Olfactory Receptor Proteins - Bioelectronic Nose: Integration of Biotechnology and Nanotechnology - page 54

Fig. 3.2 Multiple sequence alignment of the 7 transmembrane helices for the 17 GPCRs whose
3D structure has been experimentally solved

the amino acid residue contacts the ligand in all known GPCR 3D structures [ 34 ].
They found that residues at positions 3.32, 3.33, 3.36, 6.48, 6.51 and 7.39 (Balles-
teros-Weinstein nomenclature), irrespective of their type, always establish contacts
with the ligand. Among these consensus positions, two pairs of positions (3.36-6.46
and 6.51-7.39) are also present in the network of conserved TMH contacts that
maintain the helical bundle scaffold. They dubbed the latter positions the “ligand-
binding cradle”.

3.3 Signal Transduction Mechanisms

To date, only three structures of GPCR in an activated conformational state are
available: rhodopsin in a complex with the C-terminus peptide of the α-subunit
of the transducin G protein [ 35 , 36 ], β2 adrenergic receptor in a ternary complex
with an agonist and a camelid antibody fragment (nanobody) that mimics G protein
behavior [ 29 ] and the same agonist-receptor system in complex with the whole
heterotrimeric Gs protein [ 30 ]. A number of other structures in which the receptor