Fig. 2.

Recognition of the antiparallel APH homodimeric CC by nanobodies Nb26 and Nb49. (A) Nb26 (blue) binds to the APH₂ (red) epitope centered around W24_f residue (represented in black sticks) using three CDR loops. The APH N and C termini are marked with dots. Nanobody interactions with APH₂ are shown schematically on the CC surface lattice with different colors corresponding to the CDR loops. APH residues mediating hotspot interactions are highlighted by the red squares. (B) In the structure of the Nb49₂-APH₂ complex, the Nb49 (gray) is positioned parallel to the axis of APH₂ (red), which allows additional interactions with the nanobody framework residues (non-CDR interactions). Interactions mediated by non-CDR residues are shown in brown.