Kayed Rakez, Pensalfini Anna, Margol Larry, Sokolov Yuri, Sarsoza Floyd, Head Elizabeth, Hall James, Glabe Charles
Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697, USA.
J Biol Chem. 2009 Feb 13;284(7):4230-7. doi: 10.1074/jbc.M808591200. Epub 2008 Dec 18.
Amyloid oligomers are believed to play causal roles in several types of amyloid-related neurodegenerative diseases. Several different types of amyloid oligomers have been reported that differ in morphology, size, or toxicity, raising the question of the pathological significance and structural relationships between different amyloid oligomers. Annular protofibrils (APFs) have been described in oligomer preparations of many different amyloidogenic proteins and peptides as ring-shaped or pore-like structures. They are interesting because their pore-like morphology is consistent with numerous reports of membrane-permeabilizing activity of amyloid oligomers. Here we report the preparation of relatively homogeneous preparations of APFs and an antiserum selective for APFs (alphaAPF) compared with prefibrillar oligomers (PFOs) and fibrils. PFOs appear to be precursors for APF formation, which form in high yield after exposure to a hydrophobic-hydrophilic interface. Surprisingly, preformed APFs do not permeabilize lipid bilayers, unlike the precursor PFOs. APFs display a conformation-dependent, generic epitope that is distinct from that of PFOs and amyloid fibrils. Incubation of PFOs with phospholipids vesicles results in a loss of PFO immunoreactivity with a corresponding increase in alphaAPF immunoreactivity, suggesting that lipid vesicles catalyze the conversion of PFOs into APFs. The annular anti-protofibril antibody also recognizes heptameric alpha-hemolysin pores, but not monomers, suggesting that the antibody recognizes an epitope that is specific for a beta barrel structural motif.
淀粉样寡聚体被认为在几种与淀粉样相关的神经退行性疾病中起因果作用。已经报道了几种不同类型的淀粉样寡聚体，它们在形态、大小或毒性方面存在差异，这就引发了不同淀粉样寡聚体之间病理意义和结构关系的问题。环形原纤维（APF）在许多不同淀粉样蛋白和肽的寡聚体制剂中被描述为环形或孔状结构。它们很有趣，因为其孔状形态与淀粉样寡聚体膜通透活性的大量报道一致。在这里，我们报告了与前纤维寡聚体（PFO）和纤维相比，相对均一的APF制剂以及对APF具有选择性的抗血清（αAPF）的制备。PFO似乎是APF形成的前体，在暴露于疏水 - 亲水界面后高产率形成。令人惊讶的是，与前体PFO不同，预先形成的APF不会使脂质双层通透。APF显示出一种依赖构象的通用表位，该表位与PFO和淀粉样纤维的表位不同。PFO与磷脂囊泡孵育会导致PFO免疫反应性丧失，同时αAPF免疫反应性相应增加，这表明脂质囊泡催化PFO转化为APF。环形抗原纤维抗体也识别七聚体α - 溶血素孔，但不识别单体，这表明该抗体识别的表位对β桶状结构基序具有特异性。
