The characterization of the secretases involved in beta-APP processing in yeast and mammals.
Item
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Title
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The characterization of the secretases involved in beta-APP processing in yeast and mammals.
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Identifier
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AAI3008824
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identifier
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3008824
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Creator
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Espinoza, Daniel Omar.
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Contributor
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Adviser: David L. Miller
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Date
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2001
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience | Biology, Molecular | Biology, Cell
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Abstract
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Accumulation of beta-amyloid peptide (Abeta) is thought to be one of the principal causes of Alzheimer's disease (AD) pathology. Abeta is a metabolic product of the beta-amyloid precursor protein (APP), a type I transmembrane glycoprotein. The enzymes that cleave APP within the Abeta domain are designated alpha-secretases. The enzymes that generate the amino and carboxyl termini of Abeta are respectively designated beta- and gamma-secretase(s). None of these secretases had been identified when this study was started. Much progress has been made in the last 2--3 years. Two beta-secretases were recently identified, and there are now strong candidates for alpha- and gamma-secretases. The identification of these secretases is a major goal of AD research because they regulate accumulation of Abeta. The yeast Saccharomyces cerevisiae was proposed as a model for the identification of human alpha-, beta- and gamma-secretase(s) candidates from a human brain cDNA library. We and others have reported the existence of alpha-secretase activity in yeast that has the same specificity as the human alpha-secretase(s), but no beta- nor gamma-secretase activities could be detected. Two homologous aspartyl proteases, Yps1p and Yps2p seem to be responsible for most of the yeast alpha-secretase. The deletion of two other YPS1-homologous genes did not reduce yeast alpha-secretase activity. A yeast system was developed to screen for human APP secretases from a human cDNA library. The system consists of a yeast acid phosphatase fused at its carboxyl terminus to the last 106 amino acids of human APP, and a yeast strain with almost no APP-secretase activity. This yeast system was tested with reported human secretase candidates. It was found that full length beta-secretases are not expressed at detectable levels in yeast. On the other hand, expression of mature forms of these enzymes can be detected when they are fused to the yeast alpha-mating factor signal sequence. Presenilin 1 was also expressed in yeast and tested as a gamma-secretase candidate, but no gamma-secretase activity could be detected. Other cofactor(s) that are not present in yeast may be needed to activate gamma-secretase.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
