Figure 5

Molecular docking of MBC fungicides to P. xanthii β-tubulins. (A) Surface model of MBC-sensitive β-tubulin showing the predicted binding site for carbendazim (PubChem ID: 25429) located in the region that binds a new tubulin dimer. (B) Surface model of MBC-resistant β-tubulin showing the predicted binding site for diethofencarb (PubChem ID: 91742). (C) Docking results of carbendazim combined with a superposition of MBC-sensitive and MBC-resistant β-tubulin models; carbendazim is proposed to bind MBC-sensitive β-tubulin (cyan) via three hydrogen bonds (dashed lines) that involve residues Thr178 (1: 2.24 Å; 2: 2.49 Å) and Ser138 (3: 2.1 Å). Thr178 is twisted out (arrow) in the MBC resistant β-tubulin model (grey). (D) Docking was also performed using diethofencarb, and it is proposed to bind MBC-resistant β-tubulin (cyan) via two hydrogen bonds (dashed lines) that involve residues Ser138 (1: 1.94 Å) and Tyr222 (2: 2.94 Å). By contrast to observe for carbendazim, diethofencarb cannot bind MBC-sensitive β-tubulin (grey) due to the movement of the Tyr222. (E) Superposition of a model of mammalian β-tubulin model (cyan; PDB ID: 1JFF) in complex with GTP (red) and the P. xanthii β-tubulin model (pink) with carbendazim (green) docked in the proposed MBC fungicide binding site. Alignment results in a high level of coverage between models (grey) and reveals the proximity of the GTP and putative MBC binding sites. Carbendazim binds to β-tubulin via residues 138 (blue) and 178 (purple). (F) As observed upon 90° rotation of the model, residue 198 (yellow) involved in MBC resistance in P. xanthii (the E198A mutation) is located inside of the protein at a position that differs from the proposed MBC binding site).