Hexanucleotide repeat expansions in C9orf72 are the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD) (c9ALS/FTD). Unconventional translation of these repeats produces dipeptide repeat proteins (DPRs) that may cause neurodegeneration. We performed a modifier screen in Drosophila and discovered a critical role for importins and exportins, Ran-GTP cycle regulators, nuclear pore components and arginine methylases in mediating DPR toxicity. These findings provide evidence for an important role for nucleocytoplasmic transport in the pathogenic mechanism of c9ALS/FTD.

Aggregation is a sequence-specific process, nucleated by short aggregation-prone regions (APRs) that can be exploited to induce aggregation of proteins containing the same APR. Here, we find that most APRs are unique within a proteome, but that a small minority of APRs occur in many proteins. When aggregation is nucleated in bacteria by such frequently occurring APRs, it leads to massive and lethal inclusion body formation containing a large number of proteins. Buildup of bacterial resistance against these peptides is slow. In addition, the approach is effective against drug-resistant clinical isolates ofEscherichiacoliandAcinetobacterbaumannii, reducing bacterial load in a murine bladder infection model. Our results indicate that redundant APRs are weak points of bacterial protein homeostasis and that targeting these may be an attractive antibacterial strategy.

The amyloid-like aggregation propensity present in most globular proteins is generally considered to be a secondary side effect resulting from the requirements of protein stability. Here, we demonstrate, however, that mutations in the globular and amyloid state are thermodynamically correlated rather than simply associated. In addition, we show that the standard genetic code couples this structural correlation into a tight evolutionary relationship. We illustrate the extent of this evolutionary entanglement of amyloid propensity and globular protein stability. Suppressing a 600-Ma-conserved amyloidogenic segment in the p53 core domain fold is structurally feasible but requires 7-bp substitutions to concomitantly introduce two aggregation-suppressing and three stabilizing amino acid mutations. We speculate that, rather than being a corollary of protein evolution, it is equally plausible that positive selection for amyloid structure could have been a driver for the emergence of globular protein structure.

Aggregates of TAR DNA-binding protein (TDP-43) are a hallmark of several neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). Although TDP-43 aggregates are an undisputed pathological species at the end stage of these diseases, the molecular changes underlying the initiation of aggregation are not fully understood. The aim of this study was to investigate how phase separation affects self-aggregation and aggregation seeded by pre-formed aggregates of either the low-complexity domain (LCD) or its short aggregation-promoting regions (APRs). By systematically varying the physicochemical conditions, we observed that liquid–liquid phase separation (LLPS) promotes spontaneous aggregation. However, we noticed less efficient seeded aggregation in phase separating conditions. By analyzing a broad range of conditions using the Hofmeister series of buffers, we confirmed that stabilizing hydrophobic interactions prevail over destabilizing electrostatic forces. RNA affected the cooperativity between LLPS and aggregation in a “reentrant” fashion, having the strongest positive effect at intermediate concentrations. Altogether, we conclude that conditions which favor LLPS enhance the subsequent aggregation of the TDP-43 LCD with complex dependence, but also negatively affect seeding kinetics.