H ⁺ Ions and ATP Reshape the Conformational Landscape of an RNA Recognition Motif and Regulate Its Fibrillation

Proteins exist as dynamic ensembles, with their native states comprising interconverting conformational substates critical to their physiological functions and participation in disease states. Fused in sarcoma (FUS), an RNA-binding protein implicated in neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), contains an RNA recognition motif (RRM) known to form fibrillar aggregates. Here, we investigate the conformational plasticity of FUS-RRM in its native state using advanced NMR techniques, particularly ¹⁵N chemical exchange saturation transfer and heteronuclear adiabatic relaxation dispersion experiments, to capture slow and fast microsecond (μs) time scale dynamics. We further examine the influence of environmental factors such as pH and ATP on the conformational plasticity and the aggregation behavior of FUS-RRM. Our findings show that both ATP and pH perturb the fast and slow μs time scale dynamics of FUS-RRM and thus the aggregation behavior. Specifically, a contrasting effect of ATP on slow and fast μs-ms dynamics at pH 6.4 and 4.6, along with the corresponding changes in aggregation behavior, suggests a complex relationship among ATP, pH, and protein aggregation kinetics. The study suggests that these environmental perturbations behave as kinetic regulators of FUS-RRM's propensity for aggregation.