  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.
