Active droplets controlled by enzymatic reactions

TL;DR

This paper introduces a generic model to study how enzymatic reactions and enzyme dynamics influence the formation, size, and number of protein condensates, providing insights into cellular organization.

Contribution

It presents a novel stochastic model combining enzyme trajectories with protein phase separation, highlighting the role of enzyme concentration and diffusion in condensate regulation.

Findings

Enzyme concentration and diffusion control droplet formation.

Droplet size and number depend on enzyme dynamics.

The model captures stochastic fluctuations affecting condensate behavior.

Abstract

The formation of condensates is now considered as a major organization principle of eukaryotic cells. Several studies have recently shown that the properties of these condensates are affected by enzymatic reactions. We propose here a simple generic model to study the interplay between two enzyme populations and a two-state protein. In one state, the protein forms condensed droplets through attractive interactions, while in the other state, the proteins remain dispersed. Each enzyme catalyzes the production of one of these two protein states only when reactants are in its vicinity. A key feature of our model is the explicit representation of enzyme trajectories, capturing the fluctuations in their local concentrations. The spatially dependent growth rate of droplets naturally arises from the stochastic motion of these explicitly modeled enzymes. Using two complementary numerical methods, (1) Brownian Dynamics simulations, and (2) a hybrid method combining Cahn-Hilliard-Cook diffusion equations with Brownian Dynamics for the enzymes, we investigate how enzyme concentration and dynamics influence the evolution with time, and the steady-state number and size of droplets. Our results show that the concentration and diffusion coefficient of enzymes govern the formation and size-selection of biocondensates.