Phosphorylation modifies the molecular stability of β-amyloid deposits

Abstract

Protein aggregation plays a crucial role in neurodegenerative diseases. A key feature of protein aggregates is their ubiquitous modification by phosphorylation. Little is known, however, about the molecular consequences of phosphorylation of protein aggregates. Here we show that phosphorylation of β-amyloid at serine 8 increases the stability of its pathogenic aggregates against high-pressure and SDS-induced dissociation. We further demonstrate that phosphorylation results in an elevated number of hydrogen bonds at the N terminus of β-amyloid, the region that is critically regulated by a variety of post-translational modifications. Because of the increased lifetime of phosphorylated β-amyloid aggregates, phosphorylation can promote the spreading of β-amyloid in Alzheimer pathogenesis. Our study suggests that regulation of the molecular stability of protein aggregates by post-translational modifications is a crucial factor for disease progression in the brain.

Phosphorylation Interferes with Maturation of Amyloid-β Fibrillar Structure in the N Terminus

“…In addition, Ser 8 phosphorylation enhances the stability of A␤ aggregates against high pressure-and SDSinduced monomer dissociation (24). Because of a higher compressibility of pS8A␤ aggregates without monomer release, pS8A␤ aggregates undergo a smaller volume decrease upon pressure-assisted monomer dissociation (24). The data reported in the current study demonstrate that phosphorylation at Ser 8 not only influences the stability but also the structure of A␤ aggregates.…”

“…6 and 7). At the same time, this does not exclude the presence of waterexcluded cavities in this region in the structure of npA␤ aggregates, and the lower pressure stability of npA␤ aggregates (24) suggests that indeed this might be the case. In line with this model, the solvent-exposed N-terminal region of pS8A␤ aggregates would contain fewer water-excluded cavities, resulting in a higher resistance of pS8A␤ aggregates against pressure-induced monomer dissociation.…”

“…In addition, Ser 8 phosphorylation enhances the stability of A␤ aggregates against high pressure-and SDSinduced monomer dissociation (24). Because of a higher compressibility of pS8A␤ aggregates without monomer release, pS8A␤ aggregates undergo a smaller volume decrease upon pressure-assisted monomer dissociation (24).…”

“…The fibrils generated by npA␤ and pS8A␤ are similar in morphology, but they show significant differences in the stability against SDS-and pressure-induced dissociation (24). To further investigate the effects of Ser 8 phosphorylation on the properties of A␤ aggregates, 5-day-aggregated A␤ samples were briefly centrifuged (16,000 ϫ g for 30 min), and the pellets and supernatants were examined separately.…”

“…Furthermore, antibodies against the N-terminal region inhibit A␤ amyloid formation (21), and the conformational propensity of the N-terminal region controls the partitioning between A␤ oligomers and protofibrils (22). In addition, phosphorylation at Ser 8 promotes toxic A␤ aggregation both in vitro and in vivo (23) and increases the stability of A␤ aggregates against pressure-and SDS-induced dissociation into monomers (24).…”