The N-terminus of hepcidin is essential for its interaction with ferroportin: structure-function study

Abstract

Hepcidin is the principal iron-regulatory hormone. It acts by binding to the iron exporter ferroportin, inducing its internalization and degradation, thereby blocking cellular iron efflux. The bioactive 25 amino acid (aa) peptide has a hairpin structure stabilized by 4 disulfide bonds. We synthesized a series of hepcidin derivatives and determined their bioactivity in a cell line expressing ferroportin-GFP fusion protein, by measuring the degradation of ferroportin-GFP and the accumulation of ferritin after peptide treatment. Bioactivity was also assayed in mice by the induction of hypoferremia. Serial deletion of N-terminal amino acids caused progressive decrease in activity which was completely lost when 5 N-terminal aa's were deleted. Synthetic 3-aa and 6-aa N-terminal peptides alone, however, did not internalize ferroportin and did not interfere with ferroportin internalization by native hepcidin. Deletion of 2 C-terminal aa's did not affect peptide activity. Removal of individual disulfide bonds by pairwise substitution of cysteines with alanines also did not affect peptide activity in vitro. However, these peptides were less active in vivo, likely because of their decreased stability in circulation. G71D and K83R, substitutions previously described in humans, did not affect hepcidin activity. Apart from the essential nature of the N-terminus, hepcidin structure appears permissive for mutations. (Blood. 2006;107:328-333)

Hepcidin Bound to α2-Macroglobulin Reduces Ferroportin-1 Expression and Enhances Its Activity at Reducing Serum Iron Levels

“…Similar results have been observed for ␣ 2 M-MA binding to defensin, HNP1, which is a cysteine-rich, anti-microbial peptide with structural similarities to hepcidin (17,56). Notably, in both hepcidin and HNP1, all cysteine residues are engaged in intra-molecular disulfide bonds (17,57). The mechanism of HNP1⅐␣ 2 M-MA binding suggested by Panyutich and Ganz (17) may involve thiol-disulfide interchange between ␣ 2 M-MA and HNP1.…”

Effect of bariatric surgery on weight loss, inflammation, iron metabolism, and lipid profile

“…Recently, a complex regulatory network that governs iron traffic emerged and pointed to hepcidin as a major evolutionary conserved regulator of iron distribution (23,24). This small hormone produced by the mammalian liver has been proposed as a central mediator of dietary iron absorption.…”

The role of lysosomes in iron metabolism and recycling

“…This feedback mechanism is important for the regulation of circulating iron by preventing iron export (Knutson et al, 2005, Nemeth et al, 2006. Exactly how hepatocyte iron regulates the production of hepcidin is presently not known.…”