New insights on the adsorption of floral odorants on Apis cerana cerana olfactory receptor AcerOr1: Theoretical modeling and thermodynamic study.

Apis cerana cerana counted on its sensitive olfactory system to make survival activities in the surrounding environment and the olfactory receptors can be considered as a primary requirement of odorant detection, recognition and coding. Indeed, the exploitation of the olfactory system of insects in particular the Asian honeybee "Apis cerana cerana" can be the best experimental model to investigate the essentials of the chemosensitivity and may help to better understand the olfactory perception in insects. Hence, an advanced statistical physics modeling via the monolayer model with single energy (n ≠ 1) of the three dose-olfactory responses curves indicated that undecanoic acid, 1-octyl alcohol and 1-nonanol were docked with a mixed parallel and non-parallel orientation on AcerOr1. Furthermore, in the present work, the Apis cerana cerana olfactory receptor AcerOr1 showed high sensitivity and discrimination power to detect undecanoic acid, 1-octyl alcohol and 1-nonanol with concentrations at half saturations values of 10-7 mol/L and the molar adsorption energy values obtained from data fitting results, which were ranged from 17.91 to 24.00 kJ/mol, confirmed the exothermic and the physisorption nature of the adsorption of the studied floral odorants on AcerOr1. The studied experimental dose-response curves of undecanoic acid, 1-octyl alcohol and 1-nonanol provided access to quantitative (i.e., stereographic and energetic) characterizations of AcerOr1 via the determination of the olfactory receptor site size distributions (RSDs) and the adsorption energy distributions (AEDs). The stereographic characterization showed RSDs spread out from 0.20 to 8 nm presenting average values corresponding to the maximum of the peaks at 1.50 nm, at 1.10 nm and at 1.04 nm for undecanoic acid, 1-octyl alcohol and 1-nonanol, respectively. The energetic characterization presented AEDs ranged from 0 to 40 kJ/mol showing an approximate adsorption energy bands defined between 7.50 and 27.50 kJ/mol, between 15 and 33 kJ/mol and between 13.50 and 34.50 kJ/mol for undecanoic acid, 1-octyl alcohol and 1-nonanol, respectively. The utilization of the analytical expression of the olfactory threshold allowed giving important and helpful informations about the occupation rate of AcerOr1 binding sites that fired a minimal olfactory response at a honeybee olfactory receptor. Hence, the olfactory response can be detected only when 1.97 %, 1.13 % and 2.00 % of AcerOr1 binding sites were occupied by undecanoic acid, 1-octyl alcohol and 1-nonanol, respectively. Lastly, by means of the selected model, the thermodynamic potentials, such as the adsorption entropy, the Gibbs free enthalpy and the internal energy could be calculated and interpreted.

Advanced investigation of a putative adsorption process of nine non key food odorants (non-KFOs) on the broadly tuned human olfactory receptor OR2W1: Statistical physics modeling and molecular docking study.

In the present paper, statistical physics formalism was used to understand the olfactory perception via the investigation of dose-olfactory response curves of a putative adsorption process of nine non key food odorants (non-KFOs) on the broadly tuned human olfactory receptor OR2W1, in order to quantitative characterize the interactions between the nine studied non-KFOs, i. e., furfuryl sulfide, furfuryl disulfide, benzyl methyl disulfide, furfuryl methyl disulfide, benzyl methyl sulfide, 1-phenylethanethiol, benzyl mercaptan, furfuryl methyl sulfide and 3-phenylpropanol molecules and OR2W1 binding sites at a molecular level. Two advanced adsorption models have been proposed: the advanced monolayer monoenergy model (monolayer model with identical and independent olfactory receptor binding sites) (Model 1) and the advanced monolayer model with two independent types of olfactory receptor binding sites (Model 2). It was concluded that the monolayer monoenergy model was selected as the most adequate model to fit the experimental dose-olfactory response curves tabulated in literature. Actually, the numerical values of the three fitted physico-chemical parameters (RM1, n and C1) were obtained by a non-linear regression. Indeed, modeling results suggested that the number of docked non-KFOs per OR2W1 binding site n values (1.24 < n < 1.94) was always superior to 1, which indicated the non-parallel orientation of the studied odorants on the olfactory receptor and the multi-molecular adsorption mechanism. The estimated molar adsorption energy ΔEa values (ranged from 6.07 to 12.16 kJ/mol) for the nine olfactory systems confirmed the physical the exothermic characters of the adsorption process since ΔEa values were lower than 40 kJ/mol and positive. Furthermore, these estimated parameters were applied to characterize stereographically and energetically the interaction between the nine non-KFOs and OR2W1 through the determination of the human receptor binding site size distributions (RSDs) and the adsorption energy distributions (AEDs), which were spread out from 0.25 to 6.50 nm and from 0 to 22.50 kJ/mol, respectively. The docking computation between these nine non-KFOs and OR2W1 proved that the estimated binding affinities were belonged to the adsorption energies spectrum in general and the specific adsorption energy band or the molecular vibration modes limited spectrum (between 2.50 kJ/mol and 17 kJ/mol) (approximate olfactory band).

Theoretical study of the olfactory perception of floral odorant on OR10J5 and Olfr16 using the grand canonical ensemble in statistical physics approach.

In this work, two experimental dose-response curves of lyral molecules on the OR10J5 and the Olfr16 were employed in order to examine the evolution of physico-chemical parameters involved in the selected statistical physics model(s) to investigate the human and the mouse smelling of a floral scent. Indeed, one layer adsorption model on one type of sites with one energy (1LAM1T1E) and one layer adsorption model on two types of sites with two energies (1LAM2T2E), considered as appropriate models for the adsorption of lyral molecules on the OR10J5 and Olfr16, respectively, have been applied to fit the experimental data. Stereographic and energetic physico-chemical parameters, namely: the maximum response(s) at saturation, the number of docked molecules per olfactory receptor binding site and the concentration(s) at half saturation, were investigated to retrieve helpful information to describe the adsorption process putatively introduced in the olfaction perception. Thus, the advanced modeling results indicated that the studied molecules were docked with a non-parallel orientation (n > 1). Furthermore, for the two olfactory systems, the molar adsorption energies estimated from curves modeling were inferior to 11 kJ/mol, which showed the physisorption process of the adsorption of lyral molecules on OR10J5 and Olfr16. The 1LAM2T2E and the 1LAM1T1E were applied to estimate the OR10J5 and the Olfr175 RSDs, respectively. Hence, lyral RSDs were spread out from 0.7 to 20 nm with maximums at about 4 nm for OR10J5 and at about 3.65 nm for Olfr16. In addition, by using the two advanced models, the olfactory responses of lyral on OR10J5 and Olfr16 can be used for the energetic characterization of the lyral-OR10J5/Olfr16 binding sites interactions and allowed access to the adsorption energy distributions (AEDs). Then, two approximate olfactory bands can be determined for lyral molecules docked on OR10J5 and Olfr16, which are defined between 3 and 15.5 kJ/mol and between 3.5 and 13.5 kJ/mol, respectively. Lastly, thanks to the proposed models the adsorption entropy of the studied systems can be calculated to describe the disorder and the order on OR10J5 and Olfr16 surfaces (disorder peak of the two olfactory systems was attained when the equilibrium concentration was equal to the concentration at half saturation). Furthermore, the Gibbs free enthalpy and the internal energy were estimated and their negative values indicated that the adsorption phenomenon involved in the olfactory perception was spontaneous and exothermic nature.