DETECTION OF NUISANCE ODORS USING ODOR BINDING PROTEIN SENSOR

Research Synopsis

Nuisance odor control is considered as one of the main reasons why local residents do not want to live near landfills or waste management facilities. However, increasing population and transportation optimization has led to urban solid waste facilities being located closer to populated areas. As a result, more people are now living in close proximity to solid waste management facilities, and the number of odor complaints has also been increasing, resulting in an increased pressure on regulators to introduce more stringent rules. Since the severity of odors cannot be easily quantified, the absence of an effective odor measurement technique creates difficulties for regulatory agencies to draft better rules and provide relief to the general public. To address this problem, researchers at Florida Atlantic University's Laboratories for Engineered Environmental Solutions (Lab.EES) are working on a unique idea developed by Dr. Daniel E. Meeroff. The concept takes inspiration from human biology and how the sense of smell actually works. Researchers at Lab.EES has designed a biosensor that has the potentiality to objectively quantify odors using copies of the human odorant binding protein (hOBPIIa). These are the same proteins that shepherd airborne odorants to the olfactory receptors in the human nose, so that a signal can be sent to the brain that triggers an olfactory response.

Olfaction Science

The figure above shows how humans experience the sense of smell. The odorant binding protein carries the hydrophobic odorant molecules through the mucus lining towards the olfactory receptors. The research is based on this binding principle of the hOBP molecules with the odorants.

Odorant Binding Proteins (OBPs)

Odorant binding proteins (OBPs) are small, soluble extracellular proteins that are found in the nasal mucus of a large variety of animals including insects, pigs, cows, mice, rats, elephants, and humans (Briand et al. 2002; Pelosi 2001). OBPs belong to the lipocalin superfamily that can bind with hydrophobic molecules and are secreted at a high concentration (10 mM) in the nasal epithelium (Heydel et al. 2013). They are known to reversibly bind with volatile chemicals i.e. airborne odorants with micromolar affinities and have dissociation constants in the micromolar range (Briand et al. 2002). They are thought to be good carriers of inhaled odorants towards the olfactory neurons and participate in the selection or deactivation of odorant molecules as well. OBPs have high thermal stability, which is ideal for environmental monitoring.

Image: 3D model of hOBPIIa

Source: proteopedia.org/wiki/index.php/4run

OBPs have recently been used for detecting important ligands in complex environments. In a work by Lu et al. (2014), honeybee OBPs were designed to detect ligands found in floral odors and pheromones. Ramoni et al. (2007) investigated the use of advanced nano-biosensors derived from bOBP (bovine OBP) and immobilized into carbon nanotubes to detect the presence of hazardous compounds in luggage storage facilities, airports, and other public places. The same author also investigated the detection of explosive compounds using the protein scaffold of the lipocalin OBP. However, none of these applications address the challenge of measuring odorant concentrations. Moreover, none of the applications described here use human odorant binding protein (hOBP) for their purpose.

Two possible odor binding protein genes, hOBPIIa and hOBPIIb being 95% identical, have recently been discovered in humans (Briand et al. 2002). The hOBPIIa gene, which codes for the protein hOBPIIa (as shown in the 3D model), has been transcribed in the nasal mucosa. The remarkably large ligand binding cavity inside the β-barrel of hOBPIIa allows it to bind a wide variety of hydrophobic odorants having different structures and sizes with affinities in the micromolar range. Other than this, hOBPIIa has a number of characteristics that qualify the protein to be a good biosensor. hOBPIIa is stable at room temperature, pH, and proteolytic digestion (Whitson and Whitson 2014). Since the protein is non-specific, it can bind with a large number of volatile odorants of different concentrations which is accomplished through the formation of non-covalent bonds (Pelosi 2001). The protein can also be easily manufactured and purified using recombinant bacterial DNA technology at a low cost (Silva et al. 2014). All these characteristics make the human odorant binding protein a viable option to be used in a biosensor application.

References:

Briand, L., Eloit, C., Nespoulous, C., Bézirard, V., Huet, J. C., Henry, C., ... & Pernollet, J. C. (2002). Evidence of an odorant-binding protein in the human olfactory mucus: location, structural characterization, and odorant-binding properties. Biochemistry, 41(23), 7241-7252. https://doi.org/10.1021/bi015916c

Heydel, J. M., Coelho, A., Thiebaud, N., Legendre, A., Bon, A. M. L., Faure, P., ... & Briand, L. (2013). Odorant‐binding proteins and xenobiotic metabolizing enzymes: implications in olfactory perireceptor events. The Anatomical Record, 296(9), 1333-1345. https://doi.org/10.1002/ar.22735

Lu, Y., Li, H., Zhuang, S., Zhang, D., Zhang, Q., Zhou, J., ... & Wang, P. (2014). Olfactory biosensor using odorant-binding proteins from honeybee: Ligands of floral odors and pheromones detection by electrochemical impedance. Sensors and Actuators B: Chemical, 193, 420-427. https://doi.org/10.1016/j.snb.2013.11.045

Pelosi, P. (2001). The role of perireceptor events in vertebrate olfaction. Cellular and Molecular Life Sciences CMLS, 58(4), 503-509. https://doi.org/10.1007/PL00000875

Ramoni, R., Bellucci, S., Grycznyski, I., Grycznyski, Z., Grolli, S., Staiano, M., ... & Conti, V. (2007). The protein scaffold of the lipocalin odorant-binding protein is suitable for the design of new biosensors for the detection of explosive components. Journal of Physics: Condensed Matter, 19(39), 395012

Silva, C., Matamá, T., Azoia, N. G., Mansilha, C., Casal, M., & Cavaco-Paulo, A. (2014). Odorant binding proteins: a biotechnological tool for odour control. Applied microbiology and biotechnology, 98(8), 3629-3638

Whitson, K. B., & Whitson, S. R. (2014). Human odorant binding protein 2a has two affinity states and is capable of binding some uremic toxins. Biochemistry and Analytical Biochemistry, 3(2), 1

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