Zinc as chaperone-mimicking agent for retardation of amyloid β peptide fibril formation

Abstract

Metal ions have emerged to play a key role in the aggregation process of amyloid β (Aβ) peptide that is closely related to the pathogenesis of Alzheimer's disease. A detailed understanding of the underlying mechanistic process of peptide-metal interactions, however, has been challenging to obtain. By applying a combination of NMR relaxation dispersion and fluorescence kinetics methods we have investigated quantitatively the thermodynamic Aβ-Zn 2+ binding features as well as how Zn 2+ modulates the nucleation mechanism of the aggregation process. Our results show that, under near-physiological conditions, substoichiometric amounts of Zn 2+ effectively retard the generation of amyloid fibrils. A global kinetic profile analysis reveals that in the absence of zinc Aβ 40 aggregation is driven by a monomer-dependent secondary nucleation process in addition to fibril-end elongation. In the presence of Zn 2+ , the elongation rate is reduced, resulting in reduction of the aggregation rate, but not a complete inhibition of amyloid formation. We show that Zn 2+ transiently binds to residues in the N terminus of the monomeric peptide. A thermodynamic analysis supports a model where the N terminus is folded around the Zn 2+ ion, forming a marginally stable, short-lived folded Aβ 40 species. This conformation is highly dynamic and only a few percent of the peptide molecules adopt this structure at any given time point. Our findings suggest that the folded Aβ 40 -Zn 2+ complex modulates the fibril ends, where elongation takes place, which efficiently retards fibril formation. In this conceptual framework we propose that zinc adopts the role of a minimal antiaggregation chaperone for Aβ 40 .Alzheimer's disease | amyloid beta peptide | aggregation kinetics | zinc ion interactions | NMR relaxation

The Rapid Exchange of Zinc2+ Enables Trace Levels to Profoundly Influence Amyloid-β Misfolding and Dominates Assembly Outcomes in Cu2+/Zn2+ Mixtures

“…Interestingly, an increase in lag-times were observed with addition of Zn 2+ , but no reduction in ThT intensity was reported [43]. We wondered if this conflict with our own data, shown in figure 3, might be due to the use of phosphate buffer, which will compete for Zn 2+ and form poorly soluble ZnPO 4 .…”

“…Recently a study reported the effect of Zn 2+ on Aβ fibre formation, using ThT to monitor fibre formation kinetics [43]. Interestingly, an increase in lag-times were observed with addition of Zn 2+ , but no reduction in ThT intensity was reported [43].…”

“…Zn 2+ is thought to induce Aβ to rapidly form disc shaped oligomers that are highly toxic to primary cell culture, but may then further aggregate to form non-toxic assemblies [42]. Conversely, it was recently reported that Zn 2+ can slow Aβ fibre growth, without affecting the number of fibres ultimately formed [43]. Consequently, though many studies agree that Zn 2+ has a profound effect on Aβ misfolding, which aggregate species develop from the Aβ-Zn 2+ interaction is still not fully resolved.…”

Preventing peptide and protein misbehavior

“…1. In PNAS, Abelein et al (7) prove that the microscopic mechanism is not perturbed by zinc, and is still dominated by the same processes observed in the absence of the metal ion. The presence of zinc does, however, delay the aggregation process by inhibiting significantly and exclusively only the elongation of fibrils by monomer.…”

“…The work of Abelein et al (7) is a remarkable demonstration of how advances in the understanding of a complex aggregation reaction mechanism can be achieved by a combination of chemical kinetic analysis and experimental characterization, and how the molecular effects that alter interactions between individual peptides and proteins can be translated into observable differences in the macroscopic behavior. Even though the species involved in this study, zinc ions, are unlikely to form the basis for a therapeutic strategy as such, the power of the approach demonstrated by Abelein et al (7) for controlling protein aggregation raises the hope that, in the future, this strategy will pave the way to a rational design of potent inhibitors of aggregation.…”