Enzymatic generation of the amino terminus of the beta-amyloid peptide.
The major pathological change in Alzheimer's disease is the deposition of 39-42-amino acid beta-amyloid peptide (BAP) in the brain. Since BAP begins at the aspartate residue (Asp1, or codon 672 of the amyloid precursor protein (APP)770 transcript), the ability of several proteases to cleave the peptide bond methionine-Asp1 (M/D) was evaluated by using peptides and recombinant APP molecules as substrates. Cathepsin G and chymotrypsin cleave the synthetic peptide HSEVKMDAEF at M/D under acidic conditions, whereas cleavage at lysine-methionine (K/M) predominates when the pH is alkaline. Trypsin and cathepsins B, D, and L are unable to cleave the synthetic peptide at M/D. Peptide SEVNLDAEF, representing the mutation found in early onset Alzheimer's disease families from Sweden, is cleaved by cathepsin G and chymotrypsin at leucine-aspartate (L/D). Incubation of cathepsin G with soluble protease nexin-2 obtained from recombinant APP (APP-REP) derivatives resulted in proteolytic cleavage at or near the amino terminus of BAP. Cathepsin G-mediated cleavage was also observed in the domain representing the amino terminus of BAP when mature plasma membrane-associated APP-REP molecules were used as substrates. Our results strongly suggest the involvement of a chymotrypsin-like serine protease in the generation of the amino terminus of BAP beginning at Asp1.
Sahasrabudhe
S R
SR
Central Nervous System Biological Research Department, Lederle Laboratories, American Cyanamid Company, Pearl River, New York 10965.
Brown
A M
AM
Hulmes
J D
JD
Jacobsen
J S
JS
Vitek
M P
MP
Blume
A J
AJ
Sonnenberg
J L
JL
D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism; D002918:Chymotrypsin / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000378:metabolism; D011233:Precipitin Tests; D012697:Serine Endopeptidases / Q000378:metabolism*; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism
D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; D002403:Cathepsins; D012697:Serine Endopeptidases; D002918:Chymotrypsin; C534094:CTSG protein, human; D056649:Cathepsin G; D014357:Trypsin