Nevertheless, we observe that compared to normal MD, constant pH MD can increase the sampling of the local conformational space of the protein. In Figure and S17 we show that the HIS4 samples configurations more efficiently in constant PH simulations. Specifically, the hydrogen bond between PHE10 and the HIS4 δ hydrogen is much more stable in normal MD with a fixed protonation of δ-nitrogen (Figure ), whereas in constant pH MD, the HIS4 also samples configurations in which the H-bond is broken (Figure ), in particular around pH=pK a , as evidenced by the distribution of the N-C α -C β -C γ dihedral angle in