Purification and Structural Characterization of Aggregation-Prone Human TDP-43 Involved in Neurodegenerative Diseases

Mislocalization, cleavage, and aggregation of the human protein TDP-43 is found in many neurodegenerative diseases. As is the case with many other proteins that are completely or partially structurally disordered, production of full-length recombinant TDP-43 in the quantities necessary for structural characterization has proved difficult. We show that the full-length TDP-43 protein and two truncated N-terminal constructs 1-270 and 1-263 can be heterologously expressed in E. coli. Full-length TDP-43 could be prevented from aggregation during purification using a detergent. Crystals grown from an N-terminal construct (1-270) revealed only the N-terminal domain (residues 1-80) with molecules arranged as parallel spirals with neighboring molecules arranged in head-to-tail fashion. To obtain detergent-free, full-length TDP-43 we mutated all six tryptophan residues to alanine. This provided sufficient soluble protein to collect small-angle X-ray scattering data. Refining relative positions of individual domains and intrinsically disordered regions against this data yielded a model of full-length TDP-43.