Ants are eusocial insects that are found in most regions of the world. Within its caste, worker ants are responsible for various tasks that are required for colony maintenance. In their chemical communication, α-helical carrier proteins, odorant-binding proteins, and chemosensory proteins, which accumulate in the sensillum lymph in the antennae, play essential roles in transferring hydrophobic semiochemicals to chemosensory receptors. It has been hypothesized that semiochemicals are recognized by α-helical carrier proteins. The number of these proteins, however, is not sufficient to interact with a large number of semiochemicals estimated from chemosensory receptor genes. Here we shed light on this conundrum by identifying a Niemann-Pick type C2 (NPC2) protein from the antenna of the worker Japanese carpenter ant, Camponotus japonicus (CjapNPC2). CjapNPC2 accumulated in the sensillum cavity in the basiconic sensillum. The ligand-binding pocket of CjapNPC2 was composed of a flexible β-structure that allowed it to bind to a wide range of potential semiochemicals. Some of the semiochemicals elicited electrophysiolgical responses in the worker antenna. In vertebrates, NPC2 acts as an essential carrier protein for cholesterol from late endosomes and lysosomes to other cellular organelles. However, the ants have evolved an NPC2 with a malleable ligand-binding pocket as a moderately selective carrier protein in the sensillum cavity of the basiconic sensillum. CjapNPC2 might be able to deliver various hydrophobic semiochemicals to chemosensory receptor neurons and plays crucial roles in chemical communication required to perform the worker ant tasks.
Keywords: X-ray crystallography; fluorescent competitive binding assay; gas chromatography–electroantennogram detection; molecular evolution; subtraction PCR.