Assembly and aggregation properties of synthetic Alzheimer's A4/beta amyloid peptide analogs (original) (raw)
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Aggregation State and Neurotoxic Properties of Alzheimer Beta-Amyloid Peptide
Neurodegeneration, 1995
THE BETA-AMYLOID PROTEIN (beta-amyloid) is the principle constituent of the senile plaque found in Alzheimer's Disease (AD), representing a 39-43 amino acid fragment of amyloid precursor protein (APP). The factors which initiate the deposition in AD of what is a normal cell product are at present not fully understood. Studies of the effects of beta-amyloid (βA) in vitro have concluded that the peptide may have neurotoxic or neurotrophic effects, depending upon its fibrillar state (Pike et al., 1991, 1993; Yankner et al., 1990a,b) or its presence may increase the vulnerability of the cell to other insults (Mattson et al., 1992). Thus, βA1-42 is neurotrophic in its initially solubilized state but shows aggregation and neurotoxicity in cells in culture after 2-4 day preincubation of the peptide (Pike et al., 1991). Pike and colleagues (1993) later noted, while examining an overlapping series of synthetic βA peptides, that the physical and biological properties differed between peptides of different lengths. In this present report, we show that the fibrillar state and neurotoxic behaviour of βA1-40 varies between synthetic batches of the peptide. Materials and Methods βA1-40 was purchased from Bachem UK Ltd. For the assessment of fibrillization and neurotoxicity, the peptide was dissolved in pure water at 6 mg/ml. Ageing was carried out by incubating this peptide solution at 37°C. Fibrillization was assessed by a method based on that described by Klunk et al. (1989a,b). Briefly, following incubation, peptide was diluted to 400 µg/ml with phosphate buffered saline pH7.4. This solution (25 µl) was then incubated with 225 µl of a Congo red solution (25 µM in 0.1 mM potassium monophosphate and 0.15 M sodium chloride, pH 7.4). After 30 min at room temperature, the fibril amounts were quantified by: CRB(M) ϭ A 540 Ϭ 25 295) Ϫ (A 477 Ϭ 46 306)
European Journal of Biochemistry, 1991
The filamentous amyloid protein aggregates found in the brain of patients affected with Alzheimer's disease principally consist of a peptide termed PA4, according to its secondary structure of P-pleated sheets and its molecular mass of about 4 kDa. It has a length of up to 42 or 43 residues. By chemical means, we have synthesized peptide analogs corresponding to the human and rodent PA4 sequences. We describe structural and functional properties of peptides spanning residues 1-43, 10-23, 1-27 and 4-27 of PA4. The peptides have been tested for their ability to form filaments in vitro. Their solubilities and secondary structures in solution and in the solid state have been used to detect differences between the properties of human and rodent PA4 sequences. We show that mouse and rat PA4 homologs are as amyloidogenic as the human sequence. The absence of amyloid deposits in the brain of aged rats and mice is therefore not due to the three amino acid substitutions identified within the sequence which is homologous to PA4 of humans. Moreover, peptides corresponding to residues 1 -27 of human and rodent PA4 are solubilized under physiological conditions; thus they are very unlikely to form stable filaments in vivo.
Structure of Amyloid A4-(1-40)-Peptide of Alzheimer's Disease
European Journal of Biochemistry, 1995
One of the principal peptide components of the amyloid plaque deposits of Alzheimer's disease in humans is the 40-amino-acid peptide 8-amyloid A4-( 1 -40)-peptide. The full-length A4-( I -40)-peptide was chemically synthesized and the solution structure determined by two-dimensional nuclear magnetic resonance spectroscopy and restrained molecular-dynamics calculations. Synthetic human A4-( 1 -40)peptide was soluble and non-aggregating for several days in 40 % (by vol.) trifluoroethanol/water. All spin systems could be unambiguously assigned, and a total of 203 sequential and medium-range crosspeaks were found in the NOESY (nuclear Overhauser enhancement spectroscopy) spectrum. Long-range NOE cross-peaks that would indicate tertiary structure of the peptide were absent. The main secondarystructure elements found by chemical-shift analysis, sequential and medium-range NOESY data, and NOE-based restrained molecular-dynamics calculations were two helices, Glnl5 -Asp23 and Ile31-Met35, whereas the rest of the peptide was in random-coil conformation. A similar secondary structure is suggested for the aggregation part of prions, the postulated causative agents of the transmissible spongiform encephalopathy. The sequence of the helical part of prion proteins was observed to be remarkably similar to the sequence of the helical part of human A4-(1-40)-peptide.
