Amyloidogenicity and Cytotoxicity of a Recombinant C-Terminal His₆-Tagged Aβ_1-42

Aggregation of amyloid β peptide (Aβ) is closely associated with the occurrence and development of Alzheimer's disease (AD). Reproducible and detailed studies on the aggregation kinetics and structure of various aggregates have been conducted using recombinant Aβ peptides. While the His₆-tag is commonly used in the purification of recombinant proteins due to its great simplicity and affinity, there is little information on the aggregation of His₆-tagged Aβ and its corresponding cytotoxicity. Moreover, it is also unclear whether there is an effect of the His₆-tag on the amyloidogenicity and cytotoxicity of recombinant Aβ_1-42. Herein, a method to express and purify a mutant C-terminally His₆-tagged Aβ_1-42 (named as Aβ_1-42-His₆) from Escherichia coli was described. Aβ_1-42-His₆ aggregated into β-sheet-rich fibrils as shown by thioflavin T fluorescence, atomic force microscopy and circular dichroism spectroscopy. Moreover, the fibrillar recombinant Aβ_1-42-His₆ showed strong toxicity toward PC12 cells in vitro. Molecular dynamics simulations revealed that the His₆-tag contributed little to the secondary structure and intermolecular interactions, including hydrophobic interactions, salt bridges, and hydrogen bonding of the fibrillar pentamer of Aβ_1-42. This highlights the biological importance of modification on the molecular structure of Aβ. Thus, the easily purified high-quality Aβ_1-42-His₆ offers great advantages for screening aggregation inhibitors or in vitro confirmation of rationally designed drugs for the treatment of AD.