Amyloidogenicity and Cytotoxicity of a Recombinant C-Terminal His(6)-Tagged A beta(1-42)

Aggregation of amyloid beta peptide (A beta) 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 A beta peptides. While the His(6)-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 His(6)-tagged A beta 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 A beta(1-42). Herein, a method to express and purify a mutant C-terminally His(6)-tagged A beta(1-42) (named as A beta(1-42)-His(6)) from Escherichia coli was described. A beta(1-42)-His(6) aggregated into beta-sheet-rich fibrils as shown by thioflavin T fluorescence, atomic force microscopy and circular dichroism spectroscopy. Moreover, the fibrillar recombinant A beta(1-42)-His(6) 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 A beta(1-42). This highlights the biological importance of modification on the molecular structure of A beta. Thus, the easily purified high-quality A beta(1-42)-His(6) offers great advantages for screening aggregation inhibitors or in vitro confirmation of rationally designed drugs for the treatment of AD.