Comparison of key residues within the orthosteric binding pocket of planarian 5-HT receptors.

Table shows amino acid identity at indicated residues (column header, B&W nomenclature [28]) in individual S1, S4 and S7 planarian receptors. S1.1 and S4.2 were omitted as transcriptomic sequence represented only partial clones that did not contain the relevant sequence information. Corresponding residues are shown for representative human GpCRs (bottom), including 5-HT receptors. Polarity of residue at 5.42 and 5.46 are highlighted (italics, non-polar; underlined, polar). Residues at 5.42 and 5.46 are thought to be less polar in 5-HT receptors compared with receptors with different bioaminergic specificity. Numeric values depict amino acid spacing between indicated B&W residues: for example, 3.37 and 5.42 are separated by ~74 residues in S7 receptors. Accession numbers used for comparison: 5HTR1B (P28222), 5HTR2B (P41595), 5HTR6 (P50406), DRD3 (dopamine D3 receptor, P35462), ADRB2 (beta-2 adrenoceptor, P07550), HRH1 (histamine H1 receptor, P35367).