PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Binds to the immunosuppressant drug FK506. Belongs to the FKBP-type PPIase family. FKBP1 subfamily.