Redox-mediated regulation of a labile, evolutionarily conserved cross-β structure formed by the TDP43 low complexity domain

An evolutionarily conserved low complexity (LC) domain is found within a 152 residue segment localized to the carboxyl-terminal region of the TDP43 RNA-binding protein. This TDP43 LC domain contains ten conserved methionine residues. Self-association of this domain leads to the formation of liquid-like droplets composed of labile, cross-{beta} polymers. Exposure of polymers to low concentrations of H2O2 leads to a phenomenon of droplet melting that can be reversed upon exposure of the oxidized protein to the MsrA and MsrB methionine sulfoxide reductase enzymes, thioredoxin, thioredoxin reductase and NADPH. Morphological features of the cross-{beta} polymers were revealed by a method of H2O2-mediated footprinting. Similar TDP43 LC domain footprints were observed in highly polymerized, hydrogel samples, liquid-like droplet samples, and living cells. The ability of H2O2 to impede cross-{beta} polymerization was abrogated by a prominent ALS-causing mutation that changes methionine residue 337 to valine. These observations offer potentially useful insight into the biological role of TDP43 in facilitating synapse-localized translation, as well as aberrant aggregation of the protein in neurodegenerative disease.