Possibility for detecting 14 typical odorants occurring in drinking water by employing human odor-binding protein OBP2a

Odor issues occurring in drinking water have been a big challenge to face for water suppliers globally, which highly commend to develop quick or on-site odor detection tools for the management of odor problems. Olfactory sensors based on odor-binding proteins (OBPs) have been utilized to analyze pollutants in food and air samples, while their application for the detection of typical odor-causing compounds in drinking water is rarely reported, partly due to the lack of knowledge about the binding properties of odorants. In this study, the binding affinity and mechanism of human odor-binding protein OBP2a to 14 typical odorants in water were first assessed using fluorescent competitive binding assays and molecular docking techniques. The 14 odorants include 7 aldehydes, 2 terpenes, 2 thioethers, bis(2-chloro-1-methylethyl) ether (DCIP), 2-ethyl-4-methyl-1,3-dioxolane (2E4MDL), and 2-isobutyl-3-methoxypyrazine (IBMP). The results showed that OBP2a could bind to 9 odorants (K_i = 29.91 μmol/L–48.36 μmol/L), including IBMP, 2-MIB, and six aldehydes (hexanal, heptanal, benzaldehyde, 2-octenal, decanal, and β-cyclocitral), among which stronger binding affinity for aldehydes is observed (K_i = 29.91 μmol/L–43.87 μmol/L). Molecular docking confirmed that Lys112 and Phe97 are major amino acid residues involved in the binding of the most target odorants. To be specific, IBMP and aldehydes can form hydrogen bonds with Lys112; aromatic ring-containing odorants such as IBMP and benzaldehyde can also form pi–pi stacking with Phe97. The binding affinity of OBP2a to fatty aldehydes including hexanal, heptanal, 2-octenal, decanal, and β-cyclocitral increased with the increase of hydrophobicity of aldehydes. The valuable information to the binding of OBP2a to typical odorants in this study would provide a theoretical foundation for the development of OBP-based odor detection biosensors to achieve quick detection in drinking water, further helping the improvement of water treatment processes in the water industry.

Graphical Abstract