Crystal Structure of the Hemochromatosis Protein HFE and Characterization of Its Interaction with Transferrin Receptor

Division of Biology, California Institute of Technology, Pasadena 91125, USA.
Cell (Impact Factor: 32.24). 05/1998; 93(1):111-23. DOI: 10.1016/S0092-8674(00)81151-4
Source: PubMed


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.

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    • "However, this does not appear to be its primary function since TfR2 knockout mice are capable of iron storage and accumulation [60]. It is thought that the HFE gene product, a MHC class I-type protein, in conjunction with b2-microglobulin associates with either TfR1 or TfR2 and senses transferrin saturation, to consequently regulate hepcidin expression [61] [62] [63]. "
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    • "Common pathogenic HFE-missense mutations are supposed to exert their effect by disrupting the interaction of HFE with B2M and/or TFRC. As an example, C282Y disrupts the disulfide bridge occurring between C225 and C282 sites in the HFE a3-domain, impairing B2M binding and HFE cell surface expression (Lebró n et al, 1998). "
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    ABSTRACT: Hereditary haemochromatosis (HH) is an autosomal recessive disorder characterized by excessive intestinal iron absorption resulting in increased pathological body iron stores. It is typically associated with homozygosity for the c.845G>A (p.C282Y) mutation in the HFE gene. However, other HFE alterations have been reported in affected individuals but their association with the disease is unclear. This study analysed the functional consequences of two HFE mutations, c.829G>A (p.E277K) and c.884T>C (p.V295A). Firstly, it was shown that c.829G>A affects the HFE splicing by diminishing the full length HFE and ivs4_66bp inclusion transcript levels, while increasing the amount of exon 4 skipping transcript. Immunofluorescent techniques showed that the HFE_E277K protein had a diffuse distribution (similar to HFE_C282Y) while HFE_V295A presented at the cell surface and perinuclear compartments (resembling HFE_wt). Immunoprecipitation assays revealed a decreased association of HFE_E277K and HFE_V295A with both β2-microglobulin (B2M; 38 ± 7% and 66 ± 8%, respectively) and transferrin receptor (TFRC, also termed TFR1) (58 ± 2% and 49 ± 16%, respectively). Herein, we prove that both mutations partially abrogate HFE association with B2M and TFRC, crucial for its correct processing and cell surface presentation. Although E277K has a more deleterious effect than V295A, we propose that both mutations may play a role in the development of hereditary haemochromatosis.
    Preview · Article · May 2012 · British Journal of Haematology
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    • "The HFE protein is predominantly expressed in tissues involved in iron storage, such as hepatocytes and macrophages [Holmström et al., 2003; Zhang et al., 2003], and its expression is transcriptionally regulated by hepatic C/EBPα and erythroid GATA-1 [Mura et al. 2004; Makui et al., 2005]. Functional HFE competes with holo-transferrin (holo-Tf) for binding to TfRC (OMIM 190010), and it interacts with TfR2 (OMIM 604720) independently of holo-Tf [Parkkila et al., 1997; Feder et al., 1998; Lebron et al., 1998; Gross et al., 1998; Chen et al., 2007]. Patients affected with HFE-linked hemochromatosis, TfR2-linked hemochromatosis, and Hfe -/-mice, have inappropriately-low expression of the hepcidin peptide which regulates the ferroportin transmembrane iron exporter by inducing its internalization and degradation; both HFE and TfR2 are involved in a HAMP (OMIM 606464) regulatory pathway [Pigeon et al., 2001; Nicolas et al., 2002; Nemeth et al., 2004; Bridle et al., 2003; Nemeth et al., 2005; Wallace et al., 2009]. "
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    ABSTRACT: Hereditary hemochromatosis is a common-recessive-autosomal disease characterized by progressive iron overload, and its prevalence correlates with c.845G>A (p. C282Y) mutation of the HFE gene. Two other variants c.187C>G and c.193A>T are associated with a mild iron overload phenotype. The correlation studies have revealed incompletely penetrance of the HFE mutations, as well as the lack of mutation on some chromosomes from patients. We screened for SNPs before examining allele and haplotype association with elevated iron parameters. We confirmed that the c.845G>A mutation is in complete linkage disequilibrium with a unique haplotype, whereas two haplotypes proved to account for 79.8 and 20.2% of the c.187G chromosomes whose only difference was the g.4694C>G variation. A greater prevalence of the g.4694G allele among patients' chromosomes, compared to controls, was observed. In addition, among non-mutant chromosomes the analyses revealed a risk haplotype and a protective haplotype, and the g.4694G and the c.1007-47A alleles were associated with a higher risk of elevated iron parameters. We determined that the g.4694C allele was located within a putative hypoxia-response element, protein binding was evidenced and was reduced with the g.4694C>G change. In addition, IVS4 was not spliced as well in the c.1007-47A allele compared to the c.1007-47G allele.
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