Inhibitory antibodies mAb926 and mAb475 recognize epitopes differently overlapping the mannose-binding pocket of FimH.

Epitope of mAb926 mapped on crystal structure of the active (A) and inactive (D) conformations of the FimH lectin domain. Cα atoms of mAb926 epitope residues are shown as blue spheres. The natural allosteric site (residues V28, V30, S114 and A115)[11] is shown as grey spheres and D-mannose is shown as red sticks. The epitope of mAb21 is shown as magenta spheres. (B and E) Close-up of FimH binding pocket with mAb926 and mAb475 epitopes presented as colored sticks. The mAb926 epitope is shown in blue and mAb475 epitope is shown in yellow. The overlapping residues of these two epitopes are shown in green. D47 residue, involved in direct hydrogen bond with D-mannose but not being a part of either mAb epitope is shown as grey sticks. (C and F) Relative distances between mannose-contacting amino acid residues in the active and the inactive FimH conformations, respectively. The crystalized and the computationally docked (see text) positions of D-mannose (red sticks) are also shown. The presented distances were measured between heavy atoms of residue side chains that are known to form hydrogen bonds with D-mannose ligand [38]. The PDB codes for active- and the inactive structures are 1UWF and 3JWN, respectively. The position of D-mannose in the 1UWF was determined by alignment with the sugar ring of butyl α-D-mannoside of the original crystal structure.