Figure 1.

Structure of camelid heavy chain‐only antibodies and nanobodies. (A) Schematic representation of a heavy chain‐only Ab with the structure of the VHH domain (Nb) highlighted. The complementarity‐determining regions (CDRs) are labelled in different colours: CDR1 in yellow, CDR2 in green, CDR3 in blue and the framework regions (FR) are indicated in red. (B) The linear structural diagram of a VHH domain, indicating CDRs, disulfide bonds (S‐S) in the molecule and positions of framework region 2 of VHHs that contain more hydrophilic amino acids (e.g. Y37, E44, R45, G47) compared with conventional VHs (e.g. V37, G44, L45, W47). The conserved canonical S‐S in Ig domains and the additional non‐conserved S‐S found in many Nbs are also illustrated.