Peptidyl-prolyl cis-trans isomerase FKBP1A (FKBP12) (FKBP12)

Peptidyl-prolyl cis-trans isomerase FKBP1A, commonly known as FKBP12, is a highly conserved 12 kDa cytosolic protein that belongs to the immunophilin family [1]. It functions as a molecular chaperone, utilizing its peptidyl-prolyl isomerase activity to catalyze the folding of proteins by facilitating the rotation of proline imidic peptide bonds [1][2]. Beyond its enzymatic role, FKBP12 is a crucial regulator of intracellular signaling complexes, such as the ryanodine receptor (RyR), where it stabilizes the channel to prevent calcium leakage in muscle cells [3][4]. In pharmacology, FKBP12 is a quintessential drug target that operates through a unique gain-of-function mechanism [5]. It forms high-affinity complexes with drugs like tacrolimus and sirolimus; the tacrolimus-FKBP12 complex inhibits calcineurin to block T-cell activation, while the sirolimus-FKBP12 complex inhibits the mTORC1 pathway to halt cell proliferation [5][6][7]. Consequently, FKBP12 is central to the clinical management of organ transplant rejection and the treatment of various malignancies [6][7]. It also modulates the TGF-beta signaling pathway by interacting with type I receptors to maintain them in an inactive state in the absence of a ligand [8].

Other names

FK-506 binding protein 12FKBP1AFKBP-12FK506-binding protein 1Immunophilin FKBP12PPIase FKBP1A12 kDa FK506-binding protein

FKBP12 acts as a mandatory co-receptor for several immunosuppressive and anti-proliferative drugs; it forms a binary complex with tacrolimus to inhibit the phosphatase calcineurin, or with sirolimus (and its analogs) to inhibit the mechanistic target of rapamycin complex 1 (mTORC1) [5][6][7].