Identification of a chymotrypsin-like mast cell protease in rat brain capable of generating the N-terminus of the Alzheimer amyloid beta-protein.
Cleavage after Met596 of the beta-amyloid precursor protein to generate the N-terminus of beta-protein indicates the activity of a protease having chymotrypsin-like specificity. A chymotrypsin-like protease is further implicated in Alzheimer's disease by the increased synthesis of the protease inhibitor alpha 1-antichymotrypsin in pathologically affected brain regions and by the presence in the amyloid deposits of inactivated forms of alpha 1-antichymotrypsin (indicating irreversible binding to a target chymotrypsin-like protease). In the present report, we have purified from rat brain a chymotrypsin-like protease that (a) binds with high affinity to human alpha 1-antichymotrypsin, (b) proteolytically generates a beta-protein-containing C-terminal fragment from full-length recombinant human beta-amyloid precursor protein, and (c) selectively cleaves methoxysucinyl-Glu-Val-Lys-Met- p-nitroanilide (a substrate modeling the protease recognition domain for the beta-protein N-terminal cleavage site). Amino acid sequences of tryptic fragments of the purified rat brain chymotrypsin-like protease indicate an identity with rat mast cell protease I. Moreover, the ontogeny and compartmentalization of rat brain chymotrypsin-like protease are consistent with those of connective tissue-type mast cells in the meningeal and intracortical perivasculature. Because these areas in human brain form extensive beta-amyloid deposits in Alzheimer's disease, Down's syndrome, and hereditary cerebral hemorrhage with amyloidosis of Dutch origin, the present findings suggest that a brain mast cell chymotrypsin-like protease may participate in generating perivascular beta-protein, which ultimately aggregates into beta-amyloid deposits.
Nelson
R B
RB
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
Siman
R
R
Iqbal
M A
MA
Potter
H
H
D000544:Alzheimer Disease / Q000378:metabolism; D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D053818:Chymases; D007700:Kinetics; D008407:Mast Cells / Q000201:enzymology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D051381:Rats; D017421:Sequence Analysis; D012697:Serine Endopeptidases / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D014018:Tissue Distribution
D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; D012697:Serine Endopeptidases; D053818:Chymases