a–c, Superposition of SfLptE with NmLptE (a), NeLptE (b) and SoLptE (c). d, Structure-based sequence alignment of SfLptE with NeLptE, NmLptE and SoLptE. SfLptD, NmLptE, NeLptE and SoLptE are coloured in magenta, orange, cyan and green, respectively. SfLptE, NeLptE, NmLptE and SoLptE represent LptE orthologues from S. flexneri, N. europaea, N. meningitides and S. oneidensis, respectively. Secondary structure elements are labelled on the top. The primary structures of these LptE orthologues have very low sequence identity, but their secondary structure distribution and fold are quite similar.