Divergence from conserved residues underlies intracellular retention of mammalian odorant receptors

Mammalian odorant receptors are a diverse group of G-protein coupled receptors abundantly expressed in the olfactory cilia membrane. The vast majority of odorant receptors show little or no cell surface expression in non-olfactory cells due to endoplasmic reticulum retention, which has slowed down biochemical and functional studies. Here we show that engineered odorant receptors based on consensus amino acids exhibit high levels of cell surface expression that surpass any native odorant receptors. Using a combination of large-scale screening of odorant receptors for cell surface expression in heterologous cells, amino acid sequence analysis and machine learning techniques, we identified amino acid positions scattered throughout the receptor structure that are critical for odorant receptor trafficking. We demonstrated the importance of conserved residues by synthesizing consensus odorant receptors that show similar levels of cell surface expression with conventional G protein-coupled receptors. Furthermore, we associated in silico structural instability with poor cell surface expression using molecular dynamics simulations. Our results highlight the importance of conserved residues in complex regulation of odorant receptor trafficking.