A Novel Role for Odorant Binding Proteins in Deactivation of Drosophila Olfactory Neurons

In insects, odorant binding proteins are a large and diverse group of low molecular weight proteins secreted into the fluid bathing olfactory and gustatory dendrites. The best-characterized OBP, known as LUSH, is required in Drosophila melanogaster for the detection of physiological levels of the male-specific pheromone cVA. While LUSH acts as a sensitizing factor for pheromone detection, the role of other OBPs encoded in the Drosophila genome is largely unknown. In an effort to characterize members of this family, I used CRISPR-Cas9 to generate and characterize a deletion of two genes encoding the homologous OBPs OS-E and OS-F. These OBPs are nearly 70% identical and their expression is restricted to a small set of antennal chemosensory sensilla. Electrophysiological analysis of the olfactory neurons within these sensilla revealed no major difference in odorant sensitivity or specificity in the mutants but did reveal a striking deactivation defect to a subset of odorants. Surprisingly, other odorants detected by the same receptor are differentially affected by the absence of OS-E and OS-F, revealing an odorant-specific role for these OBPs in deactivation kinetics. Activation kinetics remain normal for the affected odorants in mutants. Genomic rescue experiments revealed that OS-E and OS-F are also functionally redundant, as either OBP is sufficient to revert the mutant phenotype. My findings reveal a new role for OBPs in deactivation of olfactory neurons and expand our understanding of the range of OBP functions.