Sequence logos of short sections of aligned receptors in key positions that are involved in ligand recognition, binding and receptor functionality for the human OTR as well as residues found in contact with the ligand, obtained from the GPCR ligand co-crystal after structural super-positioning, are shown (Supplementary Table S1 at http://www.biochemsoctrans.org/bst/041/bst0410197add.htm). The sections (solid boxes) include the N-terminal residue Arg³⁴ (a), Asp⁸⁵ in TM1 (b) in TM2 (c), Phe¹⁰³ in the ECL (extracellular loop) 1 (d), TM3 (e), ECL2 (f), Tyr²⁰⁹ in TM5 (g), Lys²⁷⁰ in ICL3 (h), Phe²⁸⁴ in TM6 (i) and TM7 (j). Numbering of residues is based on the human OTR sequence. Residue positions of importance, on the basis of previous biochemical studies, are highlighted by grey boxes and OT receptor residues are highlighted in red. Common GPCR–ligand interacting residues (highest frequency show residues Gln¹¹⁹, Met¹²³, Ile²⁰⁴, Val²⁰⁸, Trp²⁸⁸, Phe²⁹¹, Phe²⁹², Gln²⁹⁵ and Met³¹⁵; numbering according to human OTR; Figure 3 and Supplementary Table S1) are labelled with an asterisk and residues that correlate with the respective ligand sequence (i.e. Ile⁴⁹, Leu⁹⁸, Ile²⁰⁴ and Val²⁰⁸; numbering according to human OTR) are coloured in blue.