We then inspected the composition of the soaking solution which was used for the crystal structure determination: the details are given in Table . This solution contains a significant amount of organic solvents, namely methanol, DMSO and MPD, totalling more than 50% (v/v). We hypothesized that due to organic solvents, the pH value of the entire solvent system is lowered (compared to physiological conditions). Therefore, this soaking solution was reconstituted and its pH was measured. As expected, the pH value decreases 1.6 units, from 6.9 to 5.3.