Amyloid β protein

Amyloid β-protein (1-40) that is N-terminally modified with the fluorescent dye (7-diethylaminocoumarin-3-yl)carbonyl (DAC or DEAC). This derivative can be utilized to assess the binding properties of amyloid β-protein (1-40) for various membranes since it behaves very similar to the native peptide. In aqueous environments the fluorophore is almost non-fluorescent whereas binding to membranes results in an increase in fluorescence intensity (Λex = 430 nm, Λem = 470 nm). Increases in the GM1 ganglioside and cholesterol content in the lipid bilayers facilitated the binding of this peptide. For phosphatidylcholine and phosphatidylserine no affinity was observed.

H13R, a mutation in the metal-binding region of Abeta reduces its copper-mediated toxicity. The native rodent sequence containing an arginine at this position is more tolerant to metals than the human amyloid peptide.

The English (H6R) mutation of β-amyloid peptides accelerates fibrillation without increasing protofibril formation. Ono et al. showed that the English and Tottori mutations alter Abeta assembly at its earliest stages, monomer folding and oligomerization, and produce oligomers that are more toxic to cultured neuronal cells than are wild type oligomers. The exchange of His? by Arg influences the structure of the Cu(II) complex formed by Aβ peptides.

The Iowa (D23N) mutant of Aβ 40 considerably more rapidly assembles in solution to form fibrils than the WT Aβ sequence. These fibrils also show a different structure, which could be responsible for their increased toxicity.

SEVNLDAEF corresponds to the mutant junctional sequence of the amyloid precursor protein (APP) found in a Swedish family with early-onset Alzheimer's disease, therefore referred to as the 'Swedish' mutation (K670N/M671L). The peptide has been used for assaying cleavage at leucine-aspartate by cathepsin G and chymotrypsin, whereas neither cathepsin B, D nor L generated any products.

This peptide substrate corresponds to the 'Swedish' Lys-Met/Asn-Leu (K670N/M671L) mutation of the amyloid precursor protein (APP) β-secretase cleavage site. It has been used for assaying β-secretase activity.

Amyloid precursor protein (APP) β-secretase from human brain cleaves full-length APP at the amino terminus of the amyloid β-protein (Aβ) sequence, thus leading to the generation and extracellular release of β-cleaved soluble APP and a corresponding cell-associated carboxy-terminal fragment. The subsequent cleavage of the C-terminal fragment by γ-secretase(s) leads to the formation of Aβ. This new peptide represents a potent substrate analog inhibitor of APP β-secretase with IC?? = 30 nM.

The Tottori (D7N) mutation of β-amyloid peptides accelerates fibrillation without increasing protofibril formation. Ono et al. showed that the English and Tottori mutations alter Abeta assembly at its earliest stages, monomer folding and oligomerization, and produce oligomers that are more toxic to cultured neuronal cells than are wild type oligomers.

The G37D mutant does not show the aggregation behavior of WT Abeta42 nor its neurotoxicity.

Cys-Aβ1-40 can be easily and selectively modified, labeled, coupled to carriers e.g. by maleimide chemistry without affecting the sequences involved in fibril formation. The free mercapto moiety of the peptide adheres to gold surfaces.

Dimer of H-7402.

Aβ40 S26C has been used for generating the covalently linked Aβ40 homodimer. Dimerization can be easily reverted by reducing the soluble dimer with thiols as β-mercaptoethanol. Aβ40 S26C is perfectly suited for labeling with fluorescent tags

The Osaka mutation was the first deletion-type mutation to be identified in APP and Aβ. The Aβ E22delta mutant is more resistant to degradation by two major Aβ-degrading enzymes, neprilysin and insulin-degrading enzyme. Synthetic mutant Aβ showed unusual aggregation properties with enhanced oligomerization but no fibrillization. It also inhibited hippocampal long-term potentiation more efficiently than wild-type Aβ. A transgenic mouse model containing APP with the E693delta mutation has been developed. APP(OSK)-Tg mice exhibit intraneuronal Aβ E22delta oligomers and memory impairment as early as eight months of age.

The Osaka (E22delta) mutation of Amyloid β promotes β-sheet transformation, radical production, and synaptotoxicity, but not neurotoxicity.

The Dutch mutation (E22Q) of amyloid β-peptide aggregates more readily than the wild-type peptide and the resulting fibrils show increased neurotoxicity. The mutant peptide E22Q induced apoptosis of cerebral endothelial cells at a concentration of 25 μm, whereas WT Aβ 1-40 and the Italian mutant E22K (H-6698) showed no effect.

The Dutch mutation (E22Q) aggregates more readily than the wild-type sequence. The resulting fibrils show increased neurotoxicity.

Transgenic mice expressing the vasculotropic Dutch/Iowa (E693Q/D694N) mutant human Aβ precursor protein in brain (Tg-SwDI) accumulate abundant cerebral microvascular fibrillar amyloid deposits and exhibit robust neuroinflammation. In vitro, the doubly mutated Aβ peptides showed an increased propensity to fibrillation and pathogenicity compared to the Dutch and Iowa single mutants.

Contrary to β-amyloid peptides mutated at position 22 (Dutch, Italian, Arctic mutants) the Flemish mutation (A21G) shows a decreased tendency to aggregate and a reduced neurotoxicity. In the studies of Betts and Tsubuki, A21G was degraded significantly more slowly by neprilysin than the wild-type Aβ 1-40 and the E22 mutants. The relative resistance to proteolytic degradation may account for the pathogenicity of the Aβ mutant.

The Flemish mutation (A21G) shows a decreased tendency to aggregate and a reduced neurotoxicity. A21G is pathogenic as it is degraded significantly more slowly by neprilysin than WT Abeta42.

The highly neurotoxic arctic mutant (E22G) of Aβ has been used to study the mechanisms underlying the formation of soluble and insoluble β-amyloid aggregates. As the wild-type Aβ, the arctic mutant preferably assembles in the presence of GM1 ganglioside.

The arctic mutant of amyloid β peptide 1-42, in which Glu²² is substituted by Gly, is distinctly more amyloidogenic than the wild-type Aβ 1-42.