Chiral recognition mechanism of cellobiohydrolase Cel7A for ligands based on the β‐blocker propranolol: The effect of explicit water molecules on binding and selectivities

Abstract

Proteins are useful chiral selectors. In order to understand the recognition mechanism and chiral discrimination, the binding of the (R)-and (S)-enantiomers of a series of designed amino alcohol inhibitors based on propranolol to cellobiohydrolase Cel7A (Trichoderma reesei) has been studied more closely. X-ray crystal structures were determined of the protein complex with the (R)-and (S)-enantiomers of the strongest binding propranolol analogue. The combination of the structural data, thermodynamic data from capillary electrophoresis and microcalorimetry experiments and computational modelling give a clearer insight into the origin of the enantioselectivity and its opposite thermodynamic signature. The new crystal structures were used in computational molecular flexible dockings of the propranolol analogues using the program Glide. The results indicated that several water molecules in the active site were essential for the docking of the (R)-enantiomers but not for the (S)-enantiomers. The results are discussed in relation to the enantiomeric discrimination of the enzyme. Both dissociation constants (K d values) and thermodynamical data are included to show the effects of the structural modifications in the ligand on enthalpy and entropy in relation to the enantioselectivity.

Update on chiral recognition mechanisms in separation science

“…Fagerström et al. revisited the chiral recognition of an analog of the β‐blocker drug propranolol containing a phenanthrene moiety (Figure 8) by cellobiohydrolase Cel7A using X‐ray crystallography, molecular modeling, thermodynamic and CE data [144]. According to X‐ray analysis, the enantiomers of the analog were bound in a comparable manner and the position of the enantiomers of propranolol and the analog were also almost identical [145].…”

“…By sequential elimination of water molecules and repeated docking, 14 water molecules in the vicinity of the ligand were identified, which influenced the docking of the ( R )‐enantiomer. The authors emphasized that the importance of water molecules in the binding site provided further significant information on the complexation of compounds by cellobiohydrolase Cel7A and may serve as a model system for computational studies of the effect of water molecules on binding and selectivity of protein selectors [144].…”

“…Selected amino acid side chains, the main chain, and water molecules as well as interactions are shown. (Reproduced with permission [144], © by Wiley 2023).…”