POINT SUBSTITUTION IN THE CENTRAL HYDROPHOBIC CLUSTER OF A HUMAN BETA-AMYLOID CONGENER DISRUPTS PEPTIDE FOLDING AND ABOLISHES PLAQUE COMPETENCE

Alzheimer's disease (AD) is pathologically characterized by the presen ce of numerous insoluble amyloid plaques in the brain composed primari ly of a 40-43 amino acid peptide, the human beta-amyloid peptide (A be ta). The process of A beta deposition can be modeled in vitro by depos ition of physiological concentrations of radiolabeled A beta onto pree xisting amyloid in preparations of unfixed AD cerebral cortex. Using t his model system, it has been shown that A beta deposition is biochemi cally distinct from A beta aggregation and occurs readily at physiolog ical A beta concentrations, but which regions and conformations of A b eta are essential to A beta deposition is poorly understood. We report here that an active congener, A beta(10-35)-NH2, displays time depend ence, pH-activity profile, and kinetic order of deposition similar to A beta(1-40), and is sufficiently soluble for NMR spectroscopy in wate r under conditions where it actively deposits. To examine the importan ce of the central hydrophobic cluster of A beta (LVFFA, residues 17-21 ) for in vitro A beta deposition, an A beta(10-35)-NH2 analog with a s ingle point substitution (F19T) in this region was synthesized and exa mined. Unlike A beta(10-35)-NH2, the F19T analog was plaque growth inc ompetent, and NMR analysis indicated that the mutant peptide was signi ficantly less folded than wildtype A beta. These results support previ ous studies suggesting that the plaque competence of A beta correlates with peptide folding. Since compounds that alter A beta folding may r educe amyloid deposition, the central hydrophobic cluster of A beta wi ll be a tempting target for structure-based drug design when high-reso lution structural information becomes available.