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Protein aggregation is of particular interest due to its connection with many diseases and disorders. Many factors can alter the dynamics and result of this process, one of them being the diffusivity of the monomers and aggregates in the system. Here, we study experimentally and theoretically an aggregation process in cells, and we identify two distinct physical timescales that set the number and size of aggregates. The first timescale involves fast aggregation of small clusters freely diffusing in the cytoplasm, while, in the second one, the aggregates are larger than the pore size of the cytoplasm and thus barely diffuse, and the aggregation process is slowed down. However, the process is not entirely halted, potentially reflecting a myriad of active but random forces forces that stir the aggregates. Such slow timescale is essential to account for the experimental results of the aggregation process. These results could also have implications in other processes of spatial organization in cell biology, such as phase-separated droplets. SIGNIFICANCE Protein aggregation is a physico-chemical process that underlies many diseases and disorders, such as Alzheimer’s or Huntington’s disease. Here, we study experimental and theoretically the effect of a sharp decrease of diffusivity in the aggregation dynamics, such as the one that could happen in the cell due to the presence of obstacles. We find that two different timescales are important in setting the size of large aggregates and we give an estimate of the size of the aggregate at which this dramatic change in behaviour occurs, which could not be exclusive of protein aggregation but affect many other intracellular processes. |
