Inhibitory Effect of Choline- O-sulfate on Aβ_16-22 Peptide Aggregation: A Molecular Dynamics Simulation Study

The aggregation of Aβ_16-22 peptide, the smallest fragment of full-length Aβ_1-42 with seven residues, plays a very crucial role in Aβ toxicity, hence causing Alzheimer's disease. Alzheimer's disease (AD) is a progressive neurodegenerative disease associated with brain disorder, and currently there is no treatment available in the market to cure it permanently. So, drug design for the curable treatment of AD is a very challenging problem. In this study, we have investigated the inhibitory effect of choline- O-sulfate (COS) in the oligomerization of Aβ_16-22 peptide. We have carried out a series of classical simulations using two different types of force field parameters, namely, CGenFF and GAFF and found that this small seven residue peptide aggregates in pure water to form fibrils but in the presence of the inhibitor COS, the formation of β-sheet structure is prevented. Residue-wise secondary structure analysis shows that the hydrophobic core of the peptide LVFFA contains high percentage of ordered β-sheet conformation in pure water which becomes negligible with the addition of COS. Different types of interaction energies, radial distribution functions, coordination number calculation, and hydrogen bond analysis show that COS interacts with the peptide backbone nitrogen through hydrogen bonding as well as the solvation of peptide hydrophobic residues by it, playing a major role to prevent the peptide aggregation in water. It is worth mentioning that the results obtained from both of the force field parameters draw very similar conclusions. In this work, we have also shown that COS can disaggregate the preformed five-stranded protofibril of Aβ_16-22 at a concentration of 0.95 M.