The remodelling of the active site of the designer retroaldolase RA95.0 [14••]. (a) The structure of RA95.0 (PDB code 4A29) showing the designed catalytic lysine residue, Lys210 (yellow) and the 1, 3 diketone mechanism-based inhibitor (green). (b) The structure of variant RA95.5 (PDB code 4A2S) showing the two different binding modes of inhibitor, one using Lys210 (yellow) and the other, the newly introduced Lys83 (orange). (c) The structure of RA95.5-5 (PDB code 4A2R) showing that the active site location has switched during evolution to the new lysine Lys83, and that Lys210 is not modified in RA95.5-5.