Controlling β-amyloid oligomerization by the use of naphthalene sulfonates -: Trapping low molecular weight oligomeric species

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 beta-amyloid peptide (A beta). Here we describe the stabilization of small oligomers of A beta 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'-dianilino1,1'-binaphthyl-5,5'-disulfonate). The experiments were performed with either A beta-1-42 or with A beta-13-23, a shorter version of A beta 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 A beta aggregation in a concentration dependent fashion in the following order of efficacy: 1,8ANS< AMNS< bis-ANS. Size exclusion chromatography revealed that in the presence of bis-ANS, A beta 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 A beta-13-23 in SDSmicelles and found features of an alpha-helix from Lys(16) to Phe(20). H-1 TOCSY spectra of A beta-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.