Figure 4.

Enzyme-substrate intermolecular hydrogen bonds between CypA and the substrate in the (A) trans, (B) transition-state, and (C) cis configurations. Hydrogen bonds are measured from heavy atom to heavy atom. (Magenta curve) Contact between the Arg⁵⁵ guanidinium carbon and the carbonyl oxygen of the substrate Pro. (Royal-blue curve) Contact between the backbone nitrogen of Asn¹⁰² and the carbonyl oxygen of Ala of the -Ala-Pro- motif. (Cyan curve) Contact between the backbone oxygen of Asn¹⁰² and nitrogen of Ala of the -Ala-Pro- motif. (Orange curve) Contact between the side-chain amino nitrogen of Gln⁶³ and the carbonyl oxygen of Ala, preceding the -Ala-Pro- motif.