a–c Structural superposition of AcrA and Colicin E3. a AcrA (PDB ID: 5NG5 [https://doi.org/10.2210/pdb5NG5/pdb]). b Colicin E3 (PDB ID: 2B5U [https://doi.org/10.2210/pdb2B5U/pdb]). c Superposition of a, b using Chimera matchmaker93. The RMSD value was 0.85 Å. d, e Model for AcrA-TolC binding. AcrA and TolC structures (PDB ID 5NG5) were used to predict possible modes of their interaction (see “Methods”). d The best models are presented in decreasing order (1–4) of probability. AcrA, all shades of Blue; TolC, gray, brown, and green. e Sideview of the best model (#1). It is physically not very probable for a full-length AcrA (~49 Å diameter) to enter the cell through the TolC pump (~29 Å diameter).