Abstract
The protozoan parasite Leishmania is the causative agent of serious human infections worldwide. The parasites alternate between insect and vertebrate hosts and cause disease by invading macrophages, where they replicate. Parasites lacking the ferrous iron transporter LIT1 cannot grow intracellularly, indicating that a plasma membrane-associated mechanism for iron uptake is essential for the establishment of infections. Here, we identify and functionally characterize a second member of the Leishmania iron acquisition pathway, the ferric iron reductase LFR1. The LFR1 gene is up-regulated under iron deprivation and accounts for all the detectable ferric reductase activity exposed on the surface of Leishmania amazonensis. LFR1 null mutants grow normally as promastigote insect stages but are defective in differentiation into the vertebrate infective forms, metacyclic promastigotes and amastigotes. LFR1 overexpression partially restores the abnormal morphology of infective stages but markedly reduces parasite viability, precluding its ability to rescue LFR1 null replication in macrophages. However, LFR1 overexpression is not toxic for amastigotes lacking the ferrous iron transporter LIT1 and rescues their growth defect. In addition, the intracellular growth of both LFR1 and LIT1 null parasites is rescued in macrophages loaded with exogenous iron. This indicates that the Fe(3+) reductase LFR1 functions upstream of LIT1 and suggests that LFR1 overexpression results in excessive Fe(2+) production, which impairs parasite viability after intracellular transport by LIT1.
Highlights
Human infections with the protozoan parasite Leishmania spp. represent a serious public health problem
LIT1-deficient parasites are unable to replicate within host macrophages and do not cause skin lesions in mice, indicating that this pathway of iron acquisition is essential for the ability of Leishmania to cause disease [7]
Ferrous iron transporters are expected to work in concert with ferric reductases, which are essential for the generation of the soluble Fe2ϩ substrate for membrane translocation [4]
Summary
Human infections with the protozoan parasite Leishmania spp. represent a serious public health problem. Consistent with the high levels of sequence identity between LFR1 from L. amazonensis and the corresponding genes in L. major (causative agent of cutaneous leishmaniasis in the Old World) (supplemental Fig. S1), live promastigotes from five distinct Leishmania isolates were able to reduce extracellular ferric iron.
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