Figure 6.

Schematic of one half of the symmetrical α1β2 interface, showing only the C^α atoms of four residues to represent the switch and joint contacts, in the IsdH^N2N3–metHb complex (PDB entry 4xs0; yellow), O₂-ligated R-­state Hb (PDB entry 2dn1; red) and deoxy T-state Hb (PDB entry 2dn2; blue), prepared by superposition of the α1β1 dimers in the BGH frame (Baldwin & Chothia, 1979 ▸). Dashed lines indicate approximately equal interatomic distances in the three structures (Table 6 ▸). Arrowheads indicate displacement of R-state atoms (red) or IsdH^N2N3–metHb complex atoms (yellow) relative to the T-state structure (blue).