Ferroportin is a monomer in vivo in mice

Ferroportin (FPN) is the main iron export protein in mammals. The actual structure of FPN in vivo and the pathogenesis of ferroportin-related disease are unknown. We aimed at studying the structure and biochemical properties of FPN in mouse tissues that are key for iron homeostasis during various iron manipulations in vivo. We performed glycosylation and oligomerization studies in spleen and liver extracts from mice fed a standard, iron-deprived or iron-enriched diet for 5 months. Purification by affinity chromatography and sucrose gradient show that FPN is not part of a large multiprotein complex. Dietary manipulations did not affect the monomeric status of the native or denatured protein. The glycosylation studies showed that ferroportin is digested by peptide: N-glycosidase F but not by endoglycosidase H. The same results were obtained using protein extracts from iron-deficient or iron-loaded mice. In conclusion, our studies indicate that mouse FPN, regardless of the tissue iron status, is glycosylated but not enriched in mannose residues, and that exists mainly in monomeric form. The latter finding may have important implications for understanding the pathogenesis of the disease due to ferroportin mutations.