Supplementary Figure 7: Mapping the binding sites for CSPG4, FZDs, and bezlotoxumab in TcdB holotoxin.
From: Structure of the full-length Clostridium difficile toxin B
(a) The reported CSPG4-binding site in TcdB, involving residues 1500–1900 (Gupta, P. et al., J Biol Chem. 292, 17290-17301, 2017 and Yuan, P. et al., Cell Res. 25, 157-68, 2015), was colored blue. (b) Binding of TcdB to the immobilized biotin-labeled CRD2 was examined using a pull-down assay at neutral and acidic pH. Samples were analyzed by SDS-PAGE and Coomassie Blue staining. (c) The structure of the cysteine-rich domain of FZD2 (CRD2, green cartoon model) in complex with TcdB1285–1804 (PDB code: 6C0B) (Chen, P. et al., Science, 360, 664-669, 2018) was superimposed to TcdB holotoxin. The pore-forming region of TcdB is shown in a purple ribbon model while the rest of the toxin is shown in a surface model. (d) The structure of the CROPs I–II of TcdB in complex with bezlotoxumab Fabs (PDB code: 4NP4) (Orth, P. et al., J Biol Chem, 289, 18008-21, 2014) was superimposed to TcdB holotoxin. Bezlotoxumab Fabs were shown as cartoon models, which bind to two sites on the CROPs (blue and pink). Bezlotoxumab clashes with the GTD and the DRBD when TcdB adopts the acidic conformation. A close-up view of the boxed area is shown in (e).
