Rapid Assembly of Amyloid- Peptide at a Liquid/Liquid Interface Produces Unstable 
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- 作者：Michael R. Nichols ; Melissa A. Moss ; Dana Kim Reed ; Jan H. Hoh ; and Terrone L. Rosenberry
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：January 11, 2005
- 年：2005
- 卷：44
- 期：1
- 页码：165 - 173
- 全文大小：273K
- 年卷期：v.44,no.1(January 11, 2005)
- ISSN：1520-4995
文摘
Accumulation of aggregated amyloid-
peptide (A) in the brain is a pathological hallmarkof Alzheimer's disease (AD). In vitro studies indicate that the 40- to 42-residue A peptide in solutionwill undergo self-assembly leading to the transient appearance of soluble protofibrils and ultimately toinsoluble fibrils. The A peptide is amphiphilic and accumulates preferentially at a hydrophilic/hydrophobicinterface. Solid surfaces and air-water interfaces have been shown previously to promote A aggregation,but detailed characterization of these aggregates has not been presented. In this study A(1-40) introducedto aqueous buffer in a two-phase system with chloroform aggregated 1-2 orders of magnitude morerapidly than A in the buffer alone. The interface-induced aggregates were released into the aqueousphase and persisted for 24-72 h before settling as a visible precipitate at the interface. Thioflavin Tfluorescence and circular dichroism analyses confirmed that the A aggregates had a -sheet secondarystructure. However, these aggregates were far less stable than A(1-40) protofibrils prepared in bufferalone and disaggregated completely within 3 min on dilution. Atomic force microscopy revealed that theaggregates consisted of small globules 4-5 nm in height and long flexible fibers composed of theseglobules aligned roughly along a longitudinal axis, a morphology distinct from that of A protofibrilsprepared in buffer alone. The relative instability of the fibers was supported by fiber interruptions apparentlyintroduced by brief washing of the AFM grids. To our knowledge, unstable aggregates of A with -sheetstructure and fibrous morphology have not been reported previously. Our results provide the clearestevidence yet that the intrinsic -sheet structure of an in vitro A aggregate depends on the aggregationconditions and is reflected in the stability of the aggregate and the morphology observed by atomic forcemicroscopy. Resolution of these structural differences at the molecular level may provide important cluesto the further understanding of amyloid formation in vivo.
peptide (A) in the brain is a pathological hallmarkof Alzheimer's disease (AD). In vitro studies indicate that the 40- to 42-residue A peptide in solutionwill undergo self-assembly leading to the transient appearance of soluble protofibrils and ultimately toinsoluble fibrils. The A peptide is amphiphilic and accumulates preferentially at a hydrophilic/hydrophobicinterface. Solid surfaces and air-water interfaces have been shown previously to promote A aggregation,but detailed characterization of these aggregates has not been presented. In this study A(1-40) introducedto aqueous buffer in a two-phase system with chloroform aggregated 1-2 orders of magnitude morerapidly than A in the buffer alone. The interface-induced aggregates were released into the aqueousphase and persisted for 24-72 h before settling as a visible precipitate at the interface. Thioflavin Tfluorescence and circular dichroism analyses confirmed that the A aggregates had a -sheet secondarystructure. However, these aggregates were far less stable than A(1-40) protofibrils prepared in bufferalone and disaggregated completely within 3 min on dilution. Atomic force microscopy revealed that theaggregates consisted of small globules 4-5 nm in height and long flexible fibers composed of theseglobules aligned roughly along a longitudinal axis, a morphology distinct from that of A protofibrilsprepared in buffer alone. The relative instability of the fibers was supported by fiber interruptions apparentlyintroduced by brief washing of the AFM grids. To our knowledge, unstable aggregates of A with -sheetstructure and fibrous morphology have not been reported previously. Our results provide the clearestevidence yet that the intrinsic -sheet structure of an in vitro A aggregate depends on the aggregationconditions and is reflected in the stability of the aggregate and the morphology observed by atomic forcemicroscopy. Resolution of these structural differences at the molecular level may provide important cluesto the further understanding of amyloid formation in vivo.