Fig. 4. Schematic diagram showing the structure of family B GPCRs generated using ClustalW.31 Reprinted with permission from Springer Nature: Springer Nature, Nature Reviews Drug Discovery, Structural diversity of G protein-coupled receptors and significance for drug discovery, M. C. Lagerström and H. B. Schiöth, Copyright (2008). The residues conserved in all 15 sequences are displayed as circles, the conserved polar residues are shown in orange, the aromatic residues in purple, the aliphatic residues in beige, the positively and negatively charged residues are shown in red and blue respectively.31 The uppercase letters show the completely conversed positions, the lowercase letters show the well-conserved positions (>50%) while the letter “x” show the variable positions. The conserved sequence motifs which are found in the TMD of the family B GPCRs are surrounded by red boxes.31 The conserved cysteine residues are depicted as yellow circles, the cysteine bridges between EL1 and EL2 are shown as two straight lines while the N-terminal cysteine bridges are drawn as lines.31.
