A Conformation Change in the Carboxyl Terminus of Alzheimer's Aβ(1–40) Accompanies the Transition from Dimer to Fibril as Revealed by Fluorescence Quenching Analysis

Abstract

Alzheimer's disease is characterized by the presence of insoluble, fibrous deposits composed principally of amyloid ␤ (A␤) peptide. A number of studies have provided information on the fibril structure and on the factors affecting fiber formation, but the details of the fibril structure are not known. We used fluorescence quenching to investigate the solvent accessibility and surface charge of the soluble A␤(1-40) dimer and amyloid fibrils. Analogs of A␤(1-40) containing a single tryptophan were synthesized by substituting residues at positions 4, 10, 34, and 40 with tryptophan. Quenching measurements in the dimeric state indicate that the amino-terminal analogs (A␤F4W and A␤Y10W) are accessible to polar quenchers, and the more carboxyl-terminal analog A␤V34W is less accessible. A␤V40W, on the other hand, exhibits a low degree of quenching, indicating that this residue is highly shielded from the solvent in the dimeric state. Correcting for the effect of reduced translational and rotational diffusion, fibril formation was associated with a selective increase in solvent exposure of residues 34 and 40, suggesting that a conformation change may take place in the carboxyl-terminal region coincident with the dimer to fibril transition.

Structural insights into a yeast prion illuminate nucleation and strain diversity

“…Although it is not yet clear that molten oligomeric species are obligate intermediates in the formation of other amyloids (as it is for NM), they are present in the initial stages of many amyloid assemblies 43,44 . Evidence also attests to the importance of dimeric interactions in the assembly of diverse amyloids [45][46][47] . Recent molecular dynamics simulations with Ab peptide suggest that assembly begins with a molten oligomeric species that allows the rapid sampling of multiple intermolecular contacts, with two individual molecules precipitously finding the right contact and nucleating assembly 44 .…”

Familial Parkinson Disease-associated Mutations Alter the Site-specific Microenvironment and Dynamics of α-Synuclein

“…Therefore, Trp substitution in these positions is not expected to have much effect on the overall hydrophobicity and net charge of the protein. Moreover, substitution of Val with Trp has been previously used effectively to study site-specific conformational changes in A␤ protein (associated with Alzheimer disease) during its aggregation (64). The C-terminal substitution A124W and A140W are also reported not to change the structural properties of ␣-Syn and have been used previously for studying the structural features of ␣-Syn oligomers (59).…”

Structure, Stability, and Aggregation of Paired Helical Filaments from Tau Protein and FTDP-17 Mutants Probed by Tryptophan Scanning Mutagenesis

“…For proteins, such intrinsic signals are essentially restricted to tyrosine and tryptophan residues. Recently some studies (19,20) showed similar approaches for other amyloids. Tau contains 5 Tyr residues but no Trp.…”