Fig. 3

Conformation changes induced by the Fe³⁺-enterobactin binding. Apo and complex structures are represented in green and yellow, respectively. a In the extracellular side, the movement of the loop L4 allows Glu327 to interact with Arg100 and push away Glu106 of NL3 that displaces loop NL1. b In the periplasmic side, the N-terminal part of PfeA rearranges following the Fe³⁺-enterobactin binding. The peptide bond of the Pro28 flips resulting in the formation of β-sheet rather the α-helix observed in the apo-structure. In consequence, the TonB box become disordered. T24* refers to the threonine 24 of the complex structure