Peptidyl-prolyl cis-trans isomerase FKBP1B (FKBP12.6)

Peptidyl-prolyl cis-trans isomerase FKBP1B (commonly known as FK506-binding protein 12.6 or FKBP12.6) is a small cytosolic enzyme of the immunophilin family, encoded by the *FKBP1B* gene, that binds immunosuppressants such as FK506 (tacrolimus) and rapamycin (sirolimus)[5]. It acts as a protein folding chaperone with cis-trans peptidyl-prolyl isomerase activity, and selectively associates with the cardiac ryanodine receptor (RyR2), stabilizing its channel function to tune calcium release in the heart[4][5][6]. FKBP12.6 is implicated in the regulation of cardiac calcium dynamics and arrhythmogenesis, and loss of its binding to RyR2 is associated with cardiovascular disease manifestations including arrhythmias and pulmonary hypertension[4][5]. FKBP12.6 is also involved in immunosuppressive mechanisms when complexed with clinical drugs, via inhibition of calcineurin or mTOR pathway signaling[2][3][5].

Other names

FK506-binding protein 12.6FKBP12.6Calstabin2

Inhibits calcineurin when complexed with FK506 (tacrolimus)[2][3][5] Inhibits mTOR when complexed with rapamycin (sirolimus)[2][3][5] Modulates calcium release by stabilizing RyR2 in cardiac muscle[4][6]