PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides (By similarity). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Component of the acid-insoluble organic matrix of calcified layers of the shell (at protein level). Belongs to the cyclophilin-type PPIase family.