Chemosensory proteins of the eastern honeybee, Apis cerana: Identification, tissue distribution and olfactory related functional characterization.

Chemosensory proteins (CSPs), a class of small soluble proteins, are thought to be involved in insect chemoreceptive behavior. Here, six CSP genes, AcerCSP1-6 from Apis cerana, were cloned and characterized from worker bees' antennae. Results revealed that the AcerCSPs' amino acid sequences shared high similarity with the homologous genes of Apis mellifera, but low similarity with other insect species. Compared with corresponding CSPs of A. mellifera, AcerCSPs (1, 3, 4, and 6) exhibit quite similar gene expression profiling. On the contrary, AcerCSP2 showed a higher expression level in the forager antennae and legs than CSP2 of A. mellifera. Furthermore, AcerCSP5 was not specifically expressed in larvae, unlike CSP5 of A. mellifera. In a ligand-binding assay, AcerCSP1 and AcerCSP2, which exhibited the highest expression in antennae of A. cerana, had a stronger affinity with candidate floral chemicals and pheromones than AcerCSP4, the results of which was supported by docking analysis, suggesting that the relevance of them with A. cerana olfactory functions. Taken together, these results suggest that despite the quasi-similarity of protein sequences between A. cerana and A. mellifera, differences in tissue expression and functional characteristics between the two species still exist, indicating that homologous proteins potentially perform different tasks even in related species.