Gordon D J, Sciarretta K L, Meredith S C
Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
Biochemistry. 2001 Jul 27;40(28):8237-45. doi: 10.1021/bi002416v.
A potential goal in the prevention or therapy of Alzheimer's disease is to decrease or eliminate neuritic plaques composed of fibrillar beta-amyloid (Abeta). In this paper we describe N-methyl amino acid containing congeners of the hydrophobic "core domain" of Abeta that inhibit the fibrillogenesis of full-length Abeta. These peptides also disassemble preformed fibrils of full-length Abeta. 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 Abeta16-22m, has the sequence NH(2)-K(Me-L)V(Me-F)F(Me-A)E-CONH(2). In contrast, a peptide, NH(2)-KL(Me-V)(Me-F)(Me-F)(Me-A)-E-CONH(2), 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 Abeta40 fibrillogenesis. The nonmethylated version of the inhibitor peptide, NH(2)-KLVFFAE-CONH(2) (Abeta16-22), is a weak fibrillogenesis inhibitor. Perhaps contrary to expectations, the Abeta16-22m 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 Abeta16-22. Analytical ultracentrifugation demonstrates that Abeta16-22m is monomeric in buffer solution. Whereas Abeta16-22 is susceptible to cleavage by chymotrypsin, the methylated inhibitor peptide Abeta16-22m is completely resistant to this protease. Circular dichroic spectroscopy of Abeta16-22m 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 Abeta40 fibrillogenesis. These inhibitors appear to act by binding to growth sites of Abeta 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.
阿尔茨海默病预防或治疗的一个潜在目标是减少或消除由纤维状β-淀粉样蛋白（Aβ）组成的神经炎性斑块。在本文中，我们描述了Aβ疏水“核心结构域”中含N-甲基氨基酸的同系物，它们可抑制全长Aβ的纤维形成。这些肽还能拆解全长Aβ预先形成的纤维。抑制肽的一个关键特征是它们在序列的交替位置含有N-甲基氨基酸。其中最有效的抑制剂称为Aβ16 - 22m，其序列为NH(2)-K(Me-L)V(Me-F)F(Me-A)E-CONH(2)。相比之下，一种肽NH(2)-KL(Me-V)(Me-F)(Me-F)(Me-A)-E-CONH(2)，其N-甲基氨基酸是连续排列的，不是纤维形成抑制剂。另一种含有交替N-甲基氨基酸但基于不同纤维形成蛋白（人类朊蛋白）序列的肽，也不是Aβ40纤维形成的抑制剂。抑制剂肽的非甲基化版本NH(2)-KLVFFAE-CONH(2)（Aβ16 - 22）是一种弱纤维形成抑制剂。也许与预期相反，Aβ16 - 22m肽在水性介质中高度可溶，在生理pH和离子强度的缓冲液中可获得超过40 mg/mL的浓度，而Aβ16 - 22仅为2 mg/mL。分析超速离心表明Aβ16 - 22m在缓冲溶液中是单体。虽然Aβ16 - 22易被胰凝乳蛋白酶切割，但甲基化的抑制剂肽Aβ16 - 22m对这种蛋白酶完全抗性。Aβ16 - 22m的圆二色光谱表明该肽是β-链，尽管在226 nm处有一个不寻常的最小值。总之，抑制剂基序是在对Aβ40纤维形成至关重要的序列中交替出现N-甲基和非甲基化氨基酸。这些抑制剂似乎通过与Aβ核和/或纤维的生长位点结合并阻止对延伸β-折叠纤维形成至关重要的氢键网络的传播来发挥作用。
