NTNH protein: more than a bodyguard for botulinum neurotoxins.

As one of the most fatal substances, botulinum neurotoxins (BoNTs) have never acted solo to accomplish their formidable missions. Most notably, nontoxic nonhemagglutinin (NTNH), a protein co-secreted with BoNT by bacteria, plays critical roles to stabilize and protect BoNT by tightly associating with it to form the minimal progenitor toxin complex (M-PTC). A new cryo-EM structure of the M-PTC of a BoNT-like toxin from Weissella oryzae (BoNT/Wo) reveals similar assembly modes between M-PTC/Wo and that of other BoNTs, yet also reveals some unique structural features of NTNH/Wo. These findings shed new light on the potential versatile roles of NTNH during BoNT intoxication.