Site-specific PPIase with respect to the amino acid N-terminal to the proline residue. Peptides with glutamate, phosphoserine, or phosphothreonine in the -1 position are the best substrates. It is not only able to isomerize small peptides but is also active in protein folding. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0)