The immunophilins are a highly conserved family of cis-trans peptidyl-prolyl isomerases that bind to and mediate the effects of immunosuppressive drugs, such as cyclosporin, FK506 and rapamycin. Immunophilins have also been implicated in protein folding and trafficking within the endoplasmic reticulum (ER). FKBP11 (FK506-binding protein 11), also known as FKBP19 or peptidyl-prolyl cis-trans isomerase FKBP11, is a 201 amino acid single-pass membrane protein belonging to the FKBP-type PPIase family, a group of proteins known to catalyze the folding of proline-containing polypeptides. Containing one PPIase FKBP-type domain, FKBP11 is expressed in secretory tissues such as pancreas, pituitary, stomach, lymph node and salivary gland, and is encoded by a gene that maps to human chromosome 12q13.12. FK506 and rapamycin are known to inhibit FKBP11’s peptidyl-prolyl isomerase activity.