The structure of chromophore-grafted amyloid-β(12-28) dimers in the gas-phase: FRET-experiment guided modelling.

We present theoretical modelling, ion mobility spectrometry and action-FRET experiments for chromophore-grafted amyloid-β(12-28) dimers. A first-principles global minimum search based on replica-exchange molecular dynamics (REMD) leads to a compact structure with strong interstrand interactions. We use REMD with a distance restraint that implements an adaptive effective bias upon average FRET-efficiencies and thus guides the sampling by the action-FRET measurement. This procedure leads to a pair of weakly interacting peptides. Ion-mobility confirms that the weakly interacting structure and not the global minimum with strongly interacting peptides is populated in the experiment. The presence of a high energy barrier between the two structural families, as evidenced from the MD data, suggests that a kinetically trapped structure is observed in the experiment.