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

Abstract

Neurodegeneration is characterized by the ubiquitous presence of modifications in protein deposits. Despite their potential significance in the initiation and progression of neurodegenerative diseases, the effects of posttranslational modifications on the molecular properties of protein aggregates are largely unknown. Here, we study the Alzheimer disease-related amyloid-␤ (A␤) peptide and investigate how phosphorylation at serine 8 affects the structure of A␤ aggregates. Serine 8 is shown to be located in a region of high conformational flexibility in monomeric A␤, which upon phosphorylation undergoes changes in local conformational dynamics. Using hydrogendeuterium exchange NMR and fluorescence quenching techniques, we demonstrate that A␤ phosphorylation at serine 8 causes structural changes in the N-terminal region of A␤ aggregates in favor of less compact conformations. Structural changes induced by serine 8 phosphorylation can provide a mechanistic link between phosphorylation and other biological events that involve the N-terminal region of A␤ aggregates. Our data therefore support an important role of posttranslational modifications in the structural polymorphism of amyloid aggregates and their modulatory effect on neurodegeneration.

Phosphorylation of a full length amyloid-β peptide modulates its amyloid aggregation, cell binding and neurotoxic properties

“…Our findings reveal that the pAb42 peptide aggregated in a similar manner to its native Ab42 peptide in an aqueous environment, but in the presence of phospholipid POPS/POPC LUVs or POPS/POPC/Chol LUVs, the pAb42 peptide aggregated more rapidly and to a much higher extent compared to the native peptide. These results are in agreement with the pAb40(S8) peptide, which also displayed a similar higher rate and amount of ThT reactive aggregate material compared to the native Ab40 peptide 5,22 while aggregation of pAb40(S26) 23 remained largely unchanged with only a slight increase in ThT absorbance after 30 h of incubation in a lipid-free model experiment. This increased aggregation of pAb42 was confirmed by the CD spectroscopy data, which revealed increased b-sheet formation in the presence of POPS/POPC/Chol LUVs (Fig.…”

“…5 We and others show that pAb is largely in a disordered state. 5,22,23 The combined in vitro data suggest that a lipid environment is an important parameter for the promotion and formation of amyloid structures for the Ab peptide. We have previously shown that Ab peptide binding to neuronal cultures is a key determinant for inducing cell toxicity, with the notable key exception of the D-handed peptide, which while binding to neurons in culture was not toxic.…”

Phosphorylation at Ser8 as an Intrinsic Regulatory Switch to Regulate the Morphologies and Structures of Alzheimer's 40-residue β-Amyloid (Aβ40) Fibrils

“…Phosphorylation Plays Crucial Roles in F p␤ Formation-Recently, Rezaei-Ghaleh et al (46,55) have shown that phosphorylation at Ser 8 could impel the undergoing changes in local conformational dynamics of A␤40, induce the variations of N-terminal exposure of A␤ aggregates, and increase the fibril stability by promoting the formation of strong hydrogen bonds directly. We propose that different conformations of F p␤ fibrils may also be induced directly by phosphorylation.…”

Singlet-filtered NMR spectroscopy

“…The Ab glycines are located within the peptide regions, which are potentially important for the function and/or toxic aggregation of Ab. For example, G9 is preceded by S8, a site of phosphorylation potentially linked to the progression of AD (32,33), and G25 and G29 are close to S26 whose phosphorylation interferes with the Ab fibrillar aggregation (34). It has also been suggested that G37 and G38 are involved in the turn formation in the C-terminal region, where its stabilization in the C-terminally extended Ab42 variant probably plays a role in the higher propensity of Ab42 to toxic aggregation (35).…”