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15 June 2020 Characterization of Localization, Ligand Binding, and pH-Dependent Conformational Changes of Two Chemosensory Proteins Expressed in the Antennae of the Japanese Carpenter Ant, Camponotus Japonicus
Durige Wen, Xing Li, Xiong Geng, Mitsuhiro Hirai, Satoshi Ajito, Kosuke Takahashi, Mamiko Ozaki, Masaru K. Hojo, Tatsuya Uebi, Tatsuo Iwasa
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Abstract

Camponotus japonicus uses basiconic antennal sensilla (s. basiconica) to sense a colony-specific blend of species-specific cuticular hydrocarbons (CHCs). The inner portion of the s. basiconica is filled with sensillar lymph and chemosensory proteins (CSPs) presumed to transport CHCs to olfactory neuron receptors. Although 12 CSPs have been found in C. japonicus antennae, we focused on CjapCSP1 and CjapCSP13. The molecular basis of CSP1 function was explored by observation of its structure in solution at pH 4.0 and 7.0 through circular dichroism (CD) and X-ray solution scattering. Although the secondary structure did not vary with pH change, the radius of gyration (Rg) was larger by 5.3% (0.74 Å increase) at pH 4.0 than at pH 7.0. The dissociation constant (Kd) for CjapCSP1 measured with a fluorescent probe, 1-N-phenylnaphthylamine, was larger at pH 4.0 than at pH 7.0, suggesting that acidic pH triggers ligand dissociation. In contrast to CjapCSP1, the Rg of CjapCSP13 was slightly smaller at pH 4.0 than at pH 7.0. Western blotting and immunohistochemistry with protein-specific antisera revealed that both CjapCSP1 and CjapCSP13 are detected in the antennae, but differ in their specific internal localization. Binding to four compounds, including the ant CHC (z)-9-tricosene, was examined. Although both CjapCSP1 and CjapCSP13 bound to (z)-9-tricosene, CjapCSP13 bound with higher affinity than CjapCSP1 and showed different binding properties. CjapCSP1 and CjapCSP13 are synthesized by the same cells of the antenna, but function differently in CHC distribution due to differences in their localization and binding characteristics.

© 2020 Zoological Society of Japan
Durige Wen, Xing Li, Xiong Geng, Mitsuhiro Hirai, Satoshi Ajito, Kosuke Takahashi, Mamiko Ozaki, Masaru K. Hojo, Tatsuya Uebi, and Tatsuo Iwasa "Characterization of Localization, Ligand Binding, and pH-Dependent Conformational Changes of Two Chemosensory Proteins Expressed in the Antennae of the Japanese Carpenter Ant, Camponotus Japonicus," Zoological Science 37(4), 371-381, (15 June 2020). https://doi.org/10.2108/zs190138
Received: 14 November 2019; Accepted: 12 March 2020; Published: 15 June 2020
KEYWORDS
(Z)-9-tricosene
cuticular hydrocarbons
nestmate
olfaction
sensilla basiconica
X-ray solution scattering
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