Figure 1.

(A) Chemical structure of Ace-Pro-NMe, used for quantum chemical calculations. Proline is referred to as the i^th residue and the subscripts for all of the atoms are labeled accordingly. Due to the rigid pyrrolidine ring, the dihedral angle φ is mostly close to −60°, whereas the other dihedral angle ψ is variable. The potential energy profile was created as described in the Materials and Methods. All geometrical parameters were fixed corresponding to the conformation of proline residue, Pro-94, from the protein cytochrome peroxidase (PDB: 4CVI) and the ψ angle was varied. (B) Example of a proline residue from the protein cytochrome peroxidase (PDB: 4CVI) that satisfies the geometrical criteria for the N-H…N H-bond. All of the molecular plots were rendered by Chimera software (40) and the standard colors are used to represent nitrogen, oxygen, carbon, and hydrogen atoms. The same convention is used for all molecular plots. To see this figure in color, go online.