Positive selection moments identify potential functional residues in human olfactory receptors

Area of Science:

• Molecular biology
• Biophysics
• Sensory neuroscience

Background:

• Olfactory receptors (ORs) detect diverse odor molecules.
• Residues within transmembrane domains are implicated in forming odorant binding pockets.
• Previous studies used mutation analysis and molecular modeling to support this hypothesis.

Purpose of the Study:

• To independently test the hypothesis that transmembrane residues form the OR ligand binding pocket.
• To identify residues in the sixth transmembrane domain (TM6) of human ORs under positive selection.
• To correlate positive selection with potential ligand interaction sites.

Main Methods:

• Calculation of positive selection moments for the TM6 of human olfactory receptors.
• Analysis of identified residues for potential functional roles in ligand binding.
• Comparison with site-directed mutagenesis data from related receptors (e.g., beta-adrenergic receptor).

Main Results:

• Identified specific residues in TM6 likely under positive selection, indicating functional importance.
• Residue 622 (serine or threonine) suggested to form critical hydrogen bonds.
• A dual-serine subsite (residues 622 and 625) proposed to bind hydroxyl groups on odor ligands.

Conclusions:

• The study provides independent evidence supporting the role of TM6 residues in odorant binding.
• Specific residues, particularly 622 and 625, are highlighted as critical for ligand interaction.
• Findings have implications for future research in olfaction, including physiological studies and drug design.