著者

WEN Duriga

出版者

室蘭工業大学 (Muroran Institute of Technology)

巻号頁・発行日

2020

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Social insects depend on complex communication systems to maintain their societies, in which individuals may exchange information through pheromones. Ants are one such example of social insects. In many species of ants, even if they are conspecific, nestmates are clearly able to distinguish non-nestmates, which they subsequently reject. This is accomplished with cuticular hydrocarbon (CHC) blends on the ant body that are used in social pheromone nestmate recognition. The Japanese carpenter ant Camponotus japonicus uses basiconic antennal sensilla (s. basiconica) to sense colony-specific blends of species-specific CHCs, which are hydrophobic. Basiconic antennal sensilla are only observed in females and are filled with sensillar lymph. Chemosensory proteins have been shown to be major proteins that are expressed in ant antenna and are thus expected to transport CHCs to the receptor membranes of olfactory neurons. Twelve CSPs were found from the analysis of RNA expression in C. japonicus antennae. In particular, CSP1 in C. japonicus (CjapCSP1) was found to be highly expressed and has been shown to bind to 18 C. japonicus-specific CHCs. We investigated whether CSP1 represents pH-dependent changes in structure and/or ligand-affinity. In addition, we studied CjapCSP13. Both CjapCSP1 and CjapCSP13 are abundantly expressed in worker ant antennae and are coexpressed in some chemosensilla. To understand the functions of CjapCSP1 and CjapCSP13 based on their structures and their structural changes in the solution, X-ray solution scattering measurements, small angle X-ray scattering (SAXS), and wide angle X-ray scattering (WAXS) were performed. The molecular basis of CSP1 function was evaluated from its structure in solution by CD and X-ray solution scattering measurements at pH 4.0 and 7.0. Although the secondary structure did not vary, the gyration radius (Rg) was found to be 5.3% larger (0.74 Å increase) at pH 4.0 than at pH 7.0. The dissociation constant (Kd) of a fluorescent probe, 1-N-phenylnaphtylamine, for CjapCSP1 was larger at pH 4.0 than at pH 7.0, suggesting that this structural change could trigger ligand dissociation at acidic pH. In contrast to the CSP1, the Rg of CjapCSP13 was slightly smaller at pH 4.0 than at pH 7.0. Western blotting and immunohistochemistry with specific antiserums revealed that both CjapCSP1 and CjapCSP13 were detected in antenna, but differed in location. The binding characteristics to four kinds of compounds, including the ant CHCs (z)-9-tricosene, were also examined. Although both CjapCSP1 and CjapCSP13 bound to (z)-9tricosene, CjapCSP13 bound more strongly than CjapCSP1 and showed different binding properties. CjapCSP1 and CjapCSP13 are synthesized in the same cell of the antenna, but they function differently in the CHC reception due to differences in their localization and binding characteristics.