Inhbition of #beta#-Amyloid(40) Fibrillogenesis and Disassembly of #beta#-Amuyloid (40) Fibrils by Short #beta#-Amyloid Congeners Containing N-Methyl Amino Acids at Alternate Residues

摘要

A potential goal in the prevention or therapy of Alzheimer's disease is to decrease or eliminate neuritic plaques composed of fibrillar #beta#-amyloid (A#beta#). In this paper we describe N-methyl amino acid containing congeners of the hydrophobic "core domain" of A#beta# that inhibit the fibrillogenesis of full- length A#beta#. These peptides also disassemble preformed fibrils of full-length A#beta#. A key feature of the inhibitor peptides is that they contain N-methyl amino acids in alternating positions of the sequence. The most potent of these inhibitors, termed A#beta#l6-22m, has the sequence NH2-K(Me-L)V(Me-F)F(Me-A)E- CONH2. In contrast, a peptide, NH2-KL(Me-V)(Me-F)(Me-F)(Me-A)-E-CONH2, with N-methyl amino acids in consecutive order, is not a fibrillogenesis inhibitor. Another peptide containing alternating N-methyl amino acids but based on the sequence of a different fibril-forming protein, the human prion protein, is also not an inhibitor of A#beta#40 fibrillogenesis. The nonmethylated version of the inhibitor peptide, NH2- KLVFFAE-CONH2 (A{316-22), is a weak fibrillogenesis inhibitor. Perhaps contrary to expectations, the A#beta#16-22m peptide is highly soluble in aqueous media, and concentrations in excess of 40 mg/mL can be obtained in buffers of physiological pH and ionic strength, compared to only 2 mg/mL for A#beta#16-22. Analytical ultracentrifugation demonstrates that A#beta#16-22m is monomeric in buffer solution. Whereas A#beta#16-22 is susceptible to cleavage by chymotrypsin, the methylated inhibitor peptide A#beta#16-22m is completely resistant to this protease. Circular dichroic spectroscopy of A#beta#16-22m indicates that this peptide is a #beta#-strand, albeit with an unusual minimum at 226 nm. In summary , the inhibitor motif is that of alternating N-methyl and nonmethylated amino acids in a sequence critical for A{340 fibrillogenesis. These inhibitors appear to act by binding to growth sites of A#beta# nuclei and/or fibrils and preventing the propagation of the network of hydrogen bonds that is essential for the formation of an extended #beta#-sheet fibril.