Panel A shows the predicted binding modes of the dual H4R/5-HT3AR hit 8 (green carbon atoms, see for molecular structure) in structural models of H4R and 5-HT3AR. Parts of the backbone of transmembrane (TM) helices 3, 5, 6 and 7 (the top TM3 is not shown for clarity) in H4R and loops A, B, C and E of the extracellular ligand-binding domain (ECD) of 5-HT3AR are represented by light yellow ribbons. Important binding residues are depicted as ball-and-sticks with grey carbon atoms. Oxygen, nitrogen, and hydrogen atoms are colored red, blue, and cyan, respectively. H-bonds described in the text are depicted by black dots. The molecular interaction fingerprint (IFP) bit strings of 8 in H4R and 5-HT3AR are compared in panel B.