Abstract
Odorant-binding proteins (OBPs) are extracellular proteins found in insect chemosensilla, where they participate in the sensing of odors, tastes, and pheromones. Although a large number of OBP genes have been identified in insect genomes, their molecular functions and biological roles have been clarified in limited cases. Two OBP genes, Obp57d and Obp57e, were involved in the evolution of host-plant preference in Drosophila sechellia. Comparative analyses of the Obp57d/e genomic sequences from 27 closely related species suggested that the two genes arose by tandem gene duplication and functionally diverged from each other. In this study, the functional evolution of Obp57d and Obp57e was examined by in vitro binding assays using recombinant proteins synthesized in a bacterial system. Compared to the ancestral Dpse\\OBP57de, Dmel\\OBP57d was more specialized to tridecanoic acid while Dmel\\OBP57e was generalized regarding their binding affinity, suggesting that the two OBP genes underwent subfunctionalization and neofunctionalization. A behavioral analysis using knockout flies supported that the biological role is different between OBP57d and OBP57e in vivo. Site-directed mutagenesis of the evolutionarily conserved amino acids revealed that these residues play an important role in protein folding. These findings provide a clue to understanding how the repertoire of OBP genes is maintained in a genome under natural selection.
Highlights
In insects, olfaction and gustation play an important role in the detection of foods, egg-laying substrates, mates and predators
These studies successfully demonstrated that an integrated approach using both in vitro and in vivo analyses is required for a thorough understanding of the biological roles of odorantbinding proteins (OBPs)
Expression and purification of recombinant OBPs in E. coli Several methods have been used for the expression of recombinant OBPs in the E. coli system
Summary
Olfaction and gustation play an important role in the detection of foods, egg-laying substrates, mates and predators. Besides the receptors, odorantbinding proteins (OBPs) function in the peripheral chemosensory system of insects by interacting with chemical compounds at the initial step of perception. In the case of a Drosophila OBP, LUSH (OBP76a), the integrated analyses of behavioral genetics, protein crystallography, and electrophysiology showed that the conformational change of LUSH protein on binding to cisvaccenyl acetate is necessary for activation of the corresponding receptor, OR67d [15].
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