Evaluation of Copper(II) Transfer between Amyloid-beta Peptides by Relaxation-Induced Dipolar Modulation Enhancement (RIDME)

In the brains of Alzheimer's disease patients, fibrillar aggregates containing amyloid-beta (A beta) peptides are found, along with elevated concentrations of Cu(II) ions. The aggregation pathways of A beta peptides can be modulated by Cu(II) ions and is determined by the formation and nature of the Cu(II)-A beta complex. If spin-labeled, the Cu(II)-A beta complex contains two dipolar coupled paramagnetic centers, the spin label and the Cu(II) ion. Measurement of the dipolar coupling between these paramagnetic centers by relaxation-induced dipolar modulation enhancement (RIDME) allows to monitor the complex formation and thus opens a way to follow the Cu(II) transfer between peptides if a mixture of wild-type and spin-labeled ones is used. We evaluate this approach for a specific Cu(II)-A beta complex, the aggregation-inert Component II. The kinetics of the Cu(II) transfer can be resolved by performing RIDME in a time-dependent manner. A temporal resolution of seconds has been achieved, with the potential to reach milliseconds, using a rapid-freeze quench device to stop the Cu(II) transfer in solution after defined incubation times. Ready, steady, go! Cu(II) ions modulate aggregation of A beta peptides, a hallmark of Alzheimer's disease. Using spin-labeled A beta peptides in combination with relaxation-induced dipolar modulation enhancement and rapid freeze-quench, we introduce a straightforward approach to monitor the transfer of the Cu(II) ions between different A beta peptides. This combined approach paves the way to study dynamic coordination of Cu(II) and understanding its role in the amyloidogenesis of A beta. image