Fig. 8. Representative proteins showing the three different types of ambifunctional HBs in Ser–Asn (top) and Tyr–Gln (bottom) residue pairs in our data set: shorter d(N⋯O) (left), equivalent length d(N⋯O) and d(O⋯O) (middle), and shorter d(O⋯O) (right). The Ser–Asn pairs correspond to PDB IDs (left to right): 1SFS, 2VOV, and 1O4Y, and the Tyr–Gln pairs to PDB IDs (left to right): 3EPW, 3BVU, and 4B9F. Specific HBs are indicated by black dashed lines between the heavy atoms in residue pairs with annotated distances (black, in Å) and N/O–H⋯O angles (light green, in °). Hydrogen atoms added for all proteins and relaxed with constrained heavy atoms are shown as translucent spheres. The orange and green dashed lines indicate additional stabilizing interactions observed with respect to the residue pair with nearby residues and solvent molecules, respectively. All residues are labeled by one-letter amino acid codes and residue numbers.