Structure determination of extracellular fragments of amyloid proteins involved in Alzheimer's disease and Dutch‐type hereditary cerebral haemorrhage with amyloidosis

Abstract

Amyloid deposition is a biochemical and histopathologic hallmark of various clinical forms of amyloidoses including Alzheimer's disease and the Dutch‐type hereditary cerebral haemorrhage with amyloidosis. The self‐aggregating peptides responsible for these irreversible deposits have been sequenced but the mechanisms involved in the aggregation processes are not well understood. In order to gain an understanding of the possible structures prior to self‐association, the extracellular fragment of the Alzheimer amyloid protein (βA4) responsible for the deposits (the ‘native’ fragment) and a mutant of this with a single residue substitution (which is responsible for deposits in the Dutch‐type amyloidosis) were examined by 1H‐NMR spectroscopy. Interproton distance constraints were derived from NMR experimental data and incorporated into tertiary structure calculations using a simulated annealing protocol. Solution conformations of the fragment peptides associated with the two forms of amyloidoses are presented and compared. Although in both peptides the existence of a mixture of conformations in equilibrium is likely, one such population of structures possesses a flexible N‐terminus and a well defined C‐terminal region. The latter region includes a helical segment and a terminal turn‐like structure. These structural features may be important for the basis of amyloid formation. Comparison of the calculated structures of the two peptides revealed a conformationally different region arising from the conservative substitution of Gln22 for Glu22. This region may be responsible for altered binding in the mutant peptide, giving rise to the clinically different form of amyloidosis.

Alzheimer's Aβ40 Studied by NMR at Low pH Reveals That Sodium 4,4-Dimethyl-4-silapentane-1-sulfonate (DSS) Binds and Promotes β-Ball Oligomerization

“…2B). NOEs were also observed between the aromatic side chains of Phe 19 and Phe 20 with the alkyl side chains of Val 18 , Ala 21 , and Val 24 ( Fig. 2C), indicating that these apolar side chains lie close together and form a hydrophobic cluster, which is at least partially populated.…”

“…7) These two regions have a slight tendency to adopt extended backbone structures at pH 2.5 and 25°C as revealed by the conformational shifts and backbone NOE intensities in monomeric A␤. 8) A turn, residues 22-25, stabilized by a small hydrophobic cluster involving Val 24 , Ala 21 , Phe 20 , Phe 19 , and Val 18 , detected by NOEs in monomeric A␤, may form between these two hydrophobic regions. It should be borne in mind that the NMR data reported here correspond to the A␤ monomer.…”

“…9) ␤-Balls, as resolved by atomic force microscopy, appear spherical and have a diameter that ranges from 8 to 18 nm with a mean of 15 nm (11). 10) The trimethylsilyl and first methylene moieties of DSS bound specifically to the aromatic rings of Phe 19 and Phe 20 and to additional alkyl side chain(s), which most likely belong to the central or Cterminal hydrophobic regions. 11) DSS was found to promote the oligomerization of A␤40 and cause the number of A␤40 monomers in the ␤-balls to double.…”

“…This obstacle was first surmounted by the pioneering studies of Zagorski and co-workers, who used cosolvents (18) and detergents (19) to solubilize monomeric A␤. NMR studies of monomeric A␤ in organic solvents (20), in cosolvents (18,21), or associated with detergent micelles (19,(22)(23)(24) revealed extensive helix formation. In contrast, no helical structure was detected in water without cosolvents when more soluble fragments of A␤ peptides and large sample volumes in a 10-mm NMR probe were used to overcome low solubility (25).…”

Cerebral amyloidosis, amyloid angiopathy, and their relationship to stroke and dementia

“…Although the mechanism of fibril formation is not known, in vitro studies [3,5,62] have shown that the Aβ-Q22 variant forms fibrils at a more accelerated rate than wild-type Aβ. This increased amyloidogenic tendency is probably due to a higher content of β-pleated sheet structure and a conformational change in the middle part of the molecule induced by the disappearance of the negatively charged Glu side-chain in the mutant peptide [9,45]. The presence of both allele products in the amyloid deposits suggest that the mutant peptide may induce a conformational change in the structure of the normal Aβ peptide.…”