Distribution of Tfrc mutations identified in ENU mutagenesis screens. (A) Amino acid sequence of the mouse (upper) and human (lower) ectopic helical domain of the Tfrc gene. Mutations identified in murine ENU mutagenesis screens are highlighted (red), with their corresponding RBC mutant strain. Known ligand binding positions include Tf binding (yellow), HFE binding (blue), and sites with overlapping Tf/HFE binding (gray). (B) Three-dimensional structure of the murine TfR-Tf complex (PD entry 3S9L) inspected by PyMOL (version 2.0.3). A cluster of Tfrc mutations (RBC5, orange; RBC6, blue; RBC21, red) is highlighted. (C) Closer inspection of the RBC21 mutation and its positioning within the TfR-Tf complex. The R654 amino acid (human equivalent, R651) is shown to have a direct Tf binding role via interactions with Tf amino acids C368 and D356. Other mutation sites (RBC5, RBC6) are suggested to play structural roles within the receptor.