Odorant-binding proteins (OBPs) are small (10 to 30 kDa) soluble proteins secreted by auxiliary cells surrounding olfactory receptor neurons, including the nasal mucus of many vertebrate species and in the sensillar lymph of chemosensory sensilla of insects. OBPs are characterized by a specific protein domain that comprises six α-helices joined by three disulfide bonds. Although the function of the OBPs as a whole is not well established, it is believed that they act as odorant transporters, delivering the odorant molecules to olfactory receptors in the cell membrane of sensory neurons. The olfactory receptors of terrestrial animals exist in an aqueous environment, yet detect odorants that are primarily hydrophobic. The aqueous solubility of hydrophobic odorants is greatly enhanced via odorant-binding proteins, which exist in the extracellular fluid surrounding the odorant receptors. This family is composed of pheromone binding proteins (PBP), which are male-specific and associate with pheromone-sensitive neurons and general-odorant-binding proteins (GOBP). These proteins were initially identified on the basis of their ability to bind with moderate-affinity radioactively labeled odorants. Structure OBPs are small proteins on the order of 14 kDa in size. All odorant binding proteins are believed to have a common structure despite their genetic diversity and highly variable primary structures. In vertebrates, OBPs are a part of the lipocalin family. They are structurally characterized by a β-barrel motif composed of antiparallel β-sheets. Insect OBPs share very little amino acid sequence similarity to vertebrate OBPs as they mainly contain α-helical domains. OBPs are divergent across and within species. The percentage of conserved residues between species has been shown to be as low as 8%. OBPs' have a characteristic signature that is recognized by a conserved pattern of six cysteines that are connected in the protein by three disulfide bridges. Their structures have been investigated to explore new bio-inspired repellents against mosquitoes, with potentially improved OBP binding affinity, selectivity, and reduced volatility. Function The functions of odorant binding proteins as a whole is not well understood. They are generally believed to increase the solubility of hydrophobic odorants by binding them and transporting them across the aqueous sensillum lymph to receptors in the dendrites, and several studies support a role for OBPs in olfactory perception in vivo. Some odorant binding proteins are hypothesized to hasten odor response termination by extracting odorant molecules from the sensillar lymph or from receptors themselves. Presently, just one OBP, Obp76a, has been thoroughly investigated in the