Fig. 1.

The architecture of the M-PTC. (A) NTNHA-A protects BoNT/Ai against trypsin and pepsin digestion when they assemble into the M-PTC in an acidic environment. (B) NTNHA-A protects active BoNT/A against low pH-mediated inactivation. It also protects BoNT/A against trypsin inactivation at pH 6.0, but not at pH 8.0. (C) Cartoon presentation of the M-PTC. BoNT/Ai domains are blue (LC), orange (HN), and green (HC). NTNHA-A domains are yellow (nLC), cyan (nHN), and red (nHC). (D) Individual structures of BoNT/Ai and NTNHA-A in the M-PTC.