Copper(II) binding properties of hepcidin

Hepcidin is a peptide hormone that regulates the homeostasis of iron metabolism. The N-terminal domain of hepcidin is conserved amongst a range of species and is capable of binding Cu II and Ni II through the amino terminal copper–nickel binding motif (ATCUN). It has been suggested that the binding of copper to hepcidin may have biological relevance. In this study we have investigated the binding of Cu II with model peptides containing the ATCUN motif, fluorescently labelled hepcidin and hepcidin using MALDI-TOF mass spectrometry. As with albumin, it was found that tetrapeptide models of hepcidin possessed a higher affinity for Cu II than that of native hepcidin. The log K 1 value of hepcidin for Cu II was determined as 7.7. Cu II binds to albumin more tightly than hepcidin (log K 1 = 12) and in view of the serum concentration difference of albumin and hepcidin, the bulk of kinetically labile Cu II present in blood will be bound to albumin. It is estimated that the concentration of Cu II -hepcidin will be less than one femtomolar in normal serum and thus the binding of copper to hepcidin is unlikely to play a role in iron homeostasis. As with albumin, small tri and tetra peptides are poor models for the metal binding properties of hepcidin.