A view of the Orco channel from above, looking down into the pore. When odorant receptor sequences were mapped onto this Orco channel structure, some areas were highly similar, shown in magenta, and other areas were variable, shown in cyan. Most similarities in odorant receptors are concentrated along the central pore, leaving the rest of the protein free to diversify, suggesting how the architecture of this receptor family accommodates its remarkable sequence diversity and facilitates the evolution of odor tuning.