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Typical configurations of the His37 tetrad and its surrounding solvation structure corresponding to the free energy minimum in the (A) +0 PMF, (B) +1 PMF, (C) +2 PMF, and (D) +2 PMF with amphipathic helices. The hydrogen bonds between water molecules as well as those between water molecules and His37 tetrad are depicted as dotted lines. No direct hydrogen bonds between histidine residues are observed in any of the structures.
