Table 5. Possible and observed bidentate and complex interactions that are made using amino acid side chains.

The first column lists protein residues that can participate in interactions, classified according to the hydrogen-bonding atoms on the side chains. The second and third columns give the base or base pairs that can potentially participate in bidentate interactions and the examples that are actually observed. - denotes a base pair. The fourth to ninth columns show the possible base combinations for complex interactions in the major and minor grooves, and the interactions that are observed with stacked bases and diagonally-positioned bases. Stacked bases are separated by (.) and diagonally-positioned bases by (\).