Characterisation of the transition metal binding properties of hepcidin
Résumé
Synopsis; Accumulating evidence suggests that hepcidin, a 25 residue peptide hormone, is the master regulator of iron metabolism. Further evidence suggests that the five N-terminal amino acids are crucial for mediating its biological function. With a histidine residue at position 3, this region also has the potential to bind divalent metal ions. To characterise this hepcidin-metal interaction in detail this study utilises electrospray mass spectrometry to measure the binding of a range of metal ions to wild type and mutant human and murine hepcidins. In addition the biological effects of these point mutations were tested on Caco-2 and HEK 293T human cell lines and in mice. Our results show that hepcidin-25 can form complexes with copper, nickel and zinc, though we failed to detect any hepcidin-25 binding to either ferric or ferrous ions. The greatest affinity observed was between hepcidin-25 and copper with a dissociation constant << 1 µM. Substituting the histidine at position 3 in human hepcidin-25 and comparably the asparagine at position 3 in murine hepcidin-25 with alanine markedly diminished the affinity for copper. The amino acid substitutions also decreased the biological activity of hepcidin-25; namely repression of ferroportin protein levels and hypoferraemia. In summary the high affinity of hepcidin for copper suggests that hepcidin could bind copper in vivo and this may be of biological relevance.
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