Controlling β-Amyloid Oligomerization by the Use of Naphthalene Sulfonates

Abstract

Aggregation of proteins and peptides has been shown to be responsible for several diseases known as amyloidoses, which include Alzheimer disease (AD), prion diseases, among several others. AD is a neurodegenerative disorder caused primarily by the aggregation of β-amyloid peptide (Aβ). Here we describe the stabilization of small oligomers of Aβ by the use of sulfonated Hydrophobic molecules such as AMNS (1-amino-5-naphthalene sulfonate); 1,8-ANS (1-anilinonaphthalene-8-sulfonate) and bis-ANS (4,4′-dianilino-1, 1′-binaphthyl-5,5′-disulfonate). The experiments were performed with either Aβ-1-42 or with Aβ-13-23, a shorter version of Aβ that is still able to form amyloid fibrils in vitro and contains amino acid residues 16-20, previously shown to be essential to peptide-peptide interaction and fibril formation. All sulfonated molecules tested were able to prevent Aβ aggregation in a concentration dependent fashion in the following order of efficacy: 1,8-ANS < AMNS < bis-ANS. Size exclusion chromatography revealed that in the presence of bis-ANS, Aβ forms a heterogeneous population of low molecular weight species that proved to be toxic to cell cultures. Since the ANS compounds all have apolar rings and negative charges (sulfonate groups), both hydrophobic and electrostatic interactions may contribute to interpeptide contacts that lead to aggregation. We also performed NMR experiments to investigate the structure of Aβ-13-23 in SDS micelles and found features of an α-helix from Lys16 to Phe20. 1H TOCSY spectra of Aβ-13-23 in the presence of AMNS displayed a chemical-shift dispersion quite similar to that observed in SDS, which suggests that in the presence of AMNS this peptide might adopt a conformation similar to that reported in the presence of SDS. Taken together, our studies provide evidence for the crucial role of small oligomers and their stabilization by sulfonate hydrophobic compounds. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.