Table 1. Comparison of the Binding Affinities of TfR Mutants for HFE and Fe-Tf at pH 7.5 and Apo-Tf at pH 6.3.

For each substituted position, residues at that position in human and six other species of TfR—feline, canine, hamster, mouse, rat, and chicken—and two species of TfR2 (human and mouse) are listed in the first column

The second column (HFE Structural Epitope) identifies TfR residues that are part of the crystallographically identified HFE structural epitope. Yes indicates that the residue contains an atom within 4 Å of HFE and No that all atoms of the residue are >4 Å from HFE. The asterisk indicates a glycine residue that is covered by HFE, but which lacks a sidechain and therefore does not contain atoms within 4 Å of HFE (Bennett et al. 2000)

The third column classifies substitutions as to their location or chemical character: HΦ, solvent-exposed hydrophobic residue; H1, H2, or H3, part of the HFE structural epitope on helix 1, 2, or 3 of the TfR helical domain; IDC, part of the TfR interdomain cleft

The fourth column lists the name of the mutant. The § symbol denotes mutants that were also evaluated for HFE and Fe-Tf binding in previous experiments (West et al. 2001). Current results for these mutants agree closely with those reported previously (West et al. 2001). The K_Ds for wild-type TfR are averages derived from 22 independent measurements, and the numbers after the plus/minus sign represent standard deviations. Mutants with significant relative affinity reductions are highlighted (green, between 5-fold and 30-fold; red, greater than 30-fold). Mutants that showed no binding are labeled N.B. ΔΔG values were calculated from the mutant to wild-type affinity ratios and plotted for each mutant in the form of a histogram, shown in Figure S1