The protein pKa values determine the integrand charge difference, T is the temperature, and R is the gas constant. This charge difference between the folded and unfolded protein is calculated for all protein pKa values by PROPKA.
PROPKA relates a protein pKa value to its 3D protein structure. The pKa values of all the ionizable residues in a protein are calculated by determining perturbations, ∆pKa, to a reference water pKa value, pKamodel. Perturbations from desolvation (∆pKaDS), protein dipole interactions (∆pKaQμ), and charge-charge interactions (∆pKaQQ) based on the position and orientation of groups surrounding each ionizable residue are included. Thus, the protein pKa value is expressed as