A trypanosomatid protein specifically interacts with a mammalian iron-responsive element

Intracellular iron homeostasis of vertebrates and invertebrates is mediated through the interaction of iron-regulatory proteins (IRPs) with mRNAs containing a bulged hairpin-loop structure termed the iron-responsive element (IRE). We detected a protein within extracts prepared from Leishmania tarentolae that specifically interacts with a mammalian IRE; mutations to the IRE that inhibit the interaction with the mammalian protein have a corresponding effect on the interaction with the L. tarentolae protein. The disassociation constant noted for the interaction of the mammalian IRE with the L. tarentolae protein was 0.7 +/- 0.3 mu M, whereas that recorded for the interaction with the mammalian IRP under these conditions was 5 +/- 2 nM. The interacting L. tarentolae protein potentially places the RNA-binding site of the IRP near the root of the eukaryotic evolutionary tree. However, unlike that of the mammalian IRPs, the L. tarentolae IRE-binding activity was not induced by growth in iron-depleted media.