Predicted structures of olfactory receptor proteins modeled against the rhodopsin GPCR, depicting putative ligand-binding pockets between helical transmembrane (TM) domains. a) Schematic depicting an overhead view of the seven transmembrane-spanning barrels of an OR protein. The residues in each helix are numbered separately, according to the predicted TM boundaries. Residues conserved among all GPCRs are shown in open circles. Colored squares and circles represent positions of conserved and variable residues, respectively. Residues that align with ligand contact residues in other GPCRs are colored green and residues that do not align with these residues are colored red. Hypervariable residues (putative odorant-binding residues), which are thought to be under positive selection, are indicated by asterisks. Area II denotes a hypervariable pocket that corresponds to the ligand binding pocket in other GPCRs. Figure modified from . b) Side view of a predicted OR protein structure as seen from within the membrane. Putative OR ligand-binding residues are shown in green and yellow (green : based on homology with non ORGPCR; yellow based on OR evolutionary analysis). Figure from .
Kambere and Lane BMC Neuroscience 2007 8(Suppl 3):S2 doi:10.1186/1471-2202-8-S3-S2