FK506 binding proteins (FKBPs) are a family of highly conserved proteins in eukaryotes.
The prototype of this protein family, FKBP12, is the binding partner for immunosuppressive drugs
FK506 and rapamycin. FKBP12 functions as a cis/trans peptidyl prolyl isomerase (PPIase) that catalyzes
interconversion between prolyl cis/trans conformations. Members of the FKBP family contain
one or several PPIase domains, which do not always exhibit PPIase activity yet are all essential for
their function. FKBPs are involved in diverse cellular functions including protein folding, cellular signaling,
apoptosis and transcription. They elicit their function through direct binding and altering conformation of their target
proteins, hence acting as molecular switches. In this review, we provide a general summary for the structures and diverse
functions of FKBPs found in mammalian cells.