Comparison of the structural characteristics of Cu(2+)-bound and unbound α-syn12 peptide obtained in simulations using different force fields.

The effects of Cu(2+) binding and the utilization of different force fields when modeling the structural characteristics of α-syn12 peptide were investigated. To this end, we performed extensive temperature replica exchange molecular dynamics (T-REMD) simulations on Cu(2+)-bound and unbound α-syn12 peptide using the GROMOS 43A1, OPLS-AA, and AMBER03 force fields. Each replica was run for 300 ns. The structural characteristics of α-syn12 peptide were studied based on backbone dihedral angle distributions, free-energy surfaces obtained with different reaction coordinates, favored conformations, the formation of different Turn structures, and the solvent exposure of the hydrophobic residues. The findings show that AMBER03 prefers to sample helical structures for the unbound α-syn12 peptide and does not sample any β-hairpin structure for the Cu(2+)-bound α-syn12 peptide. In contrast, the central structure of the major conformational clusters for the Cu(2+)-bound and unbound α-syn12 peptide according to simulations performed using the GROMOS 43A1 and OPLS-AA force fields is a β-hairpin with Turn(9-6). Cu(2+) can also promote the formation of the β-hairpin and increase the solvent exposure of hydrophobic residues, which promotes the aggregation of α-syn12 peptide. This study can help us to understand the mechanisms through which Cu(2+) participates in the fibrillation of α-syn12 peptide at the atomic level, which in turn represents a step towards elucidating the nosogenesis of Parkinson's disease.