Illustration of the various formats for Antibody (Fragment) or alternative scaffold–drug conjugates. The protein or peptide formats are drawn to scale with an MMAE payload using published Protein Database files (https://www.rcsb.org) as follows: (a) IgG-DAR4, 1igy [12], (b) SIP-DAR2 (modelled on 5c2b [13]), (c) diabody-DAR4, 5fcs [14], (d) Fab-DAR2, 5n2k [15], (e) scFv-DAR8, 5c2b [13], (f) dAb, VH domain-DAR1, 5tsj [16], (g) DARPIn-DAR1, 4j7w [17], (h) Adnectin-DAR1, 3qwr [18], (i) Affibody-DAR1, 1lp1 [19], (j) Knottin-DAR1 1w7z [20], (k) Bicycle-DAR1, 5i8m [21]. The payload used for illustrative purposes is MMAE, 5iyz_4q5 [22] which is hypothetically conjugated to surface residues such as lysines (IgG, Fab, scFv) or C-terminal residues such as cysteine (SIP, Diabody, dAb, alternative scaffolds). The molecular weights indicated are for the protein without payload.