FK506-binding protein 1A (FKBP12)

FK506-binding protein 1A (FKBP12), also known as macrophilin‑12 or tacrolimus binding protein 1A, is a small intracellular immunophilin with peptidyl-prolyl cis-trans isomerase activity. It binds with high affinity to immunosuppressive drugs such as tacrolimus and pimecrolimus. Upon drug binding, the resulting complex inhibits the phosphatase calcineurin in T cells, thereby suppressing immune responses by blocking cytokine production. Beyond its role in immunity, FKBP12 modulates calcium release channels and participates in various cellular processes including signal transduction and protein folding.

Other names

Macrophilin-12Tacrolimus binding protein 1AFKBP-12Immunophilin FKBP12

Drugs such as pimecrolimus and tacrolimus bind to macrophilin‑12/FKBP12, forming a complex that inhibits the phosphatase calcineurin. This blocks T-cell activation by preventing dephosphorylation of NFAT transcription factors and subsequent cytokine gene expression.