Correction

S. Lindman, S. Linse, F. A. A. Mulder, and I. André. 2007. pK_a values for side-chain carboxyl groups of a PGB1 variant explain salt and pH-dependent stability. Biophys. J. 92:1:257–66.

A typographical mistake was found in Eqs. 1 and 2 of this article. The correct form of the Henderson-Hasselbalch equation for deprotonation using a Hill parameter to account for nonideality should read:

$${\delta }_{obs}=\frac{\left({\delta }_{HA}+{\delta }_{A^{-}}{10}^{n_h\left(pH-p{K}_a\right)}\right)}{\left(1+{10}^{n_h\left(pH-p{K}_a\right)}\right)},$$ (1)

where δ_obs is the observed chemical shift, and δ_HA and δ_A- are the chemical shifts of the protonated and unprotonated forms, respectively. And for the two-site model:

$${\delta }_{obs}=\frac{\left({\delta }_{1HA}+{\delta }_{1A^{-}}{10}^{\left(pH-p{K}_{a1}\right)}\right)}{\left(1+{10}^{\left(pH-p{K}_{a1}\right)}\right)}+\frac{\left({\delta }_{2HA}+{\delta }_{2A^{-}}{10}^{\left(pH-p{K}_{a2}\right)}\right)}{\left(1+{10}^{\left(pH-p{K}_{a2}\right)}\right)},$$ (2)

where δ₁ corresponds to the chemical shifts of the residue we directly monitor and δ₂ is the contribution of a secondary site on the chemical shift of the monitored site.

Importantly, all data were analyzed with these correct forms of Eqs. 1 and 2, and this correction in no way changes the results or conclusions presented in the original article.

The authors thank Mr. Jelle Slager for bringing this mistake to their attention.