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The Binding Time for an Olfactory Receptor and Its Ligand

In our experimental design, we add heptanal on the papers which have the immobilized mOR103-15 and fluorescent protein (control group), and we put the papers in the water for a few second to wash off the unbinding heptanal. Hence, it is important for us to know how long will it take for mOR103-15 to bind to heptanal and for the binding complex separating from each other, so that we can know when to put the papers in the water is most appropriate.


We refer to the kinetic model proposed by Karl-Ernst Kaissling in 19981. In the model, Kaissling investigated the interaction between pheromone and the receptor on the moth Antheraea Polyphemus with dose-and-response curve, and used receptor potential amplitudes gotten from experiments to estimate, deduce, and calculate the parameters in his model.

Fig 1. The schematic diagram of the model. R is the receptor. S is the reduced form of pheromone, which can bind to the receptor to form the complex RS, which can elicit cell excitation. P is the oxidized/deactivated form of pheromone, which cannot bind to the receptor.
Source: Kaissling, K.-E. Pheromone Deactivation Catalyzed by Receptor Molecules: a Quantitative Kinetic Model. Chemical Senses 23, 385-395, doi:10.1093/chemse/23.4.385 (1998).
Fig 2. The concentration versus time graph drawn by computer model after inputting each parameters. From 0 to 5s, the receptor has stimulus uptake rate U = 1uM/s. (The uptake rate is defined as the number of pheromone molecule which is adsorbed per second by a sensory hair of the moth, and divide the number by 2.6pl—the volume of a hair.) After 5s, the concentration of both S and RS declined exponentially, and the half life of RS is 0.79s.
Source: Kaissling, K.-E. Pheromone Deactivation Catalyzed by Receptor Molecules: a Quantitative Kinetic Model. Chemical Senses 23, 385-395, doi:10.1093/chemse/23.4.385 (1998).

From the above model, we found that the half life of RS is quite short. If the half life of the mOR103-15-heptanal binding complex is as short as this one, it will be rather difficult for us to perform the experiment. However, “the uptake rate” gave us an inspiration—if the concentration of heptanal is far bigger than that of mOR103-15, the existing time of mOR103-15-heptanal binding complex can be “extended”. That is, a single mOR103-15 molecule have to bind with lots of heptanal molecule one after another. Though the half life of an mOR103-15-heptanal binding complex may be short, it can exist for a longer time macroscopically.

Fig 3. The schematic diagram of our idea of extend the existing time of mOR103-15-heptanal binding complex.

References

  1. Kaissling, K.-E. Pheromone Deactivation Catalyzed by Receptor Molecules: a Quantitative Kinetic Model. Chemical Senses 23, 385-395, doi:10.1093/chemse/23.4.385 (1998).
  2. Abaffy, T. The molecular basis for ligand specificity in a mouse olfactory receptor: a network of functionally important residues. Journal of Biological Chemistry 12, 282(2):1216-24 (2007).