A 5000-Fold Increase in the Specificity of a Bacterial Phosphotriesterase for Malathion through Combinatorial Active Site Mutagenesis
Figure 3
Docking of malathion into the crystal structures of wild-type PTEAR and PTEAR Ser308Leu/Tyr309Ala.
A. The substrate-binding pocket of PTEAr (2R1N) with bound substrate. The amino acids that were randomised in this experiment are labelled. B. Superimposed structures of malathion docked in the active site of PTEAr in two different conformations. The branched leaving group of malathion results in steric clashes with the protein, primarily with Ser308 and Tyr309. C. Superimposed structures of malathion docked in the active site of the minor, open, conformation of PTEAr in two different conformations. The steric clash with Tyr309 is lessened. D. Superimposed structures of malathion docked in the active site of the Ser309Leu/Tyr309Ala variant of PTEAr. This shows that the Tyr309Ala mutation has opened the substrate-binding cavity, removing the steric hindrance to malathion binding in a productive conformation.