Iron regulatory and bactericidal properties of human recombinant hepcidin expressed in Pichia pastoris

Hepcidin is a circulating cysteine-rich peptide with antimicrobial properties. It functions as a hormonal regulator of iron homeostasis by controlling iron efflux from target cells via ferroportin (FPN1), which is internalized and degraded upon hepcidin binding. Because of its profound biomedical significance, hepcidin has become the target of intense biochemical studies. The aim of this study was to produce functional recombinant hepcidin in sufficient quantities for advanced research or potential clinical use, as the native hepcidin can be isolated from urine in very low yield. We report the expression, purification and functional characterization of hepcidin variants in yeast P. pastoris. The yield of untagged hepcidin 20- and 25-mer peptides was too low for complete functional characterization. By contrast, Hep20 and Hep25 tagged with either single 6xHis or double Myc-6xHis epitopes were expressed at high quantities (5-7mg/l of culture), yet mostly in oligomeric forms. Purification of monomeric tagged hepcidins was achieved by size exclusion chromatography, with a yield of 0.5-1mg/l of culture. All recombinant hepcidins exhibited bacteriostatic activity and the ability to control cellular iron homeostasis, with Hep25-His being the most potent. Thus, Hep25-His promoted an increase in the levels of the labile iron pool (LIP) in macrophages and consistently bound to ferroportin (FPN1) causing its internalization and the subsequent downregulation of transferrin receptor 1 (TfR1) expression. Analysis by mass-spectrometry suggested that all eight cysteines participated in disulfide bond formation. Our results suggest that only the recombinant Hep25-His monomer was a fully active peptide. As Hep25-His faithfully recapitulates the functional properties of native Hep25, it represents a powerful tool for biochemical studies and potential diagnostic and therapeutic applications.