Identification of an iron–hepcidin complex

Abstract

Short title: Iron-bound hepcidin complexAbbreviations footnote: LEAP: liver expressed antimicrobial peptide; TCEP: Tris-(2-Carboxyethyl)-phosphine; MS: mass spectrometric; TNF-: tumor necrosis factor alpha; MMP: matrix metalloproteinase Following its identification as a liver-expressed antimicrobial peptide, the hepcidin peptide was later shown to be a key player of in iron homeostasis. It is now proposed to be the "iron-hormone" which, by interacting with the iron transporter ferroportin, prevents further iron import into the circulatory system. This conclusion was reached using the corresponding synthetic peptide, emphasizing the functional importance of the mature 25-mer peptide, but omitting the possible functionality of its maturation. From urine-purified native hepcidin, we recently identified a proportion of iron-hepcidin complex. This interaction was further investigated by computer modeling and, based on sequence similarity with metallothionein, a 3D model of hepcidin containing one atom of iron was built. To further characterize these complexes, the interaction with iron was analyzed using different spectroscopic methods. Mono-ferric hepcidin was identified by mass spectrometry, with possibly other complexes containing 2 and 3 atoms of iron respectively, although present in minor amounts. UV/visible absorbance and circular dichroism (CD) studies identified the iron-binding events which were facilitated at physiological pH. Electron paramagnetic resonance (EPR) spectroscopy identified the ferric state of the bound metal, and indicated that the iron-hepcidin complex shares some similarities with the rubredoxin iron-sulfur complex, suggesting the presence of Fe 3+ in a tetrahedral sulfur coordination. The potential roles of iron-binding for hepcidin are discussed where we propose either a regulatory function in the maturation of the pro-hepcidin into the active hepcidin, or as the necessary link in the interaction between hepcidin and ferroportin

Characterisation of hepcidin response to holotransferrin treatment in CHO TRVb-1 cells

“…A putative role of transferrin receptor (TFR)1 in modulating hepcidin expression was suggested [3] but its significance in transferrin-sensing and hepcidin induction has not been sufficiently emphasised. Likewise, even though an involvement of intracellular iron in the maturation of prohepcidin into bioactive hepcidin was postulated [4], its function in hepcidin peptide secretion has not been sufficiently examined. This is partly because of lack of suitable cell lines that could consistently mimic the human hepcidin response to iron treatments.…”

Renal Handling of Circulating and Renal-Synthesized Hepcidin and Its Protective Effects against Hemoglobin–Mediated Kidney Injury

“…4 Because of its important role in iron homeostasis, 5 these observations prompted the hypothesis that hepcidin may have protective effects against iron-mediated AKI. Its mechanisms of action remain elusive, but may include (1) binding of luminal iron, [6][7][8] thus promoting iron excretion, or (2) increased sequestration of renal iron in ferritin in the epithelial cells, thereby reducing serum and luminal iron levels. 1,3,9 Both mechanisms would reduce the formation of iron-induced oxidative stress and subsequent cell damage.…”

Structure and Mode of Action of Microplusin, a Copper II-chelating Antimicrobial Peptide from the Cattle Tick Rhipicephalus (Boophilus) microplus

“…Microplusin Binds to Metals-A growing number of studies have shown that histidine-rich AMPs are able to complex with metal ions such as copper, nickel, zinc, and iron (23,(47)(48)(49)(50). Because microplusin has several histidine residues, 2 at the N terminus, 1 at position 74, and 4 at the C terminus ( Fig.…”

“…We determined the MIC 50 , because microplusin had partial inhibitory activity for some tested microorganisms, even at the highest concentration used (50 M). The recombinant peptide was active against almost all Gram-positive bacteria tested, except for S. aureus (Table 2).…”

“…The microbial growth was assessed by measurements of the A 595 . MIC 100 and MIC 50 were defined as the minimal inhibitory concentration that prevents 100 and 50% of the bacterial growth, respectively. The effect of metals on peptide activity was evaluated by liquid assays using M. luteus incubated with microplusin (50 - (34) or with each component of TES.…”