Role of the familial Dutch mutation E22Q in the folding and aggregation of the 15–28 fragment of the Alzheimer amyloid-β protein

Abstract

Amyloid fibrils, large ordered aggregates of amyloid ␤ proteins (A␤), are clinical hallmarks of Alzheimer's disease (AD). The aggregation properties of amyloid ␤ proteins can be strongly affected by singlepoint mutations at positions 22 and 23. The Dutch mutation involves a substitution at position 22 (E22Q) and leads to increased deposition rates of the A␤E22Q peptide onto preseeded fibrils. We investigate the effect of the E22Q mutation on two key regions involved in the folding and aggregation of the A␤ peptide through replica exchange molecular dynamics simulations of the 15-28 fragment of the A␤ peptide. The A␤15-28 peptide encompasses the 22-28 region that constitutes the most structured part of the A␤ peptide (the E22-K28 bend), as well as the central hydrophobic cluster (CHC) (segment 17-21), the primary docking site for A␤ monomers depositing onto fibrils. Our simulations show that the 22-28 bend is preserved in the A␤(15-28) peptide and that the CHC, which is mostly unstructured, interacts with this bend region. The E22Q mutation does not affect the structure of the bend but weakens the interactions between the CHC and the bend. This leads to an increased population of ␤-structure in the CHC. Our analysis of the fibril elongation reaction reveals that the CHC adopts a ␤-strand conformation in the transition state ensemble, and that the E22Q mutation increases aggregation rates by lowering the barrier for A␤ monomer deposition onto a fibril. Thermodynamic signatures of this enhanced fibrillization process from our simulations are in good agreement with experimental observations. Alzheimer's disease ͉ explicit water ͉ familial type ͉ molecular dynamics simulations ͉ replica exchange T he presence of amyloid fibrils in the brain is a clinical hallmark of Alzheimer's disease (AD). The fibrils consist of large ordered aggregates of amyloid-␤ (A␤) peptides, proteolytic by-products of the enzymatic cleavage of the Alzheimer amyloid precursor protein (APP). AD can be sporadic (occurring in elderly patients and characterized by a slow progression) or familial (a hereditary form characterized by early onset of the disease and aggravated severity). The majority of familial forms of AD involve single-point mutations in the 22-23 segment of the A␤ peptide. The focus of this work is on the Dutch form of AD, which involves a mutation encoded by a point substitution G to C at codon 693 of the amyloid precursor protein (APP). The result is the production of an A␤ peptide in which residue E22 is mutated to Q (E22Q mutation). Patients who have this mutation are at risk of developing cerebral amyloid angiopathy that typically leads to cerebral hemorrhage and stroke. Many in vitro experiments show that the A␤E22Q peptide aggregates much more readily than its wild-type (WT) counterpart (1-3). As a free monomer in solution, the WT A␤ peptide is for the most part unstructured with residual structure observed locally in a few regions of the primary sequence (4). The A␤ peptide can populate a variety of oligomeric species, some...

A comparative analysis of the aggregation behavior of amyloid‐β peptide variants

“…FAD mutations can thus either inhibit or induce aggregation depending on the suitability of the replacing amino acid to accommodate an amyloidogenic or aggregated structure. Molecular dynamics simulations have suggested the depletion of the E22-K28 salt bridge to explain the enhanced aggregation of E22Q Ab , while the switch of a bend motif to a turn in the region Ab [22][23][24][25][26][27][28] could result in slower aggregation of the D23N Ab 1-42 mutant [25]. Overall fibril morphology is however not affected, as has been shown previously for a subset of FAD mutants [23].…”

“…Alternatively, the denser peptide networks can be more prone to precipitation in the test tube which would lead to a similar observation. Although the effect of FAD-related mutations of Ab 1-42 on aggregation has been investigated in the past [23][24][25][26], no comprehensive study has been reported that directly compares the majority of the currently known mutations. Different Ab preparation methods and experimental conditions have led to considerable variation in reported effects of these mutations.…”

Effects of Familial Alzheimer’s Disease Mutations on the Folding Nucleation of the Amyloid β-Protein

“…30 Our model of the folded Aβ(21-30) fragment satisfies all inter-proton constraints available from our previous NMR study. 9 It also readily explains the origin of the anomalously high hydrogen exchange protection factors observed for residues G25-K28 by Maggio and collaborators in fragments Aβ (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28) and Aβ . 31,32 Our simulations indicate that the amide hydrogens of these residues engage in hydrogen bonds with the side chain of D23 and thus get shielded from water.…”

Crystal Structure of the Amyloid-β p3 Fragment Provides a Model for Oligomer Formation in Alzheimer's Disease

“…The Glu22Gly/Gln/Lys mutations (Fig. 3A) do not directly affect the structure of the 22-28 loop but rather weaken the interactions between this loop and the central hydrophobic segment (amino acids 18 -21), as predicted by molecular dynamic simulations of the A␤ 15-28 Glu22Gln mutant, which increases the propensity of the ␤-structure in the hydrophobic segment (Baumketner et al, 2008).…”