A structural model of human
ferroportin has been built using two
Escherichia coli proteins belonging to the major facilitator superfamily of transporters. A potential
iron binding site was identified in the inward-open conformation of the model, and its relevance was tested through measurement of
iron export of HEK293T cells expressing wild-type or mutated
ferroportin. Aspartates 39 and 181 were found to be essential for the transport ability of the
protein. Noteworthy, the D181V mutation is naturally found in
type 4 hemochromatosis with reticuloendothelial system
iron retention phenotype. The outward-open conformation of
ferroportin was also predicted, and showed that significant conformational changes must occur in the inward- to outward-open transition of
ferroportin. In particular, putative
iron ligands move several ångströms away from each other, leading to the logical conclusion that the
iron binding site is not occupied by the
metal in the outward-open conformation of
ferroportin.