Estimative of the protonation state.

The protonation state of the loops and active site residues were calculated through the values of the pKa provided by PROPKA 3.0. The evaluation was performed using the representative conformation for each scenario on its pH. The relation [A-]/[HA] was obtained employing the Henderson-Hasselbalch equation (log([A-]/[HA]) = pH-pKa). Values lower and higher than 1 means a residue protonated (italic) and deprotonated (bold), respectively. The analysis indicates a positive variation of charge in H90, E92 and E100 with the increase of the acidity, explaining the extension of the loop 1. Also, as consequence of the conformational change and pH variation, the residues E198, E235 and H283 show differences to pH 4 and pH 6 when compared to pH 8. The charge variation of these constituents of the active site illustrates the role of balance between the extension of the loop 1 and the protonation state of key residues of the active site.Estimative of the protonation state.