Cryo-EM structures of the cytochrome bc1 complex with metyltetraprole reveals the distinct mechanism of drug resistance

Cytochrome bc1 complex (complex Ⅲ) is one of the most important targets for drug and fungicide discovery. Metyltetraprole (MET) is a novel inhibitor of complex Ⅲ, which has activity against the major reported mutations G143A and F129L of quinone site inhibitor (QoI)-resistant isolates. However, the anti-resistance mechanism of MET is still elusive and very intriguing to be explored. Here, we determined the near-atomic resolution structures of isolated complex III (2.88 Å) and MET-bound complex III (3.26 Å) by cryo-electron microscopy (cryo-EM), showing that MET exhibited a different binding mode from azoxystrobin, a typical QoI. MET could bind to the G143A or F129L mutated complex as well as to the wild-type complex III, whereas the binding affinity of azoxystrobin to the G143A or F129L mutants decreased significantly compared to the wild-type. This work provided a structural basis for the design of the next generation of inhibitors to overcome the resistance.