Multivariate effects of pH, salt, and Zn2+ ions on A beta(40) fibrillation

Amyloid-beta (A beta) peptide aggregation plays a central role in the progress of Alzheimer's disease (AD), of which A beta-deposited extracellular amyloid plaques are a major hallmark. The brain micro-environmental variation in AD patients, like local acidification, increased ionic strength, or changed metal ion levels, cooperatively modulates the aggregation of the A beta peptides. Here, we investigate the multivariate effects of varied pH, ionic strength and Zn2+ on A beta(40) fibrillation kinetics. Our results reveal that A beta fibrillation kinetics are strongly affected by pH and ionic strength suggesting the importance of electrostatic interactions in regulating A beta(40) fibrillation. More interestingly, the presence of Zn2+ ions can further alter or even reserve the role of pH and ionic strength on the amyloid fibril kinetics, suggesting the importance of amino acids like Histidine that can interact with Zn2+ ions. Both pH and ionic strength regulate the secondary nucleation processes, however regardless of pH and Zn2+ ions, ionic strength can also modulate the morphology of A beta(40) aggregates. These multivariate effects in bulk solution provide insights into the correlation of pH-, ionic strength- or Zn2+ ions changes with amyloid deposits in AD brain and will deepen our understanding of the molecular pathology in the local brain microenvironment.