Figure 1: Amino acid sequence of the C-terminal repetitive and putative receptor binding domain from C. difficile toxin B (TcdB RBD). (A) The amino acid sequence (537 residues) of TcdB RBD was identified using the online software ( / Tools/pfa/radar/). The localization of the 4 long-repeat (LR) regions of oligossacharide-binding sites are highlighted in red color.