The Hitchhiker model for Laplace diffusion processes in the cell environment

TL;DR

This paper introduces the Hitchhiker model to explain how aggregation and fragmentation in cellular environments lead to non-Brownian diffusion behaviors, such as Laplace distributions, by considering size fluctuations of molecules.

Contribution

The Hitchhiker model provides a microscopic explanation for the emergence of Laplace diffusion and diffusivity modulations in intracellular transport.

Findings

Laplace distributions are reproduced in simulations tracking single or multiple molecules.

Diffusivity varies with tracking protocol and size fluctuations.

Single molecule diffusivity is generally lower than ensemble average.

Abstract

Aggregation and fragmentation of single molecules in the cell environment lead to a spectrum of diffusivities and to statistical laws of movement very different from typical Brownian motion. Current models of intracellular transport do not explain at a microscopical level the emergence of theses deviations. Employing a many body approach, which we call the Hitchhiker model, we elucidate how the widely observed exponential tails in the particle spreading, i.e. the Laplace distribution and the modulations of the diffusivities, are controlled by size fluctuations of single molecules. By means of numerical simulations Laplace distributions are obtained whether we track one molecule or many molecules in parallel. However, we show that the diffusivity varies significantly depending on which tracking protocol is applied. Using a renewal process in the space of sizes, we quantify to what extent the average diffusivity in the single molecule technique is decreased compared with the ensemble average.