout the world. Infection of mammalian hosts with Leishmania depends on the remarkable ability of these parasites to replicate within macrophage phagolysosomes. A critical adaptation for survival in this harsh environment is an efficient mechanism for gaining access to iron. However, very little is known about how intracellular parasites acquire iron.
We identified LIT1, a novel L. amazonensis membrane protein with extensive similarity to IRT1, a ZIP family ferrous iron transporter from Arabidopsis thaliana. LIT1 was only detectable in amastigotes replicating intracellularly, and when expressed in yeast LIT1 specifically restored iron transport ability. Although L. amazonensis lacking LIT1 (Llit1) grew normally in culture, replication within macrophages was abolished. Consistent with an essential role for LIT1 in intracellular growth as amastigotes, Llit1 parasites were avirulent. Following inoculation into highly susceptible mice, no lesions were detected. Comparing the LIT1 and IRT1 (Arabidopsis iron transporter) sequences revealed conserved residues. We are mutagenizing these residues to determine whether these residues hold functionally important roles in the Leishmania iron transporter LIT1. Furthermore, the intracellular loop between transmembrane III and IV regions of LIT1 is longer than that of IRT1. To decipher the role(s) of this region in LIT1�s function, we deleted distinct segments to identify potential ligand binding domains and/or regulatory domains. The data revealed that none of the segments deleted within these regions affected the ability of the transporter to transport iron in yeast. Interestingly, several of these truncated constructs failed to complement the growth phenotype of the Llit1 Leishmania strain, suggesting the existence of Leishmania regulatory proteins that may regulate LIT1 function. Attempts are being made to identify Leishmania proteins interacting with LIT1, using immuno-precipitation and yeast two hybrid system.