Dissecting the effect of ALS mutation S375G on the conformational properties and aggregation dynamics of TDP-43 fragment.

The aggregation of transactive response deoxyribonucleic acid (DNA) binding protein of 43 kDa (TDP-43) into ubiquitin-positive inclusions is closely associated with amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration, and chronic traumatic encephalopathy. The 370-375 fragment of TDP-43 (GNNSYS, TDP-43), the amyloidogenic hexapeptides, can be prone to forming pathogenic amyloid fibrils with the characteristic of steric zippers. Previous experiments reported the ALS-associated mutation, serine 375 substituted by glycine (S375G) is linked to early onset disease and protein aggregation of TDP-43. Based on this, it is necessary to explore the underlying molecular mechanisms. By utilizing all-atom molecular dynamics (MD) simulations of 102 μs in total, we investigated the impact of S375G mutation on the conformational ensembles and oligomerization dynamics of TDP-43 peptides. Our replica exchange MD simulations show that S375G mutation could promote the unstructured conformation formation and induce peptides to form a loose packed oligomer, thus inhibiting the aggregation of TDP-43. Further analyses suggest that S375G mutation displays a reduction effect on the number of total hydrogen bonds and contacts among TDP-43 peptides. Hydrogen bonding and polar interactions among TDP-43 peptides, as well as Y374-Y374 π-π stacking interaction, are attenuated by S375G mutation. Additional microsecond MD simulations demonstrate that S375G mutation could prohibit the conformational conversion to β-structure-rich aggregates and possess an inhibitory effect on the oligomerization dynamics of TDP-43. This study offers for the first time of molecular insights into the S375G mutation affecting the aggregation of TDP-43 at the atomic level, and may open new avenues in the development of future site-specific mutation therapeutics.