Fig. 2

ABC holotoxin formation requires a cargo size above a distinct threshold. a Comparison of analytical size exclusion chromatography profiles for ABC holotoxin formed by mixing TcA (600 nM) with TcB-TcC (1.2 μM), separate TcA (600 nM), and separate TcB-TcC(WT) (600 nM). The fractions indicated by the gray bar were pooled and analyzed by EM. b Negative stain electron micrographs of holotoxins formed by TcA and TcB-TcC with the indicated cargos (WT and ICP47 constructs). Insets: 2D class averages of representative TcA pentamers and holotoxins, with the percentages of particles in the class averages shown below. c Negative stain micrographs of holotoxins formed by TcA and TcB-TcC with RBD cargos, with 2D class averages like those described in b. While the cargo HVR45-RBD does not trigger holotoxin formation, the larger HVR128-RBD results in assembled holotoxins. Scale bars in b and c: 100 nm