FKBP1B is a member of the immunophilin protein family, which play a role in immunoregulation and basic cellular processes involving protein folding and trafficking. This protein is a cis-trans prolyl isomerase that binds the immunosuppressants FK506 and rapamycin. The protein is highly similar to the FK506-binding protein 1A. Its physiological role is thought to be in excitation-contraction coupling in cardiac muscle.