Crystal Structure of Colicin E3 Sandriyana Soelaiman, Karen Jakes, Nan Wu, Chunmin Li, Menachem Shoham  Molecular Cell  Volume 8, Issue 5, Pages 1053-1062 (November 2001) DOI: 10.1016/S1097-2765(01)00396-3

Figure 1 Schematic Representation of the Mechanism of Action of Colicin E3 T, translocation domain; R, receptor binding domain; C, catalytic domain; IP, immunity protein to colicin E3. Molecular Cell 2001 8, 1053-1062DOI: (10.1016/S1097-2765(01)00396-3)

Figure 2 Ribbon Diagrams (A) The colicin E3-IP complex is Y shaped with dimensions of 75 × 135 × 45 Å. (B) Close-up of the jellyroll structure of the translocation domain in the same orientation as in (A). The three β sheets are shown in red, blue, and yellow. The β strands are numbered consecutively from the N terminus. The β barrel is flanked by two α-helical stretches. The second and longer α helix ends with P315, which causes a kink in the helix and leads directly into the helical receptor binding domain. (C) Close-up of the catalytic domain and the IP. The C domain is shown in gray and the IP in red. Catalytic residues are shown in ball-and-stick. This orientation shows that the two β sheets are roughly perpendicular to each other. Molecular Cell 2001 8, 1053-1062DOI: (10.1016/S1097-2765(01)00396-3)

Figure 3 The Receptor Binding Domain (A) The R domain forms an Alacoil (Gernert et al., 1995), an antiparallel coiled coil in which every seventh residue is a core alanine. The two helical segments are vertically offset by half a repeating unit such that the core alanine residues alternate between the two helices. Core alanine residues are depicted in ball-and-stick. The lower part of the R domain is rich in hydrophobic residues, in particular, in and around the hairpin. These hydrophobic moieties, which are candidates for the interaction with the BtuB receptor, are labeled and shown in ball-and-stick. (B) Docking of the R domain of colicin E3 onto the binding pocket of a model of the BtuB receptor built by homology to FhuA (Locher et al., 1998). The hairpin of the R domain penetrates the binding pocket to a depth of 25 Å. Molecular Cell 2001 8, 1053-1062DOI: (10.1016/S1097-2765(01)00396-3)

Figure 4 Surface Representation Colicin E3 is shown in white, the IP in magenta, and the active site of the RNase domain in cyan. (A) The binary colicin E3-IP complex. (B) IP is removed from the complex. Eighty-three percent of the IP surface is buried by the interaction with both globular domains of colicin E3. The IP does not block the active site of colicin E3. It presumably prevents access of the RNase domain to its huge substrate, the ribosome. Molecular Cell 2001 8, 1053-1062DOI: (10.1016/S1097-2765(01)00396-3)

Figure 5 Comparison of the Crystal Structures of Colicins E3 and Ia Colicin E3 is shown in blue, IP in red, and colicin Ia in green. The coiled coil regions in both proteins were superimposed to create this figure. While a stretch of about 100 residues corresponding to the coiled coil regions in both proteins has the same fold, the rest is very different in these two colicins. Molecular Cell 2001 8, 1053-1062DOI: (10.1016/S1097-2765(01)00396-3)