FKBP52 (also known as FKBP4, Hsp56, FK506 binding protein 4, p52, FKBP59) is a 55kDa peptidyl-propyl isomerase. FKBP52 catalyzes the transition between cis- and trans- proline residues which is important in immunoregulation and proper protein folding and trafficking. FKBP52 may involve in the intracellular trafficking of hetero-oligomeric forms of the steroid hormone receptors.