A motif of four consecutive peptide residues, of which the i+2 residue is proline, and that may contain one H-bond, which, if present, is between the main-chain CO of the first residue and the main-chain NH of the fourth and is characterized by the dihedral angles: Residue(i+1): phi ~ -60 degrees, psi ~ 120 degrees. Residue(i+2): phi ~ -90 degrees, psi ~ 0 degrees.