DyBOBS: A Dynamic Biomimetic Assay for Odorant-Binding to Odor-Binding Protein

Current and potential biotechnological applications of odorant-binding proteins

Odorant-binding proteins (OBPs) are small soluble proteins whose biological function is believed to be facilitating olfaction by assisting the transport of volatile chemicals in both vertebrate and insect sensory organs, where they are secreted. Their capability to interact with a broad range of hydrophobic compounds combined with interesting features such as being small, stable, and easy to produce and modify, makes them suitable targets for applied research in various industrial segments, including textile, cosmetic, pesticide, and pharmaceutical, as well as for military, environmental, health, and security field applications. In addition to reviewing already established biotechnological applications of OBPs, this paper also discusses their potential use in prospecting of new technologies. The development of new products for insect population management is currently the most prevailing use for OBPs, followed by biosensor technology, an area that has recently seen a significant increase in studies evaluating their incorporation into sensing devices. Finally, less typical approaches include applications in anchorage systems and analytical tools. KEY POINTS: • Odorant-binding proteins (OBPs) present desired characteristics for applied research. • OBPs are mainly used for developing new products for insect population control. • Incorporation of OBPs into chemosensory devices is a growing area of study. • Less conventional uses for OBPs include anchorage systems and analytical purposes. Graphical Abstract.

Real-time monitoring of the metabolic capacity of ex vivo rat olfactory mucosa by proton transfer reaction mass spectrometry (PTR-MS)

Olfactory mucosa (OM) can metabolise odorant volatile organic compounds through various enzymatic mechanisms to produce odorous or non-odorous metabolites. Preliminary ex vivo studies using headspace-gas chromatography (HS-GC) revealed the formation of metabolites when odorant molecules were injected in the headspace above a fresh explant of rat olfactory mucosa. However, this method did not allow accessing the data during the first 5 min of contact between the odorant and the mucosa; thus limiting the olfactory biological significance. Using a direct-injection mass spectrometry technique with a proton transfer reaction instrument (PTR-MS), we have been able, for the first time, to investigate the first moments of the enzymatic process of the metabolic capacity of ex vivo rat olfactory mucosa in real time. Using ethyl acetate as a model volatile odorous substrate, we demonstrated here for the first time that this odorant could be metabolised by an ex vivo olfactory mucosa within seconds, producing ethanol as metabolite.

Dynamics of odorant binding to thin aqueous films of rat-OBP3

Uptake, retention and release of 5 selected odorants (benzaldehyde, 2-methylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-isobutylthiazole, and 2,4,5-trimethylthiazole) by recombinant rat odor-binding protein 3 (rat-OBP3) were measured in a model system under nonequilibrium conditions. Gaseous odorants were introduced into a 100 mm section of a polar deactivated capillary in which aqueous rat-OBP3 films were formed to mimic the olfactory epithelium (OE), and the change in the gas-phase concentration of the outflow gas was monitored in real time using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). The 5 odorants were chosen because they exhibited a broad range of dissociation constants with rat-OBP3 and because they were amenable to detection by on-line APCI-MS. All 5 odorants were quantitatively bound by rat-OBP3, which resulted in an effective concentration of the odorants in the aqueous layer (about 50 000-fold). Odorant release from the rat-OBP3-odorant complex into the gas phase showed that odorant release was governed by the dissociation constant of the complex and the flow rate of odorant-free air. When 2 odorants were introduced into the system, odorant uptake and release were influenced by the method of introduction and their relative affinities for the protein. Because rat-OBP3 exhibits typical odorant-binding characteristics, the results not only provide fundamental information on the kinetics of odorant mass transfer induced by the presence of OBPs in the olfactory mucus layer but also support the possibility that vertebrate OBPs may facilitate the accumulation of odorants in the OE.