Structural Characterization of a Soluble Amyloid β-Peptide Oligomer
ABSTRACT Alzheimer's disease (AD) is a neurodegenerative disorder that is linked to the presence of amyloid beta-peptides that can form insoluble fibrils or soluble oligomeric assemblies. Soluble forms are present in the brains and tissues of Alzheimer's patients, and their presence correlates with disease progression. Long-lived soluble forms can be generated in vitro by using small amounts of aliphatic hydrocarbon chains of detergents or fatty acids in preparations of amyloid beta-peptides. Using NMR, we have characterized soluble oligomers of Abeta preglobulomer and globulomer that are stable and alter synaptic activity. The NMR data indicate that these soluble forms have a mixed parallel and antiparallel beta-sheet structure that is different from fibrils which contain only parallel beta-sheets. Using the structural data, we engineered a disulfide bond into the soluble Abeta globulomer to give a "new" soluble antigen that is stable, homogeneous, and binds with the same affinity to selective antibodies as the parent wt globulomer.
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ABSTRACT: Abnormal protein folding and self-assembly causes over 30 cureless human diseases for which no disease-modifying therapies are available. The common side to all these diseases is formation of aberrant toxic protein oligomers and amyloid fibrils. Both types of assemblies are drug targets, yet each presents major challenges to drug design, discovery, and development. In this review, we focus on two small molecules that inhibit formation of toxic amyloid protein assemblies - the green-tea derivative (-)-epigallocatechin-3-gallate (EGCG), which was identified through a combination of epidemiologic data and a compound library screen, and the molecular tweezer CLR01, whose inhibitory activity was discovered in our group based on rational reasoning, and subsequently confirmed experimentally. Both compounds act in a manner that is not specific to one particular protein and thus are useful against a multitude of amyloidogenic proteins, yet they act via distinct putative mechanisms. CLR01 disrupts protein aggregation through specific binding to lysine residues, whereas the mechanisms underlying the activity of EGCG are only recently beginning to unveil. We discuss current in vitro and, where available, in vivo literature related to EGCG and CLR01's effects on amyloid beta-protein, alpha-synuclein, transthyretin, islet amyloid polypeptide, and calcitonin. We also describe the toxicity, pharmacokinetics, and mechanism of action of each compound.12/2013; 4(4-4):385-409. DOI:10.2478/s13380-013-0137-y
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ABSTRACT: Oxidative stress and amyloid-β (Aβ) formation are important processes that occur in Alzheimer's disease (AD). Amyloid formation is associated with the aggregation and precipitation of the Aβ peptide, while oxidative stress results from an imbalance in pro-oxidant/antioxidant homeostasis that produces harmful reactive oxygen species. The methionine-35 (Met35) residue of the Aβ peptide plays an important role in AD oxidative stress events and the associated neurotoxicity. We and other research groups previously demonstrated that in vitro oxidation of the Met35 side-chain to the sulfoxide (Met35red → Met35ox) impedes assembly and aggregation of monomeric Aβ peptide into protofibrils, the latter being the immediate precursors of amyloid plaques. Here, we report that Met35 oxidation state affects the stability of preexisting amyloid fibrils and plaques, where the Met35red → Met35ox process leads to changes in the morphology of filaments, protofibrils, mature fibrils, and loss of Congo red birefringence in senile plaques isolated from the brains of AD patients. The most notable differences were in fibril flexibility, as evidenced by changes from straight fibrils to irregularly shaped, rope-like fibrils. These findings suggest that the Met35 oxidation state and amyloid plaque formation may be intimately linked.Journal of Alzheimer's disease: JAD 05/2013; 37(1). DOI:10.3233/JAD-122389 · 3.61 Impact Factor
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ABSTRACT: Progressive cerebral deposition of the amyloid β-protein (Aβ) in brain regions serving memory and cognition is an invariant and defining feature of Alzheimer disease. A highly similar but less robust process accompanies brain aging in many nondemented humans, lower primates, and some other mammals. The discovery of Aβ as the subunit of the amyloid fibrils in meningocerebral blood vessels and parenchymal plaques has led to innumerable studies of its biochemistry and potential cytotoxic properties. Here we will review the discovery of Aβ, numerous aspects of its complex biochemistry, and current attempts to understand how a range of Aβ assemblies, including soluble oligomers and insoluble fibrils, may precipitate and promote neuronal and glial alterations that underlie the development of dementia. Although the role of Aβ as a key molecular factor in the etiology of Alzheimer disease remains controversial, clinical trials of amyloid-lowering agents, reviewed elsewhere in this book, are poised to resolve the question of its pathogenic primacy.Cold Spring Harbor Perspectives in Medicine 06/2012; 2(6):a006262. DOI:10.1101/cshperspect.a006262 · 7.56 Impact Factor