Fig. 2. Fab structure, derived from PDB file 1HZH, human IgG against HIV-1. This has high structural similarity to trastuzumab Fab, which lacks several key amino acids D224–H227 in PDB; see Fig. S32† which shows mapped on structures. The distances (in Å) from the disulfide bond to either the nitrogen of the lysine or the α-carbon are shown as a guide to proximity, whilst recognizing the high flexibility in the system.