pH-dependent structural transitions of Alzheimer amyloid peptides
Biophysical Journal, 1991
To understand the molecular interactions leading to the assembly of 1/A4 protein into the hallmark fibrils of Alzheimer's disease (AD), we have examined the ability of synthetic peptides that correspond to the 1/A4 extracellular sequence to form fibrils over the range of pH 3-10. Peptides included the sequences 1
Structural analysis of amyloid ? peptide fragment (25-35) in different microenvironments
Biopolymers, 2004
Amyloid  (A) peptides are one of the classes of amphiphilic molecules that on dissolution in aqueous solvents undergo interesting conformational transitions. These conformational changes are known to be associated with their neuronal toxicity. The mechanism of structural transition involved in the monomeric A to toxic assemblage is yet to be understood at the molecular level. Early results indicate that oriented molecular crowding has a profound effect on their assemblage formation. In this work, we have studied how different microenvironments affect the conformational transitions of one of the active amyloid -peptide fragments (A 25-35). Spectroscopic techniques such as CD and Fourier transform infrared spectroscopy were used. It was observed that a stored peptide concentrates on dissolution in methanol adopts a minor ␣-helical conformation along with unordered structures. On changing the methanol concentration in the solvated film form, the conformation switches to the antiparallel -sheet structure on the hydrophilic surface, whereas the peptide shows transition from a mixture of helix and unordered structure into predominantly a -sheet with minor contribution of helix structure on the hydrophobic surface. Our present investigations indicate that the conformations induced by the different surfaces dictate the gross conformational preference of the peptide concentrate.
Febs Journal, 2006
Beta-amyloid (1–40) (Abeta), the main component of senile plaques seen in the brains of Alzheimer's disease patients, was found to be toxic both as fibrils and smaller soluble globular aggregates. The hydrolytic properties of Abeta, a new biochemical activity described previously [Brzyska M, Bacia A & Elbaum D (2001) Eur J Biochem268, 3443–3454], may contribute to its overall toxicity. In this study, the hydrolysis of fluorescein ester series was studied under predetermined conditions affecting Abeta hydrophobicity and conformation. Reaction products of the most effectively decomposed ester (dibutyrate) were characterized using HPLC and ESI-MS. Hydrophobicity of Abeta, as measured by bis-8-anilinonaphthalene fluorescence, correlated with its hydrolytic abilities. FTIR and CD data analysis showed a relationship between enhanced hydrolytic abilities and Abeta structure. Seriously limited hydrolysis caused by higher peptide concentrations is consistent with monomeric/dimeric Abeta species participation in the process, confirmed by thioflavine T binding. Inhibition of hydrolysis was caused by β-sheet breaker peptide (LPFFD), indicating that the Abeta central hydrophobic cluster (amino acids 17–21) participates in the process. The reported Abeta properties suggest that small conformational alterations of the peptide structure may have a pronounced effect on its functions and biological activity.
Capillary electrophoresis studies on the aggregation process of β‐amyloid 1‐42 and 1‐40 peptides
2004
The possibility to monitor, in solution, the steps of b-amyloid (Ab) nucleation and therefore to describe this dynamic process by using capillary electrophoresis and under optimized experimental conditions is described. Striking differences in the electrophoretic patterns of Ab 1-42 and Ab 1-40 over time are here shown, and different aggregation states are elucidated, which reflect the very diverse oligomerization behavior of two very similar peptides. The isolation of one aggregated species of high molecular weight by ultracentrifugation allowed us to assess its role as toxic oligomer. The perturbation of the existing equilibrium among the identified species by the addition of small molecules can in principle interfere with the aggregation process of the peptides and ultimately prevent the plaque formation in vitro.
Journal of Neuroscience, 2008
Alzheimer's disease is an age-related neurodegenerative disorder with its toxicity linked to the generation of amyloid- peptide (A). Within the A sequence, there is a systemic repeat of a GxxxG motif, which theoretical studies have suggested may be involved in both peptide aggregation and membrane perturbation, processes that have been implicated in A toxicity. We synthesized modified A peptides, substituting glycine for leucine residues within the GxxxG repeat motif (GSL peptides). These GSL peptides undergo -sheet and fibril formation at an increased rate compared with wild-type A. The accelerated rate of amyloid fibril formation resulted in a decrease in the presence of small soluble oligomers such as dimeric and trimeric forms of A in solution, as detected by mass spectrometry. This reduction in the presence of small soluble oligomers resulted in reduced binding to lipid membranes and attenuated toxicity for the GSL peptides. The potential role that dimer and trimer species binding to lipid plays in A toxicity was further highlighted when it was observed that annexin V, a protein that inhibits A toxicity, specifically inhibited A dimers from binding to lipid membranes.