Figure 4. Candidate protein-altering SNPs on chemosensory protein models.

Protein model templates for the four chemosensory families onto which residues identified as selection candidates (top 1% F_st) are mapped. The colour coding (bottom right box) indicates the number of times a particular residue was identified as a candidate in pair-wise population comparisons. Although monomeric proteins are shown, IRs and ORs form heteromeric complexes of ligand-tuning receptors with structurally related co-receptors⁶, and GRs are also likely to function in multimeric assemblies¹⁶. Double-headed arrows next to these protein models indicate the approximate position of the sensory neuron membrane. IR: residues are mapped onto the X-ray crystal structure of the AMPA iGluR (PDB 3KG2). The IR amino-terminal region is much shorter and highly divergent from that of iGluRs, leading to very poor alignment quality, so the precise three-dimensional position of the mapped residues in this region is not informative. OR: residues are mapped onto the OR85b model built by amino-acid coevolutionary and secondary structure analyses⁴¹. The large dark-grey spheres on the OR structure highlight the location of residues experimentally implicated in influencing ligand recognition properties. We have excluded the high F_st residues for OR22b and OR22c due to the complex nature of the locus (polymorphic chimeric). GR: residues are mapped onto a snake plot of GR10b, as no three-dimensional information is available. OBP: residues are mapped onto the LUSH (OBP76a) structure (PDB: 2GTE). The green sphere indicates the internal cavity where the ligand is expected to reside.