Abstact

The antibacterial and antifungal peptide hepcidin (LEAP-1) is expressed in the liver. This circulating peptide has recently been found to also act as a signaling molecule in iron metabolism. As such, it plays an important role in hereditary hemochromatosis, a serious iron overload disease. In this study, we report the solution structures of the hepcidin-20 and -25 amino acid peptides determined by standard two-dimensional (1)H NMR spectroscopy. These small cysteine-rich peptides form a distorted beta-sheet with an unusual vicinal disulfide bridge found at the turn of the hairpin, which is probably of functional significance. Both peptides exhibit an overall amphipathic structure with six of the eight Cys involved in maintaining interstrand connectivity. Hepcidin-25 assumes major and minor conformations centered about the Pro residue near the N-terminal end. Further NMR diffusion studies indicate that hepcidin-20 exists as a monomer in solution, whereas hepcidin-25 readily aggregates, a property that may contribute to the different activities of the two peptides. The nuclear Overhauser enhancement spectroscopy spectra of the hepcidin-25 aggregates indicate an interface for peptide interactions that again involves the first five residues from the N-terminal end.