Figure 3 Structures of CsA (A) and FK506 derivatives (B). The immunosuppressive drug CsA contains nine non-proteinogenic amino acids and four N -methylated peptide bonds. Residues 9 to 2 are important for cyclophilin binding (green) and 7 to 4 for interaction with calcineurin (yellow). The calcineurin binding region of FK506 is also indicated in yellow and the FKBP binding region in