Mechanism of cholesterol-assisted oligomeric channel formation by a short Alzheimer ß-amyloid peptide.

Alzheimer ß-amyloid (Aß) peptides can self-organize into oligomeric ion channels with high neurotoxicity potential. Cholesterol is believed to play a key role in this process, but the molecular mechanisms linking cholesterol and amyloid channel formation have so far remained elusive. Here, we show that the short Aß22-35 peptide, which encompasses the cholesterol-binding domain of Aß, induces a specific increase of Ca(2+) levels in neural cells. This effect is neither observed in calcium-free medium nor in cholesterol-depleted cells, and is inhibited by zinc, a blocker of amyloid channel activity. Double mutations V24G/K28G and N27R/K28R in Aß22-35 modify cholesterol binding and abrogate channel formation. Molecular dynamic simulations suggest that cholesterol induces a tilted α-helical topology of Aß22-35. This facilitates the establishment of an inter-peptide hydrogen bond network involving Asn-27 and Lys-28, a key step in the octamerization of Aß22-35 which proceeds gradually until the formation of a perfect annular channel in a phosphatidylcholine membrane. Overall, these data give mechanistic insights into the role of cholesterol in amyloid channel formation, opening up new therapeutic options for Alzheimer's disease. Aß22-35 peptide, which encompasses the cholesterol binding domain of Aß, induces a specific increase of Ca(2+) level in neural cells. Double mutations V24G/K28G and N27R/K28R modify cholesterol binding and abrogate channels formation. Molecular dynamic simulations suggest that cholesterol induces a tilted α-helical peptide topology facilitating the formation of annular octameric channels, as schematically shown in the graphic (with a hydrogen bond shown in green for two vicinal peptides). Overall, the data give insights into the role of cholesterol in amyloid channel formation and open up new therapeutic options for Alzheimer's disease.

Biochemical identification of a linear cholesterol-binding domain within Alzheimer's ß amyloid peptide.

Alzheimer's ß-amyloid (Aß) peptides can self-organize into amyloid pores that may induce acute neurotoxic effects in brain cells. Membrane cholesterol, which regulates Aß production and oligomerization, plays a key role in this process. Although several data suggested that cholesterol could bind to Aß peptides, the molecular mechanisms underlying cholesterol/Aß interactions are mostly unknown. On the basis of docking studies, we identified the linear fragment 22-35 of Aß as a potential cholesterol-binding domain. This domain consists of an atypical concatenation of polar/apolar amino acid residues that was not previously found in cholesterol-binding motifs. Using the Langmuir film balance technique, we showed that synthetic peptides Aß17-40 and Aß22-35, but not Aß1-16, could efficiently penetrate into cholesterol monolayers. The interaction between Aß22-35 and cholesterol was fully saturable and lipid-specific. Single-point mutations of Val-24 and Lys-28 in Aß22-35 prevented cholesterol binding, whereas mutations at residues 29, 33, and 34 had little to no effect. These data were consistent with the in silico identification of Val-24 and Lys-28 as critical residues for cholesterol binding. We conclude that the linear fragment 22-35 of Aß is a functional cholesterol-binding domain that could promote the insertion of ß-amyloid peptides or amyloid pore formation in cholesterol-rich membrane domains.