Figure 6

Effect of H2B H106, H46 and H2A D89 protonation on acidic patch electronegativity. Calculated electrostatic surface potentials reflecting different protonation states of residues in the acidic patch. In (a) all titratable residues are assigned to their dominant protonation state at pH 7.4, according to measured pKa values in Table 1. In (b), H2B H106 is protonated (positive charge), which is protonated for 12% at pH 7.4. In (c), H2B H106 and H46 (positive) and H2A D89 (neutral) are protonated, reflecting the least electronegative state at slightly acidic pH (pH 6). Location of key acidic patch residues indicated together with their net charge, yellow = H2A; red = H2B.