Figure 5. Protein structure models of an IgG-binding domain (C2) from Protein G (blue) in complex with the Fc-region of human IgG (grey).

(A) The two lysine residues located on the α-helix of the IgG-binding domain (marked in red) have each been modified with the BHHTEGST (green)-Eu³⁺ (red ball) complex, resulting in unfavorable steric interactions in these models. (B) 90° view.