In biophysics, the single-particle tracking (SPT) is broadly used to quantify the kinetics of fluorescently-labelled molecules/proteins in live cells. This powerful tool in microscopy permits ones to resolve modes of motion of individual molecules for better understanding their role in such systems. The motion is not limited to pure (Brownian motion) diffusion, but directed, confined, anomalous diffusion are observed too. The study of their effects in live cells is of great interest.
Based on strict analytical calculations and simulations, we show that the confined motion in presence of Brownian motion in complex systems may have two different statistics . One of them has the normal distribution, whereas another, surprisingly, is under the Laplace distribution with fatter tails than the normal case (with thin tails always). Using the experimental data obtained from a recent SPT study on two particle types, G-protein coupled receptors and the G proteins with which the receptors interact, we have detected the normal and Laplace confinements. It is interesting that the contribution of the Laplace confinement is different for G proteins and receptors.
The results are an important step to experimental cell probing and paves the way for a new strategy acting on the processes occurring in live cells through changing the confined motion of molecules into live cells, for example, by drugs. This analytic treatment can be used for different models, thus opening a new direction towards understanding the role of confinement in complex systems.