Figure 5.

The α₁β₂ interfaces of α₂β⁸²CA⁸²β (yellow) and R2 hemoglobin (magenta) after the superimposition of the α₁β₁ interface as described (1), revealing the presence of two water molecules, Wat1 and Wat2, which are hallmarks of the R2 structure and not found in the R or T quaternary structure. Wat1 is hydrogen bonded to the OD2 of α₁Asp-94 (2.53 Å and 2.48 Å for α₂β⁸²CA⁸²β and R2, respectively) and the amide nitrogen of β₂Asp-99 (2.89 Å and 2.95 Å for α₂β⁸²CA⁸²β and R2, respectively), whereas Wat2 is hydrogen bonded to Wat1 (2.85 Å and 3.19 Å for α₂β⁸²CA⁸²β and R2, respectively).