Comparison of the Interactions of Transferrin Receptor and Transferrin Receptor 2 with Transferrin and the Hereditary Hemochromatosis Protein HFE

The transferrin receptor (TfR) interacts with two proteins important for iron metabolism, transferrin (Tf) and HFE, the protein mutated in hereditary hemochromatosis. A second receptor for Tf, TfR2, was recently identified and found to be functional for iron uptake in transfected cells (Kawabata, H., Germain, R. S., Vuong, P. T., Nakamaki, T., Said, J. W., and Koeffler, H. P. (2000) J. Biol. Chem. 275, 16618-16625). TfR2 has a pattern of expression and regulation that is distinct from TfR, and mutations in TfR2 have been recognized as the cause of a non-HFE linked form of hemochromatosis (Camaschella, C., Roetto, A., Cali, A., De Gobbi, M., Garozzo, G., Carella, M., Majorano, N., Totaro, A., and Gasparini, P. (2000) Nat. Genet. 25, 14-15). To investigate the relationship between TfR, TfR2, Tf, and HFE, we performed a series of binding experiments using soluble forms of these proteins. We find no detectable binding between TfR2 and HFE by co-immunoprecipitation or using a surface plasmon resonance-based assay. The affinity of TfR2 for iron-loaded Tf was determined to be 27 nM, 25-fold lower than the affinity of TfR for Tf. These results imply that HFE regulates Tf-mediated iron uptake only from the classical TfR and that TfR2 does not compete for HFE binding in cells expressing both forms of TfR. ; © 2000 by The American Society for Biochemistry and Molecular Biology, Inc. Received for publication, September 22, 2000 Published, JBC Papers in Press, October 10, 2000, DOI 10.1074/jbc.C000664200 [Accelerated Publication] We thank Dr. Peter Snow of the Caltech Protein Expression Facility for construction of recombinant baculovirus expressing TfR2 and Dr. Andrew Herr for help with biosensor analyses. This work was supported by the Howard Hughes Medical Institute (to P. J. B. and N. C. A.), Grant DRG-1445 from the Cancer Research Fund of the Damon Runyon-Walter Winchell Foundation Fellowship (to A. P. W.), and National Institutes of Health Grant DK 54488 (to C. A. E.).The costs of publication of this article were ...