Positioning of compound tails is diverse and flexible. The crystal structures, similarly to the docking results (Fig. ), also show that, in contrast to the 2-aminobenzothiazole moieties, the compound tails are conformationally variable, as indicated by the less well defined shapes of their electron density maps (Fig. , SI), and lower occupancies than for the 2aminobenzothiazole cores (50-70% vs. 70-90%, respectively, Tab. S10, SI). In some subunits of some structures, parts of the ligand tails are missing whereas the 2-aminobenzothiazole cores are present (in TbPTR1 complexes with 1a and 2e, Tab. S10, SI). Furthermore, the amide linkers of the compounds adopt either a cis or trans configuration orienting the compound tails in different subpockets of the active site (for the compounds without an additional substituent on amide N, "cis" means placement of 2-aminobenzothiazole and the halogenated phenyl tail on the opposite sides of amide). Despite different orientations of the amide moieties, a conserved water-mediated interaction is always formed with the Asp161 carboxylate and the Gly205 backbone carbonyl (Fig. ).