Figure 2.

Hydrogen bond formations of water molecules with amino acids’ side chains at neutral pH. Aspartic acid (D) and glutamic acid (E) (four water molecules), asparagine (N) and glutamine (Q) (four water molecules), serine (S), threonine (T), and tyrosine (Y) (three water molecules), arginine (R) (five water molecules), lysine (K) (three water molecules), histidine (H) (two water molecules), and tryptophan (W) (one water molecule).