Mechanistic and Structural Characterization of Full‐Length, Aggregation‐Prone, TDP‐43 Protein

Abstract

TAR DNA-binding protein-43 (TDP-43) proteinopathy has been linked to several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) [1]. TDP-43 is a protein that functions in transcriptional repression, the modulation of RNA metabolism, and stress granule formation within cells. As in the case with many other proteins that are partially destructed, characterization of full-length recombinant TDP-43 has proved difficult. This protein is commonly modified post-translationally (PTMs) into aggregated and mutated structures in the cytoplasm and nucleus, including phosphorylation, acetylation, and C-terminal cleavages [2]. Cytoplasmic mislocalization and post-translational modifications of TDP-43 have been linked to aggregate formation, proposedly important for TDP-43-toxicity mechanisms [3, 4]. Since pertinent research has only recently been established on the protein, the pathogenicity and functionality of TDP-43 in ALS has yet to be determined, thus providing us with a critical knowledge gap in TDP-43's functions. Thus, systematic in vitro studies were conducted in our lab to characterize the basic aggregation mechanisms of full-length, native TDP-43 and establish a working model for the in vitro analyses of the protein. Current research on the full-length protein have discovered notable findings regarding the intermolecular properties of TDP-43, providing critical insight into the hydrophobicity of its structure. Along with these intermolecular characteristics and its poor solubility in vitro, the full structure of TDP-43 has not been fully defined. Herein, the in vitro aggregation of TDP-43 protein was achieved and characterized using various spectroscopic methods and electron microscopy. Data indicate that TDP-43 protein is an inherently aggregation-prone protein from the application of several in vitro conditions to induce misfolding of the protein, followed by turbidity and Thioflavin T (ThT) fluorescence assays to monitor β-sheet formation. Transmission electron microscopy (TEM) allowed for visualization of the structural morphologies of these TDP-43 aggregates. As a result, data indicate that full-length TDP-43 protein aggregated under specific environmental conditions and resulted in a high turbidity and ThT intensity. The in vitro analysis of TDP-43 aggregation is a valuable model for future protein studies and provides a preliminary platform for screening therapies towards a viable treatment for ALS.