Charge substitution shows that repulsive electrostatic interactions impede the oligomerization of Alzheimer amyloid peptides

The strong pH dependence of A beta oligomerization could arise from favorable intermolecular charge-charge interactions between His and carboxylate groups, or, alternatively, by mutual electrostatic repulsion of peptide molecules. To test between these two possibilities, the pH dependence of the oligomerization of A beta and three charge substitution variants with Asp, Glu and His substituted by Ala is measured. All four peptides oligomerize, as detected by thioflavin T fluorescence, turbidity, and amyloid fibril formation; therefore, specific charge-charge interactions are nonessential for oligomerization. The strong negative correlation between net charge and oligomerization indicates that electrostatic repulsion between A beta monomers impedes their association.