Cryo-EM Structure Guided Engineering of Botulinum Neurotoxin A With Advanced Receptor Binding Affinity and Therapeutical Benefits.

Botulinum neurotoxin type A (BoNT/A) has been extensively used in treating a wide range of neurological disorders and aesthetics. However, insufficient binding affinity between BoNT/A and its receptor SV2C could lead to mild to severe side effects. An open active conformation of BoNT/A cryo-EM structure at a resolution of ∼2.85 Å was resolved. Guided by the BoNT/A cryo-EM structure, saturation mutagenesis libraries were constructed and screened by BACTH system to identify mutants that can boost toxin-SV2C affinity. The engineered toxin binding domain achieved up to approximately six-fold improved affinity in SPR analysis, and the engineered toxins exhibited significantly improved binding capacity, and enhanced SNAP25 cleavage efficacy in cultured neurons. Preclinical animal studies, including MLB, DAS, sweat test, and PET/CT assays, demonstrated that the engineered BoNT/A VLTS has higher potency, lower diffusion, and significantly better safety profiles than the BoNT/A wt, which can reduce side effects and benefit future therapeutic applications.