Organization of the Proteostasis Network of Membraneless Organelles

Membraneless organelles (MLOs) are dynamic macromolecular condensates that act as crucibles to modulate cellular processes. Since MLOs form in the absence of lipid membranes, it is important to understand how their effective regulation is achieved by the protein homeostasis (proteostasis) system. To address this question, a comprehensive mapping of the proteostasis network (PN) of MLOs, comprising over 220 000 protein-protein interactions is reported. This analysis reveals how regulatory proteins (PN proteins) occupy central roles in the overall protein-protein interaction network of MLOs. It is then investigated which branches of the PN are most important in the regulation of MLOs, finding that the anabolic component, which makes up ≈30% of the PN, is more closely involved than the catabolic component, which makes up the remaining ≈70% of the PN. It is also found that translation-related PN proteins and molecular chaperones play central roles in MLO regulation. Finally, how specificity may be achieved despite shared PN components is explored. These findings suggest that HSP70 chaperones function as generic MLO regulators, while client-specific HSP70 co-chaperones confer specificity to the chaperone action. These results identify the composition of the PN of MLOs, rationalize its organization, and reveal central roles of molecular chaperones in protein regulation within MLOs.