Production and characterization of functional recombinant hybrid heteropolymers of camel hepcidin and human ferritin H and L chains

Structural and functional characterisation of HepTH1-5 peptide as a potential hepcidin replacement

Hepcidin is a principal regulator of iron homeostasis and its dysregulation has been recognised as a causative factor in cancers and iron disorders. The strategy of manipulating the presence of hepcidin peptide has been used for cancer treatment. However, this has demonstrated poor efficiency and has been short-lived in patients. Many studies reported using minihepcidin therapy as an alternative way to treat hepcidin dysregulation, but this was only applied to non-cancer patients. Highly conserved fish hepcidin protein, HepTH1-5, was investigated to determine its potential use in developing a hepcidin replacement for human hepcidin (Hepc25) and as a therapeutic agent by targeting the tumour suppressor protein, p53, through structure-function analysis. The authors found that HepTH1-5 is stably bound to ferroportin, compared to Hepc25, by triggering the ferroportin internalisation via Lys42 and Lys270 ubiquitination, in a similar manner to the Hepc25 activity. Moreover, the residues Ile24 and Gly24, along with copper and zinc ligands, interacted with similar residues, Lys24 and Asp1 of Hepc25, respectively, showing that those molecules are crucial to the hepcidin replacement strategy. HepTH1-5 interacts with p53 and activates its function through phosphorylation. This finding shows that HepTH1-5 might be involved in the apoptosis signalling pathway upon a DNA damage response. This study will be very helpful for understanding the mechanism of the hepcidin replacement and providing insights into the HepTH1-5 peptide as a new target for hepcidin and cancer therapeutics.Communicated by Ramaswamy H. Sarma.

Production of Recombinant Human Hybrid Ferritin with Heavy Chain and Light Chain in Escherichia coli and its Characterization

BACKGROUND

Natural human ferritin generally contains 24 subunits with different ratios of heavy chain to light chain, and the ratio of both subunits varies depending on tissue distribution and pathological conditions. However, the production of recombinant hybrid ferritin with both subunits is more challenging.

OBJECTIVE

This study aimed to prepare the recombinant hybrid ferritin for prokaryotic expression and characterize its structure and physicochemical properties.

METHODS

A prokaryotic expression vector of pACYCDuet-1 harboring the two individual genes of human ferritin heavy chain and light chain (FTH/FTL-pACYCDuet-1) was constructed and transfected into Escherichia coli bacteria. Then the genes were co-induced by IPTG to express.

RESULTS

The ferritin was purified by hydrophobic interaction chromatography combining size exclusion chromatography and verified by mass spectrometry and characterized by spectral and morphological analysis.

CONCLUSION

FTH and FTL subunits were successfully co-assembled into a hybrid ferritin nanoparticle (rhFTH/L). The structure of rhFTH/L was demonstrated highly ordered and fairly compact. Besides, the hybrid rhFTH/L nanoparticle was shown more sensitive to thermal stress and reduced stability when compared with that of both individual rhFTH and rhFTL.

Biochemical, Biophysical and Functional Characterization of an Insoluble Iron Containing Hepcidin–Ferritin Chimeric Monomer Assembled Together with Human Ferritin H/L Chains at Different Molar Ratios

Hepcidin and ferritin are key proteins of iron homeostasis in mammals. In this study, we characterize a chimera by fusing camel hepcidin to a human ferritin H-chain to verify if it retained the properties of the two proteins. The construct (HepcH) is expressed in E. coli in an insoluble and iron-containing form. To characterize it, the product was incubated with ascorbic acid and TCEP to reduce and solubilize the iron, which was quantified with ferrozine. HepcH bound approximately five times more iron than the wild type human ferritin, due to the presence of the hepcidin moiety. To obtain a soluble and stable product, the chimera was denatured and renatured together with different amounts of L-ferritin of the H-chain in order to produce 24-shell heteropolymers with different subunit proportions. They were analyzed by denaturing and non-denaturing PAGE and by mass spectroscopy. At the 1:5 ratio of HepcH to H- or L-ferritin, a stable and soluble molecule was obtained. Its biological activity was verified by its ability to both bind specifically cell lines that express ferroportin and to promote ferroportin degradation. This chimeric molecule showed the ability to bind both mouse J774 macrophage cells, as well as human HepG2 cells, via the hepcidin–ferroportin axis. We conclude that the chimera retains the properties of both hepcidin and ferritin and might be exploited for drug delivery.

