FK506- and rapamycin-binding proteins (FKBPs) constitute a family of receptors for the two immunosuppressants which inhibit T-cell proliferation by arresting two distinct cytoplasmic signal transmission pathways. PPIases accelerate the folding of proteins (By similarity). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Inhibited preferentially by rapamycin over FK506. Belongs to the FKBP-type PPIase family.