(a) Views of the atomic resolution structure of ErpC with the secondary structure shown in cartoon representation. The main chain is coloured from the N-terminus (blue) to the C-terminus (red). Loops that were not observed in the crystal structure are represented as dotted lines. This figure was generated using PyMOL v.184.108.40.206 (Schrödinger). (b) Stereoview of representative electron density around the N-terminal α-helix (residues 99–110). A 2Fo − Fc σA-weighted map contoured at 0.1353 e Å−3 is shown. (c) Representations of the charge density on the surface of ErpC calculated using APBS (Baker et al., 2001).