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M9480544.TXT
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1994-08-20
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Document 0544
DOCN M9480544
TI Cleavage at the amino and carboxyl termini of Alzheimer's amyloid-beta
by cathepsin D.
DT 9410
AU Ladror US; Snyder SW; Wang GT; Holzman TF; Krafft GA; Abbott
Laboratories, Abbott Park, Illinois 60064.
SO J Biol Chem. 1994 Jul 15;269(28):18422-8. Unique Identifier : AIDSLINE
MED/94308073
AB Amyloid beta (A beta) is a 39-43-residue protein that originates from
proteolysis of the beta-protein precursor (beta PP) and accumulates in
senile plaques in brains of Alzheimer's disease (AD) patients. Mutant
beta PP, which incorporates an AD-causing double mutation at positions
687-688, has been shown to enhance A beta production in transfected
cells. In this work we investigate the susceptibility of the mutant beta
PP sequence to proteolytic cleavage by proteinases from human brain.
Internally quenched fluorogenic substrates were used that encompass the
NH2-terminal sequence of A beta from wild-type beta PP, the double
mutant, and the two single substitutions. Proteinase activity in brain
extract cleaved the mutant substrate 100-fold faster than the wild-type
substrate and the partial mutants 25-fold faster. The major cleavage
site in all substrates was at the amyloidogenic Asp1 site. The brain
activity appeared to be cathepsin D (CD), as indicated by similarities
to purified CD in 1) the rate and site of substrates cleavage, 2) the pH
optima, and 3) the sensitivity to pepstatin A. The increased activity
against the mutant substrate was not shared by cathepsins B and C,
pepsin, HIV proteinase, and Candida albicans Asp-proteinase.
Furthermore, CD cleaved a substrate that incorporates the COOH terminus
of A beta at positions equivalent to Thr43 and Ala42, at ratios of 68%
and 32%, respectively. CD degraded A beta 1-40 into six fragments but A
beta 1-42 was completely resistant to digestion, probably because of its
aggregation characteristics. These results indicate that CD is capable
of producing the cleavages resulting in A beta production and that it
may prove to be a suitable therapeutic target.
DE Amino Acid Sequence Amyloid beta-Protein/*METABOLISM Brain/*ENZYMOLOGY
Cathepsin D/*METABOLISM Comparative Study Frontal Lobe/*METABOLISM
Human Hydrogen-Ion Concentration Kinetics Molecular Sequence Data
Oligopeptides/*METABOLISM Pepstatins/PHARMACOLOGY Peptide
Peptidohydrolases/*METABOLISM Point Mutation Substrate Specificity
Support, U.S. Gov't, P.H.S. Time Factors JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).