Production and characterization of a fusion form of hepatitis E virus tORF2 capsid protein in Escherichia coli

Hepatitis E virus (HEV) is a nonenveloped virus causing an emerging zoonotic disease posing a severe threat to the public health in the world, especially to pregnant women. In this study, a truncated form (aa 368-606) of the open reading frame 2 of the capsid protein (tORF2-HEV), a major structural protein of HEV, was expressed in Escherichia coli. This work characterizes for the first time, the fused Glutathione-S-Transferase-tagged tORF2 (GST-tORF2) and tORF2-HEV forms in E. coli. The fusion protein was purified by affinity chromatography with a purity higher than 90% and to yield about 27% after thrombin digestion. The purified GST-tORF2 protein was then characterized by western blot, using anti-GST antibodies, and CD spectroscopy. The GST-tORF2 and tORF2-HEV proteins were shown to be efficient to develop an ELISA test to detect anti-HEV IgG in mice sera immunized with a recombinant full length ORF2 protein. Sera showed a significant increase of the absorbance signal at 450 nm, in plate wells coated with a quantity of 0.5, 1 and 2 µg of proteins. ELISA plates coated with the purified GST-tORF2 and tORF2-HEV showed similar response when compared to the HEV ELISA where total insect cell lysate, infected with the recombinant baculovirus expressing full ORF2, was used as positive control.

Cellular binding analysis of recombinant hybrid heteropolymer of camel hepcidin and human ferritin H chain. The unexpected human H-ferritin binding to J774 murine macrophage cells

Ferritin is a molecule with enormous potentiality in biotechnology that have been already used to encapsulate molecules, as contrast in magnetic resonance imaging and to carry epitopes. We proposed to use it to carry another key protein of iron metabolism, hepcidin that is a small hormone peptide that control systemic iron homeostasis. In this work, we purified the previously produced camel hepcidin and human H-ferritin heteropolymer (HepcH-FTH) and to monitor its binding capability toward J744 cell line in presence or absence of ferric ammonium citrate. Fused camel hepcidin and human H-ferritin monomer (HepcH) as well as the assembled HepcH-FTH heteropolymer (ratio 1:5) was easily purified by a one-step purification using size exclusion chromatography. SDS-PAGE electrophoresis of HepcH, purified from soluble and insoluble fractions, showed a single band of 24 kDa with an estimated purity of at least 90%. The purification yields of HepcH from the soluble and insoluble fractions was, respectively, of about 6.80 and 2 mg/L of bacterial culture. Time curse cellular binding assays of HepcH-FTH revealed its great potential to bind the J774 cells after 15 min of incubation. Furthermore, HepcH-FTH was able to degrade ferroportin, the unique hepcidin receptor, even after 30 min of incubation with J774 cells treated with 100 µM ferric ammonium citrate. In conclusion, we proposed ferritin as a peptide carrier to promote the association of the hybrid HepcH-FTH nanoparticle with a particular type of cell for therapeutic or diagnostic.

Molecular cloning, expression and characterization of secreted ferritin in the silkworm, Bombyx mori

Ferritin is a ubiquitous iron storage protein which plays key role in regulating iron homeostasis and metabolism. In this paper, the ferritin heavy chain homologs (HCH) and light chain homologs (LCH) from Bombyx mori (BmFerHCH and BmFerLCH) were amplified through PCR and cloned into the expression vector pET-30a(+). The recombinant BmFerHCH and BmFerLCH expressed in Escherichia coli were in the form of insoluble inclusion bodies, indicating that the two proteins were not in their natural structural conformation. In order to obtain refolded ferritin in vitro, the inclusion bodies (BmFerHCH and/or BmFerLCH) were dissolved in denaturing buffer (100 mM Tris, 50 mM Glycine, 8 M urea, 5 mM DTT, pH 8.0) and then refolded in refolding buffer (100 mM Tris, 400 mM L-arginine, 0.2 mM PMSF, 0.5 mM DTT). The result showed that it was only when both BmFerHCH and BmFerLCH were present together in the denaturing buffer that refolding was successful and resulted in the formation of heteropolymers (H-L chain dimers) over homopolymers (H-H chain or L-L chain dimers). Moreover, the molecules (NaCl, Triton and glycerol) were found to enhance protein refolding. The optimum temperature, pH and ratios of BmFerHCH/BmFerLCH required for refolding were found to be 10 °C, pH 7, 1:1 or 1:2, respectively. Finally, the refolded ferritin had the ability to store iron, exhibited ferroxidase activity, and could withstand high temperatures and pH treatment, which is consistent with ferritin in other species.