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Schematic representations of the interactions between streptavidins and biotin analogs. (A) Natural streptavidin and biotin. (B) Natural streptavidin and 2-iminobiotin. (C) Stv-A23D27 and biotin. (D) Stv-A23D27 and 2-iminobiotin. Amino acid residues surrounded by a rectangle and an ellipse refer to those involved in hydrogen bonding and van der Waals interactions, respectively, with the ligand. These notations are based on Fig. 3 in ref. 12.
