A, Schematic of the ColE9 sequence showing its constituent domains: an intrinsically unstructured translocation domain (IUTD) at the N-terminus is followed by three structured domains involved in translocation (T), receptor (R) binding and cytotoxicity (C). The IUTD houses three linear protein-protein interaction epitopes, two OmpF binding sites (OBS1, OBS2) flank a TolB-binding epitope (TBE). Residue numbers denote position in ColE9 sequence. 