Guardians of Disorder
Guardians of Disorder
Intrinsically disordered proteins (IDPs) play key roles in cellular organization through their ability to undergo phase separation, yet their aggregation propensity poses a challenge for protein quality control (PQC). The nuclear pore complex (NPC), which regulates the selective transport between the nucleus and cytoplasm, exemplifies this challenge. Its permeability barrier consists of intrinsically disordered phenylalanine–glycine nucleoporins (FG-Nups) that must remain dynamic and functional. Because FG-Nups share biophysical properties with disease-associated IDPs, similar PQC mechanisms likely regulate both physiological and pathological phase behavior. Here, we investigated how molecular chaperones regulate FG-Nups.
Based on biochemical and cell-based assays we demonstrate that the chaperone DNAJB6 directly interacts with FG-Nups, maintains their solubility, and suppresses aggregation in vitro and in cells. This chaperone function is important for NPC assembly during interphase.
We further developed PhaseMetrics, a semi-automated analysis tool to quantify condensate properties in microscopy images. It reliably detects changes in FG-Nup condensates and reveals variability within condensate populations and subtle differences at the level of individual condensates.
Finally, we show that multiple J-domain proteins, including DNAJB6, interact with multiple FG-Nups and delay their aggregation. In DNAJB6, this activity is encoded within a highly conserved intrinsically disordered domain. DNAJB6 forms gel-like structures and we propose that in these chaperone condensates stable homotypic FG-Nup interactions are prevented and dynamic, multivalent heterotypic chaperone:FG-Nup interactions are promoted, preventing unwanted FG-Nup phase transitions.
Together, these findings in this thesis of Tessa Bergsma demonstrate that molecular chaperones not only support protein folding but also regulate physiological phase behavior, safeguarding IDP integrity and NPC function.