Crystal Structure of the Hemochromatosis Protein HFE and Characterization of Its Interaction with Transferrin Receptor
ABSTRACT HFE is an MHC-related protein that is mutated in the iron-overload disease hereditary hemochromatosis. HFE binds to transferrin receptor (TfR) and reduces its affinity for iron-loaded transferrin, implicating HFE in iron metabolism. The 2.6 A crystal structure of HFE reveals the locations of hemochromatosis mutations and a patch of histidines that could be involved in pH-dependent interactions. We also demonstrate that soluble TfR and HFE bind tightly at the basic pH of the cell surface, but not at the acidic pH of intracellular vesicles. TfR:HFE stoichiometry (2:1) differs from TfR:transferrin stoichiometry (2:2), implying a different mode of binding for HFE and transferrin to TfR, consistent with our demonstration that HFE, transferrin, and TfR form a ternary complex.
SourceAvailable from: Alexandre Reuben[Show abstract] [Hide abstract]
ABSTRACT: MHC class I antigen presentation is an ubiquitous process by which cells present endogenous proteins to CD8+ T lymphocytes during immune surveillance and response. Accordingly, classical MHC I molecules are up-regulated in response to inflammatory stimuli to favor immune recognition and pathogen clearance. HFE is a non-classical, MHC Ib molecule which acts as a negative regulator of iron absorption. HFE has been linked to the development of hereditary hemochromatosis (HH), an iron overload disease often associated to immune defects. Firstly, we studied the impact of HFE expression on MHC I antigen presentation, as a hypothesis for HH-associated immunological defects observed in HFEC282Y-mutated HH patients. Secondly, we evaluated whether, like its classical MHC I counterparts, HFE expression could be modulated in response to peripheral blood mononuclear cell (PBMC) inflammation. We developed an antigen presentation system in which we control MHC I expression, HFE expression, and expression of a model antigen for which we have generated antigen-specific CD8+ T lymphocytes. Our results demonstrate that wild-type HFE (HFEWT), but not C282Y- mutated HFE (HFEC282Y), inhibits recognition of MHC I antigens. We further demonstrate that inhibition of antigen recognition is maintained regardless of MHC I surface levels, β2- microglobulin competition, HFE ability to interact with transferrin receptor, antigen origin, or epitope affinity. We identified the α1-2 domains of HFEWT as being responsible for inhibiting antigen recognition. However, recognition of externally peptide-pulsed 293-A2 remained uninhibited in presence of HFEWT, indicating that HFE may affect T cell recognition by interfering with intracellular antigen processing. We also questioned whether activated T lymphocytes may influence HFE expression. We established that HFE is widely expressed in healthy human tissues and induced in colon cancer, breast cancer, lung cancer, kidney cancer and melanoma cell lines. Furthermore, HFE mRNA expression was drastically inhibited in all tumor cell lines when exposed to activated T lymphocytes. Down-regulation of HFE mRNA expression was independent of cell contact and appears to be partially mediated by GM-CSF, IFN-γ, and TNF. Overall, these data suggest that host T lymphocytes may alter HFE expression levels in the inflammatory microenvironment, which could, in turn, promote recognition of MHC I antigens presented to antigen-specific CD8+ T lymphocytes. Accordingly, this could suggest a new physiological role for HFEWT in the MHC I antigen presentation pathway, which could modulate antigen immunogenicity and the cellular immune response.12/2013, Degree: Ph.D., Supervisor: Manuela M. Santos, Réjean Lapointe
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ABSTRACT: Hepcidin, a 25 aa cysteine rich peptide acts as a regulator of body iron metabolism. It contains 8 cysteines involved in 4 disulfide bridges. Hepcidin is supposed to bind iron, and we propose as metal binding site a N2S2 cavity, CysS-SCys-X-CysS-SCys. Oxidative demetallation should restore the disulfide bridges. This hypothesis has been assayed using pseudopeptidic bis-disulfides ligands. They were metalated under reductive conditions to give FeIII and CuIII complexes, the later have been characterized by X-ray crystallography. All complexes revert back with iodine to the disulfide species along with metal release. Peptide analogs of hepcidin were hand-made or synthesized on a synthesizer by solid phase peptide synthesis. Analogs with 1, 2 and 3 bridges were obtained by random or regioselective oxidation. The 1 and 2 bridges peptides were active and induce as hepcidin the degradation of ferroportin.12/2009, Degree: PhD, Supervisor: Alain Tomas et Isabelle Artaud
Journal of the American Society of Nephrology 02/2003; 14(2):327-337. DOI:10.1097/01.ASN.0000046961.04917.83 · 9.47 Impact Factor