Peptidyl-prolyl cis-trans isomerase FKBP1A (FKBP12) and related FKBP isoforms (FKBP)

Peptidyl-prolyl cis-trans isomerase FKBP1A, commonly known as FKBP12, is a member of the immunophilin family that functions as a molecular chaperone and an enzyme catalyzing the folding of proline-containing proteins [UniProt: P62942]. It is the primary intracellular target for the immunosuppressive drugs tacrolimus (FK506) and rapamycin (sirolimus), which bind to the same hydrophobic pocket of the protein [PubMed: 1703438]. These drugs act through a gain-of-function mechanism where the drug-FKBP12 complex inhibits downstream signaling molecules: the tacrolimus complex inhibits calcineurin to block T-cell activation, while the rapamycin complex inhibits the mechanistic target of rapamycin (mTOR) to suppress cell growth [PubMed: 7530333]. Other isoforms, such as FKBP51 and FKBP52, are involved in regulating steroid hormone receptor sensitivity and are implicated in stress-related psychiatric disorders and oncology [PubMed: 22908290]. Furthermore, FKBP12 and its isoform FKBP12.6 play essential roles in stabilizing ryanodine receptors, thereby regulating calcium release in cardiac and skeletal muscles [PubMed: 10601309].

Other names

FK506-binding protein 1AFKBP12FKBP-12PPIase FKBP1AFKBP1FKBP12.6 (FKBP1B)FKBP51 (FKBP5)FKBP52 (FKBP4)

FKBP ligands act by forming a ternary complex where the drug-FKBP unit binds and inhibits a target protein, such as calcineurin or mTORC1, or by modulating the activity of associated proteins like ryanodine receptors or steroid hormone receptors.