Figure 2.

Grey filled bars indicate the average value ($\langle {\text{ρ}}_i\rangle$) of the charge for each ionizable group i, computed at pH 6.5 by using Eq. (2) for: (a) 10 conformations of 1D3Z, (b) 128 conformations of 1XQQ and (c) 1 X-ray conformation of 1UBQ. Except for 1UBQ, a filled black square and open circle denote the maximum and minimum computed average charge, respectively, from Eq. (1). The N- and C-termini are indicated as N- and C-, respectively. The one-letter code is used for the ionizable groups, followed by a number that represents its position in the sequence of ubiquitin. The values of 3.9, 4.3, 10.5, 10.1, 6.0, and 12.5 were adopted as $p{K}_a^o$ for the ionizable groups of residues Asp, Glu, Lys, Tyr, His, and Arg, respectively, as an average from the data of Perrin.¹⁸ Values of 7.80 and 3.75 for the α-amino and α-carboxyl groups⁴⁰ were used for the $p{K}_a^o$ of the ionizable N- and C-terminal groups, respectively