title: Degradation of tau by lysosomal enzyme cathepsin D: implication for Alzheimer neurofibrillary degeneration.
abstract: The degradation of different isoforms of human recombinant tau (R-tau; T39, T40, and T44) and fetal tau (F-tau) by cathepsin D (CD) was investigated. Gel electrophoresis and Coomassie Blue staining of different R-tau species digested at pH 3.5 showed very little differences in CD susceptibility. Immunoblotting analyses revealed that amino and carboxy termini of tau were cleaved before other regions. F-tau was most vulnerable to proteolysis at both termini. Digestion of R-tau with 0.01 unit of CD/ml at pH 3.5 resulted in cleavage between Phe8-Glu9, Met419-Val420, Thr427-Leu428-Ala429, and Leu436-Ala437 as determined by amino acid sequencing and mass spectroscopy (numbering of amino acids was based on T40). With higher concentrations of CD (1 unit/ml), additional sites of digestion were detected between amino acids 34-161, 200-257, and 267-358. The cleavage sites at amino acids 34-161 and 267-358 were observed at pH 3.5, whereas that at amino acids 200-257 was detected at pH 7.0. Our results suggest that CD cleavage of tau could generate tau fragments with intact microtubule binding domains, which could have a role in the pathogenesis of paired helical filaments (PHFs) in Alzheimer's disease. Such proteolysis might also contribute to the changes of PHF phenotype observed in intracellular and extracellular tangles.
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York 10461, U.S.A.
authors.forename: A
authors.initials: A
authors.lastname: Kenessey
authors.forename: P
authors.initials: P
authors.lastname: Nacharaju
authors.forename: L W
authors.initials: LW
authors.lastname: Ko
authors.forename: S H
authors.initials: SH
authors.lastname: Yen
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism / Q000473:pathology*; D000595:Amino Acid Sequence; D000818:Animals; D002402:Cathepsin D / Q000378:metabolism*; D002417:Cattle; D005333:Fetus; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008247:Lysosomes / Q000201:enzymology*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009410:Nerve Degeneration / Q000378:metabolism* / Q000473:pathology; D016874:Neurofibrillary Tangles / Q000378:metabolism / Q000473:pathology*; D009454:Neurofibrils / Q000378:metabolism / Q000473:pathology*; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013154:Spleen / Q000201:enzymology; D016875:tau Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D011994:Recombinant Proteins; D016875:tau Proteins; D002402:Cathepsin D