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Protein Sci. 2009 Feb;18(2):277-86. doi: 10.1002/pro.33.

Discovery of amyloid-beta aggregation inhibitors using an engineered assay for intracellular protein folding and solubility.

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Cornell University, Ithaca, New York 14853, USA.


Genetic and biochemical studies suggest that Alzheimer's disease (AD) is caused by a series of events initiated by the production and subsequent aggregation of the Alzheimer's amyloid beta peptide (Abeta), the so-called amyloid cascade hypothesis. Thus, a logical approach to treating AD is the development of small molecule inhibitors that either block the proteases that generate Abeta from its precursor (beta- and gamma-secretases) or interrupt and/or reverse Abeta aggregation. To identify potent inhibitors of Abeta aggregation, we have developed a high-throughput screen based on an earlier selection that effectively paired the folding quality control feature of the Escherichia coli Tat protein export system with aggregation of the 42-residue AD pathogenesis effecter Abeta42. Specifically, a tripartite fusion between the Tat-dependent export signal ssTorA, the Abeta42 peptide and the beta-lactamase (Bla) reporter enzyme was found to be export incompetent due to aggregation of the Abeta42 moiety. Here, we reasoned that small, cell-permeable molecules that inhibited Abeta42 aggregation would render the ssTorA-Abeta42-Bla chimera competent for Tat export to the periplasm where Bla is active against beta-lactam antibiotics such as ampicillin. Using a fluorescence-based version of our assay, we screened a library of triazine derivatives and isolated four nontoxic, cell-permeable compounds that promoted efficient Tat-dependent export of ssTorA-Abeta42-Bla. Each of these was subsequently shown to be a bona fide inhibitor of Abeta42 aggregation using a standard thioflavin T fibrillization assay, thereby highlighting the utility of our bacterial assay as a useful screen for antiaggregation factors under physiological conditions.

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