Molecular Insight into Cu2+-Induced Conformational Transitions of Amyloid β-Protein from Fast Kinetic Analysis and Molecular Dynamics Simulations

Cu2+-mediated amyloid beta-protein (A beta) aggregation is implicated in the pathogenesis of Alzheimer's disease, so it is of significance to understand Cu2+-mediated conformational transitions of A beta. Herein, four A beta mutants were created by using the environment-sensitive cyanophenylalanine to respectively substitute F4, Y10, F19, and F20 residues of A beta(40). By using stopped-flow fluorescence spectroscopy and molecular dynamics (MD) simulations, the early stage conformational transitions of the mutants mediated by Cu2+ binding were investigated. The fast kinetics unveils that Cu2+ has more significant influence on the conformational changes of N-terminal (F4 and Y10) than on the central hydrophobic core (CHC, F19, and F20) under different pH conditions (pH 6.6-8.0), especially Y10. Interestingly, lag periods of the conformational transitions are observed for the F19 and F20 mutants at pH 8.0, indicating the slow response of the two mutation sites on the conformational transitions. More importantly, significantly longer lag periods for F20 than for F19 indicate the conduction of the transition from F19 to F20. The conduction time (difference in lag period) decreases from 4.5 s at Cu2+ = 0 to undetectable (<1 ms) at Cu2+ = 10 mu M. The significant difference in the response time of F19 and F20 and the fast local conformational changes of Y10 imply that the conformational transitions of A beta start around Y10. MD simulations support the observation of hydrophobicity increase at N-terminal during the conformational transitions of AP-Cu2+. It also reveals that Y10 is immediately approached by Cu2+, supporting the speculation that the starting point of conformational transitions of is near Y10. The work has provided molecular insight into the early stage conformational transitions of A beta 40 mediated by Cu2+.

Automated summary

This study investigates the early stage conformational transitions of A beta 40 mediated by Cu2+ through the use of mutant variants. Results show that Cu2+ has a significant impact on the conformational changes of the N-terminal residues (F4 and Y10) compared to the central hydrophobic core residues (F19 and F20). The observation of lag periods for F19 and F20 mutants at pH 8.0 suggests a slower response at these mutation sites in the conformational transitions.