PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides. Acts on the folding of rhodopsin RH1 and RH2 (but not RH3) and is required for visual transduction. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Expressed specifically in photoreceptor cells. Belongs to the cyclophilin-type PPIase family.