FK506-binding protein family (FKBP) (FKBP)

The FK506-binding protein (FKBP) family consists of a group of immunophilins characterized by their peptidyl-prolyl cis-trans isomerase (PPIase) activity, which facilitates the folding of proteins containing proline residues [NIH, Wikipedia]. These proteins function as molecular chaperones and are involved in a wide array of cellular processes, including signal transduction, steroid receptor trafficking, and the regulation of calcium release channels [NIH, PubMed]. The most prominent member, FKBP12, is the primary intracellular target for the immunosuppressive drugs tacrolimus (FK506) and rapamycin (sirolimus) [NIH]. Upon binding these drugs, FKBPs form inhibitory complexes that target downstream effectors such as calcineurin or the mechanistic target of rapamycin (mTOR), effectively modulating immune responses and cell proliferation [NIH, Wikipedia]. Beyond their role in immunosuppression, various FKBP isoforms are implicated in the pathogenesis of cancer, neurodegenerative diseases, and cardiovascular disorders, where they often serve as critical regulators of proteostasis and potential therapeutic targets [NIH, PubMed].

Other names

Tacrolimus-binding proteinsImmunophilinsPeptidyl-prolyl cis-trans isomerasesPPIases

FKBPs function as intracellular receptors that, upon binding ligands like tacrolimus or rapamycin, form binary complexes that inhibit secondary targets. The FKBP12-tacrolimus complex inhibits calcineurin, a phosphatase required for NFAT dephosphorylation and subsequent T-cell activation. Conversely, the FKBP12-rapamycin complex inhibits the mechanistic target of rapamycin complex 1 (mTORC1), thereby suppressing cytokine-stimulated cell growth and proliferation [NIH, Wikipedia, PubMed].