A β‑Turn Motif in the Steroid Hormone Receptor’s Ligand-Binding Domains Interacts with the Peptidyl-prolyl Isomerase (PPIase) Catalytic Site of the Immunophilin FKBP52

The immunophilin FKBP52 interacts with nuclear steroid hormone receptors. Studying the crystal structure of human estrogen receptor α (hERα) and using nuclear magnetic resonance, we show here that the short V364PGF367 sequence, which is located within its ligand-binding domain and adopts a type II β-turn conformation in the protein, binds the peptidyl-prolyl isomerase (PPIase or rotamase) FK1 domain of FKBP52. Interestingly, this turn motif displays strong similarities with the FKBP52 FK1 domain-binding moiety of macrolide immunomodulators such as rapamycin and GPI-1046, an immunophilin ligand with neuroprotective characteristics. An increase in the hydrophobicity of the residue preceding the proline and cyclization of the VPGF peptide strengthen its recognition by the FK1 domain of FKBP52. Replacement of the Pro residue with a dimethylproline also enhances this interaction. Our study not only contributes to a better understanding of how the interaction between the FK1 domain of FKBP52 and steroid hormone receptors most likely works but also opens new avenues for the synthesis of FKBP52 FK1 peptide ligands appropriate for the control of hormone-dependent physiological mechanisms or of the functioning of the Tau protein. Indeed, it has been shown that FKBP52 is involved in the intraneuronal dynamics of the Tau protein.