Structural and Mechanistic Heterogeneity of the Phase Separation and Aggregation of Full-Length TDP-43 is Governed by Environmental Conditions

TAR DNA-binding protein 43 (TDP-43) is an essential physiological protein implicated in several fatal neurodegenerative disorders. Interestingly, the nature of TDP-43 aggregates varies across patients and disease conditions, suggesting an underlying heterogeneity in its self-assembly behavior. In this study, we investigated two native-like states of full-length TDP-43: the native dimer (N form) and the native-like oligomer (O form). These are compact, folded states with similar secondary structures but differ in size. We found that the N and O forms respond differently to external perturbations and form distinct self-assemblies under stress conditions. Under electrostatic stress, both N and O forms undergo phase separation but produce condensates with markedly different morphologies and dynamics. The underlying mechanisms driving their phase separation are different. Under thermal stress, both forms convert into amyloid aggregates, but again with clearly different morphologies, biochemical properties, and aggregation pathways. These results demonstrate that multiple conformations of TDP-43 respond to distinct perturbations by assembling into structurally and mechanistically different higher-order assemblies. Our findings highlight how the interplay among the structural state, solvation environment, and self-assembly mechanism governs the heterogeneity of TDP-43 assemblies, offering new insights into their physiological roles and pathological relevance. This study suggests that the heterogeneity observed in patients associated with TDP-43 aggregation may arise from differences in the cellular stresses experienced by the protein and the corresponding assembly mechanisms engaged.