B, Cartoon of the ColE9 OM translocon. ColE9 (orange) exploits the vitamin B12 transporter BtuB (grey) as its extracellular receptor and the porin OmpF (green) for threading its N-terminal IUTD (solid black line) through to the periplasm where it captures TolB (blue). Star, represents the primary site on the ColE9 DNase domain (K469C) where fluorophores were covalently attached throughout this study. 