Single-molecule force-spectroscopy reveals aggregation dynamics of intrinsically disordered proteins

Intrisically disordered proteins (IDPs) are flexible biopolymers that lack a fixed, stable structure. Instead, their inherent flexibility expands their interaction radius, thereby increasing the rate and prevalence of molecular interactions. Hence, many IDPs are involved in aggregation-related diseases, such as amyotrophic lateral sclerosis (ALS). Determining the solution conditions and dynamics under which IDP aggregates form is crucial for better understanding these diseases. We use a single-molecule magnetic stretching technique, magnetic tweezers, to measure nanometer-scale structural changes of neurofilament aggregates in real time. We probe single protein chains to determine the interaction energetics and timescales that lead to aggregation. By varying pH and ionic content of the solution, we show that the formation of these aggregates is driven by electrostatic complexation of this polyampholyte. Further, we narrow down the regions responsible for these interactions by probing a truncated version of the protein.